JOURNAL PAPERS

Abstract: Biofuels are known to have several advantages over fossil fuels including, but not limited to, high abundance of resources, negligible SOx emissions, lower NOx emissions, and more environment-friendly processes. In the Philippines, the biofuels industry is anchored onto the Biofuels Act of 2006 which mandates the use of biofuels made from indigenous sources such as coconut. Despite this, biodiesel is still less preferred by consumers over conventional fuel due to its high cost. This can be attributed to high production costs of biodiesel, wherein 18-28% is credited to transportation of products.  This work proposes a linear programming model to reduce the overall cost of biodiesel by minimizing the transportation cost in the Philippine biodiesel supply chain, using the Mindanao cluster as case study. Multiple scenarios were done to gauge the impact of varying the supply allocation and biodiesel blend on the supply chain. The optimal supply allocation, transportation cost, and carbon footprint of each scenario were determined. A new facility locator feature was also added as an extension of the program. Results also showed high reproducibility using easily accessible programming tools such as Microsoft Excel and Python.

Abstract:

Rational design of new and cost-effective advanced batteries for the intended scale of application is concurrent with cathode materials development. Foundational knowledge of cathode materials’ processing–structure–properties–performance relationship is integral. In this review, we provide an overview of borate-based compounds as possible mixed polyanion cathode materials in organic electrolyte metal-ion batteries. A recapitulation of lithium-ion battery (LIB) cathode materials development provides that rationale. The combined method of data mining and high-throughput ab initio computing was briefly discussed to derive how carbonate-based compounds in sidorenkite structure were suggested. Borate-based compounds, albeit just close to stability (viz., <30 meV at−1), offer tunability and versatility and hence, potential effectivity as polyanion cathodes due to (1) diverse structures which can host alkali metal intercalation; (2) the low weight of borate relative to mature polyanion families which can translate to higher theoretical capacity; and a (3) rich chemistry which can alter the inductive effect on earth-abundant transition metals (e.g., Ni and Fe), potentially improving the open-circuit voltage (OCV) of the cell. This review paper provides a reference on the structures, properties, and synthesis routes of known borate-based compounds [viz., borophosphate (BPO), borosilicate (BSiO), and borosulfate (BSO)], as these borate-based compounds are untapped despite their potential for mixed polyanion cathode materials for advanced batteries.

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Abstract:

The global transition towards net-zero greenhouse gas emissions establishes a need for cleaner energy technologies. Hydrogen is a promising energy carrier whose global demand is steadily increasing and is conventionally produced through steam-methane reforming with carbon capture, or blue H2. Hydrogen production supplied by renewable energy (green H2) is an emerging process, but developing countries are not yet ready for a full transition. Augmenting blue H2 with green H2 production will allow a smoother transition until green H2 costs significantly decrease by 2050. In this work, a novel, low-cost teal hydrogen (teal H2) plant, a mixture of blue and green H2 technologies, located in the Philippines which combines steam-methane reforming, rice husk gasification, and carbon capture by monoethanolamine absorption, is proposed. Setting a production rate of 9,000 kg H2/h, the techno-economic potential of five cases with varying natural gas to rice husk contribution ratios were evaluated using AspenPlus. The levelized cost of the 25:75 teal H2 case at 1.06 USD/kg is cheaper than blue H2 and green H2 by 4.37 and 2.34 USD/kg, respectively. Moreover, the CO2-equivalent emissions of the 25:75 teal H2 case at 0.002 t CO2 -eq/1,000 Nm3 H2 is 57.10 % and 39.25 % lower than those from blue H2 and green H2. As green H2 becomes more economical, rice husk feed to the gasification process can be gradually increased to favor biomass- over petroleum-derived H2. This case study is a successful proof of concept that teal H2 may help transition the energy sector to carbon neutrality.

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Abstract:

Different energy storage technologies have particular applications with advantageous techno-economic characteristics. For this reason, the present and future Levelised Costs Of Storage (LCOS) of commercially mature energy storage technologies have been analysed in the current literature. Emerging energy storage technologies, such as long-duration flywheels, are also vying to capture the energy storage market, but uncertainties linger as to which applications they can capture due to limited and reliable publicly available data. In this work, we determined the future LCOS of a typical 1 MW installation of stationary electrochemical energy storage (lead-acid, sodium-sulphur, and lithium-ion battery) and mechanical energy storage technologies (short-duration flywheel and long-duration flywheel) under different applications from 2020 to 2050 using updated relevant techno-economic parameters. Based on the present costs of energy storage, lithium-ion batteries yield the lowest LCOE across different energy storage applications, corroborating with previous outlooks from different scholarly works. The cost advantage of lithium-ion batteries compared to other storage technologies continues to rise over the years due to their rapid cost decline. In the absence of lithium-ion batteries, long-duration flywheels initially provide the lowest cost for a wide range of applications, but they face stiff competition with sodium-sulphur batteries. By 2040, sodium-sulphur batteries are projected to have a lower LCOS than long-duration flywheels. Promoters and manufacturers of emerging energy storage technologies must find ways to rapidly decrease storage costs to secure their niche in the energy storage market.

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Abstract: 

Ethylene glycol dimethacrylate (EGDMA) – dithiadiamide (DTDA) copolymer was synthesized by condensation reaction between monomeric mercaptoacetamide and ?-dibromoalkanes. This previously designed DTDA was complexed with Pt2+ before direct copolymerization with EGDMA. Pt2+-template was eluted with dilute HCl. The EGDMA-DTDA copolymer was evaluated for Pt2+ adsorption in terms of adsorption isotherm and selectivity. The copolymer exhibited monolayer Langmuir-type adsorption isotherm with qm = 177 mg g-1 at optimum pH = 1. It is selective to Pt2+ in a simulated solution containing the predominant cations present in an acid-leached spent 3-way, gasoline automobile catalytic converter sample (i.e., Al3+, Ba2+, Ce3+, Fe2+, Mg2+, and Zn2+).

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Abstract:

A new class of technology known as transient electronics has the potential to reduce electronic waste with its unique ability to dissolve under a specific condition. Biodegradable batteries are essential to realizing fully integrated and self-sufficient systems. Pure magnesium-based materials are among the widely explored transient electrodes due to their superior mechanical properties. However, such materials have rapid degradation rates. AZ31, an alloy of Mg containing 3 % aluminum (Al) and 1 % zinc (Zn) by weight, has more stable corrosion product layers, making them advantageous as anode materials. In this work, the electrochemical performance of the two full cell combinations of Mg and AZ31 anodes each paired with copper oxide (CuO) cathode were compared in a seawater electrolyte. To produce the cathodes, pristine copper foils were galvanostatically anodized at a current density of 2.0 mA/cm2 for 90 min. Results showed that AZ31-based cell has a higher specific energy of 1.63 J/cm2 compared to pure Mg-based cell which has 1.08 J/cm2. The observed nominal operating voltages for an AZ31-based cell were 1.1 V for the first 0.6 h and remained at 0.8 V for the next 5.6 h when discharged at a current density of 0.25 mA/cm2. The AZ31-based cell also yields a better specific capacity of 2.17 mAh/cm2 and a discharge time of 8.68 h, which is twice the capacity and the discharge life of a pure Mg-based cell. The reported increase in performance is attributed to the presence of alloying components in the anode which limits the parasitic corrosion inherent in a pure Mg anode.

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Abstract:

In this work, we propose an immersion corrosion measurement method with E10 bioethanol-gasoline blend on austenitic steel (SS304) and aluminum (Al6061). Immersion tests were designed to simulate a weekly refuel cycle and were performed over 4, 8, and 12-week durations. Polarization resistance, surface morphology, and corrosion products were then observed after the immersion tests. Corrosion rates were estimated from polarization resistance measurements via electrochemical impedance spectroscopy. Afterwards, the surface morphology of exposed samples was studied using scanning electron microscopy. Lastly, the corrosion products were characterized using scanning electron microscopy with energy dispersive X-ray analysis. Surface staining was observed in both metal substrates. It was observed that the corrosion rate of SS304 remained relatively constant throughout the immersion time. In contrast, an increment in the corrosion rate of Al6061 was observed after four weeks of immersion due to the peeling of the protective oxide layer.

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Abstract:

The global transition towards net-zero greenhouse gas emissions establishes a need for cleaner energy technologies. Hydrogen is a promising energy carrier whose global demand is steadily increasing and is conventionally produced through steam-methane reforming with carbon capture, or blue H2. Hydrogen production supplied by renewable energy (green H2) is an emerging process, but developing countries are not yet ready for a full transition. Augmenting blue H2 with green H2 production will allow a smoother transition until green H2 costs significantly decrease by 2050. In this work, a novel, low-cost teal hydrogen (teal H2) plant, a mixture of blue and green H2 technologies, located in the Philippines which combines steam-methane reforming, rice husk gasification, and carbon capture by monoethanolamine absorption, is proposed. Setting a production rate of 9,000 kg H2/h, the techno-economic potential of five cases with varying natural gas to rice husk contribution ratios were evaluated using AspenPlus. The levelized cost of the 25:75 teal H2 case at 1.06 USD/kg is cheaper than blue H2 and green H2 by 4.37 and 2.34 USD/kg, respectively. Moreover, the CO2-equivalent emissions of the 25:75 teal H2 case at 0.002 t CO2 -eq/1,000 Nm3 H2 is 57.10 % and 39.25 % lower than those from blue H2 and green H2. As green H2 becomes more economical, rice husk feed to the gasification process can be gradually increased to favor biomass- over petroleum-derived H2. This case study is a successful proof of concept that teal H2 may help transition the energy sector to carbon neutrality.

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Abstract:

Accurately estimating the capacity degradation of lithium-ion (Li-ion) batteries is vital in ensuring their safety and reliability in electric vehicles and portable electronics. Future capacity estimation using machine learning (ML) models allow battery lifetime predictions with minimal cycling data in the train set, well before capacity degradation occurs within the cell. The use of ML methods removes the need for prior knowledge of cell chemistry and the physical and chemical behaviors of batteries. In this paper, the data-driven ML models Gaussian process regression (GPR) and recurrent neural network – long short-term memory (RNN-LSTM) estimated the charge capacity of Li-ion batteries from the Oxford Battery Dataset, using only the battery's cycle index and capacity as input. With only 15 % of the battery’s lifetime as training data, the GPR model achieved a mean average percent error (MAPE) of 8.335 % and an R2 of 0.9755, while the LSTM model achieved a MAPE of 9.984 % and an R2 of 0.9898. These results indicate the goodness of fit and are comparable to results from similar models in the literature (MAPE = 9.1 to 15 %). The methodology may be applied to different features to help establish the relationship between health indicators and capacity fade and can be used in applications that require early capacity prediction such as in space technologies where lifetime and capacity are crucial in ensuring success and safety. This successful estimation highlights the promise and potential of accurately predicting Li-ion battery capacity degradation using a single-feature approach.

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Abstract:

The renewable energy transition requires energy storage technologies for grid-balancing and transportation. Lithium-ion batteries have been widely adopted for these applications, but supply risks due to geopolitical tensions have motivated the search for alternative chemistries less dependent on critical raw materials. Sodium-ion batteries have garnered notable attention as promising post-lithium chemistry due to the relative abundance of sodium and its similar manufacturing process to lithium-ion batteries. This work estimated the cost of producing sodium-ion battery packs from cells optimized via multiphysics modeling for energy or power-based applications. This study replicated a multiphysics model of a pouch format sodium-ion battery from literature in COMSOL Multiphysics®. This model determined the optimal active material used in batteries under 0.1C to 10C discharge rates to maximize the energy density. The cost of battery packs produced from the optimized cells was then determined using the Battery Performance and Cost (BatPaC) model of Argonne National Laboratory, which considers material and manufacturing costs. The optimization results reveal that energy cells have thicker electrodes and lower porosities (217 µm thick 0.11 porosity anode, 237 µm thick 0.10 porosity cathode for 0.1C), which maximize the amount of active material per unit mass. Power cells have thinner electrodes and larger porosities to minimize electrical resistance (58 µm thick 0.32 porosity anode, 63 µm thick 0.31 porosity cathode for 10C), reducing energy losses at high currents. Moreover, we compared the calculated production cost for energy and power applications for sodium-ion batteries, highlighting essential parameters affecting the price. The model observed a 26.42% increase in total material cost per kWh when transitioning from energy to power cells. The model may also be refined by considering sodium-ion batteries with different cathode and anode chemistries in different formats and their applications in different use cases.

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Abstract:

With the rising energy demand, safe and efficient energy storage technologies have been increasing in importance. Lithium Polymer (LiPo) batteries use a gel polymer to act as both separator and electrolyte, which is thermally and electrochemically more stable and safer than conventional liquid electrolytes. Besides exploring new materials, engineering a reliable multiphysics model is vital to exploiting and optimizing existing LiPo batteries' potential. This study developed a multiphysics model for a Lithium Cobalt Oxide (LCO)-graphite- Poly(vinylidene fluoride - hexafluoropropylene) (PVdF-HFP) pouch-type mobile phone LiPo. A pseudo-2-dimensional electrochemical model was coupled with a 3D thermal model using COMSOL Multiphysics® to determine the working voltage and temperature during discharge and was compared with experimental data from a commercial LiPo battery and evaluated using Root Mean Square Error (RMSE). The simulated discharge curve agrees remarkably well with the experimental results. The simulated temperature profile has shown appreciable discrepancies primarily due to the generated entropic change coefficient values that significantly affect the battery's heat generation. Overall, the models can be employed as a design tool to evaluate the component design and estimate the system performance of LiPo batteries for commercial applications. Furthermore, researchers can expand the study to investigate more advanced electrochemical phenomena and performances of state-of-the-art lithium and post-lithium chemistries.

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Abstract:

Many people around the world rely on groundwater for drinking and sanitation, however, they are exposed to various health risks from the naturally occurring groundwater arsenic (As). Air-cathode Assisted Iron Electrocoagulation (ACAIE) using Carbon Black Pearls 2000® cathode was previously shown catalyse the removal of groundwater As by producing hydrogen peroxide (H2O2). This work explored Vulcan® XC-72, and Printex® L6 Carbon as alternative cathodes for iron electrocoagulation which are more selective towards the 2-electron oxygen reduction reaction into H2O2 compared to Carbon Black Pearls®. The cathodes were tested in an ACAIE set-up to treat synthetic groundwater spiked with 1,500 µg/L of As at different charge dosage rates (CDR) from 1.56 C/L-min to 100 C/L-min with a total charge dosage of 600 C/L for all set-ups. Although the electrocoagulation energies among the cathodes were similar, the use of Printex® cathode for ACAIE remediated the groundwater for all CDR with final As levels below 10 µg/L. This is in contrast with the less selective Carbon Black Pearls® at low CDR, and the less active Vulcan® Carbon at high CDR where the treated groundwater may still have As levels above 10 µg/L. Future research would explore modifications in the carbon materials and reactor configuration to further optimize ACAIE in removing groundwater As.

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Abstract:

The global mission to reduce fossil fuel consumption has led to the escalating demand for electrochemical energy storage (EES) devices such as fuel cells and batteries. Computational techniques like Density Functional Theory (DFT) have recently been coupled with Machine Learning (ML) for high-throughput material screening and discovery. Transition metal surfaces are popular electrocatalyst candidates, but predictive ML regression models have only been applied to select metals such as Pt and Cu. Additionally, characterizing the contributions of each feature is challenging, especially on black-box models. In this work, regression models were trained to predict the adsorption energies of carbon, hydrogen, and oxygen on 27 fcc (111) monometallic surfaces and applied model-agnostic interpretation methods to evaluate feature importance. Over 200 adsorption energies on transition metal surfaces were collected from Catalysis-hub.org, a surface reaction database. A dataset was constructed for each adsorbate, and was composed of ten surface atomic, surface electronic, and adsorbate properties collected from online databases and DFT calculations on adsorbate-free surfaces. Then, the fine-tuned random forest regression, Gaussian process regression, and artificial neural network models predicted atomic adsorption energies while permutation feature importance calculated feature contributions. All ML model accuracies were found to be competitive with those from literature, with Gaussian process regression reporting the lowest errors of the three models. Coordination number was also found to have the largest contributions for all models. ML-DFT methodologies such as this can be expanded to accommodate alloys and more adsorbates for a wider screening of potential EES materials.

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Abstract:

Acid-alkaline electrolyzers utilize an acidic catholyte and alkaline anolyte, which lower the thermodynamic voltage requirement for water splitting. Experiments have demonstrated the feasibility of acid-alkaline electrolyzers with proton exchange membranes, but a mathematical model has yet to be developed to understand their operation. This work developed a multiphysics model of a batch acid-alkaline electrolyzer with a H2SO4 catholyte, a NaOH anolyte, and a proton exchange membrane. The model was formulated in COMSOL Multiphysics® and validated using experimental current vs. voltage data in literature. The electrolyzer’s reactions and ion transport were analyzed based on the electrolyte potential, concentration profiles, and ion fluxes calculated by the model. The charge imbalance due to the consumption of H+ and OH- in the catholyte and anolyte, respectively, is addressed by Na+ transport from the anolyte to the catholyte. This contradicts the prevailing hypothesis that electroneutrality in a proton exchange membrane acid-alkaline electrolyzers is preserved by the Second Wien Effect, or water splitting in high electric fields. H+ is transported from the catholyte to the anolyte, which results in undesired acid-base neutralization. This is minimized by increasing the applied voltage, which shows a tradeoff between power and reactant consumption. Na+-selective membranes also hinder the neutralization reaction, but their realization is challenging due to the smaller Stokes radius of H+. The proposed model can be used to optimize the parameters of a batch electrolyzer and aid in the design of a continuous electrolyzer stack.

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Abstract:

Primary alkaline batteries have been widely used in portable electronics due to their low cost and safety. The consumption and disposal of these batteries has prompted notable research on their recycling. Another approach to reducing alkaline battery disposal is to extend their lifetime by increasing their energy density. In this work, the energy density of an AA primary alkaline battery was maximized by determining the optimum amount of electrode materials through multiphysics modeling. An electrochemical model of the alkaline battery is developed in COMSOL Multiphysics® and validated with discharge curves (i.e., voltage vs. time) obtained under constant resistance loads. The electrode thicknesses are then optimized to maximize the energy density of the battery while maintaining its exterior dimensions. The sensitivity of the energy density with respect to the electrode porosities and interfacial areas is then analyzed. The electrochemical model was able to replicate the discharge curves obtained under a 250 mA constant current discharge. The energy density is maximized by decreasing the thickness of the zinc anode. However, this results in anode dissolution near the current collectors and could compromise the electrical continuity in the battery. Increasing the anode thickness prevents dissolution at the current collectors but increases unused mass in the battery. The results of this study can be used to develop longer-lasting alkaline batteries. Furthermore, the model can be improved by considering thermal effects or modified to aid the development of rechargeable alkaline batteries.

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Abstract:

Sodium-sulfur (NaS) batteries are a promising energy storage technology that features high energy density, high cycle life, and no self-discharge. One of the cell design considerations that can affect the performance and construction of NaS batteries is cell geometry. While the planar geometry has advantages in power output, cell packing, ease of assembly, and thermal management, it has thermo-mechanical issues in sealing, which makes it less commercialized than the tubular geometry. In this work, the first multiphysics model of a NaS cell with a planar geometry was developed by extending an existing multiphysics model for a NaS cell with a tubular geometry. A previously developed multiphysics model for the tubular NaS cell was first adapted into COMSOL Multiphysics®. The model’s results were then validated against experimental discharge profiles and surface temperatures. After this, a planar NaS cell was simulated using the dimensions of an experimental planar cell, with the mass, heat, and charge transfer equations and parameters previously used in the tubular multiphysics model. The results from the planar model were then validated through comparison to experimental discharge profiles for a planar cell. The developed model can be used in future research and development of NaS batteries by comparing performance parameters of the planar geometry such as discharge profiles, energy densities, and temperatures with a multiphysics model of the tubular NaS battery.

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Abstract:

This data article contains the location, energy consumption, renewable energy potential, techno-economics, and profitability of hybrid renewable energy systems (HRES) in 634 Philippine off-grid islands. The HRES under consideration consists of solar photovoltaics, wind turbines, lithium-ion batteries, and diesel generators. The islands were identified from Google Maps™, Bing Maps™, and the study of Meschede and Ocon et al. (2019) [1]. The peak loads of these islands were acquired from National Power Corporation – Small Power Utilities Group (NPC-SPUG), if available, or estimated from the island population otherwise. Hourly-resolution load profiles were synthesized using the normalized profiles reported by Bertheau and Blechinger (2018) [2]. Existing diesel generators in the islands were compiled from reports by NPC-SPUG, while monthly average global horizontal irradiance and wind speeds were taken from the Phil-LIDAR 2 database. Islands that are electrically interconnected were lumped into one microgrid, so the 634 islands were grouped into 616 microgrids. The HRES were optimized using Island System LCOEmin Algorithm (ISLA), our in-house energy systems modeling tool, which sized the energy components to minimize the net present cost. The component sizes and corresponding techno-economic metrics of the optimized HRES in each microgrid are included in the dataset. In addition, the net present value, internal rate of return, payback period, and subsidy requirements of the microgrid are reported at five different electricity rates. This data is valuable for researchers, policymakers, and stakeholders who are working to provide sustainable energy access to off-grid communities. A comprehensive analysis of the data can be found in our article “Techno-economic and Financial Analyses of Hybrid Renewable Energy System Microgrids in 634 Philippine Off-grid Islands: Policy Implications on Public Subsidies and Private Investments” [3].

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Abstract:

The high energy requirement of hydrogen generation via water splitting has motivated the development of acid-alkaline electrolyzers, which have a lower thermodynamic voltage requirement than conventional electrolyzers. Proton exchange membrane acid-alkaline electrolyzers have been reported in literature, but its reactions and ion transport mechanisms are still unknown. In this work, we developed a multiphysics model of a proton exchange membrane acid-alkaline electrolyzer to elucidate the mechanism of operation. The model showed that Na+ crossover from the anolyte to the catholyte is the primary mechanism for retaining electroneutrality, in contrast with the prevailing hypothesis that H+ is the primary charge carrier. Moreover, we found that H+ is transported from the catholyte to the anolyte, which is counterproductive towards maintaining electroneutrality and results in the undesired acid-base neutralization reaction. Increasing the applied current reduces H+ crossover, thereby demonstrating a tradeoff between power consumption and side reaction minimization. As the cell is operated, the catholyte composition changes from H2SO4 to a mixture of NaHSO4 and Na2SO4, which in turn reduces the overall efficiency. Therefore, in addition to water, proton exchange membrane acid-alkaline electrolyzers will require constant feeding of fresh electrolyte to maintain its performance, and this poses a barrier towards its practical use.

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Abstract:

Batteries are pivotal towards the decarbonization of energy systems as they address the intermittent nature of renewable energy technologies. The techno-economic feasibility of deploying batteries in microgrids is often analyzed using energy systems modeling tools. These often utilize the idealized battery model, which is simpler but neglects electrochemical phenomena. Reduced-order models, which are derived from continuum-scale physics-based models, have improved accuracy but are yet to be applied in the cost optimization of microgrids. In this work, we proposed a novel methodology for generating reduced-order models of lithium-ion lithium iron phosphate, nickel cobalt aluminum oxide, and nickel manganese cobalt chemistries for use in the techno-economic optimization of microgrids. We simulated previously reported multiphysics models of Li-ion batteries in COMSOL Multiphysics® and reduced them into equivalent circuit models. These were implemented in Island Systems LCOEmin Algorithm (ISLA), our in-house energy systems modeling and optimization tool. We then simulated and optimized renewable energy systems in ISLA to determine the discrepancy between the reduced-order equivalent circuit models versus the idealized battery model. The results revealed that the idealized battery model can miscalculate the SOC by >5 % SOC due to the assumption of constant voltages, while the optimum sizes differed by >5 % when there are sharp peaks in demand or if non-renewable sources are competitive. The idealized battery model is therefore not a valid approximation under these scenarios. This work demonstrated a novel multi-scale framework from the continuum-scale multiphysics modeling of batteries to macroscale energy systems optimization.

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Abstract:

Increased utilization of renewable energy (RE) resources is critical in achieving key climate goals by 2050. The intermittent nature of RE, especially solar and wind, however, poses reliability concerns to the utility grid. One way to address this problem is to harmonize the RE resources using spatio-temporal complementarity analysis. Two RE resources are said to be complementary if the lack of one is balanced by the abundance of the other, and vice versa. In this work, solar–wind complementarity was analyzed across the provinces of Kalinga and Apayao, Philippines, which are potential locations for harvesting RE as suggested by the Philippine Department of Energy. Global horizontal irradiance (GHI) and wind speed data sets were obtained from the NASA POWER database and then studied using canonical correlation analysis (CCA), a multivariate statistical technique that finds maximum correlations between time series data. We modified the standard CCA to identify pairs of locations within the region of study with the highest solar–wind complementarity. Results show that the two RE resources exhibit balancing in the resulting locations. By identifying these locations, solar and wind resources in the Philippine islands can be integrated optimally and sustainably, leading to a more stable power and increased utility grid reliability.

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Abstract:

In line with one of the objectives of Sustainable Development Goal 7 to close energy poverty, the techno-economic feasibility of deploying hybrid renewable energy systems (HRES) in Philippine off-grid islands has been extensively studied to address reliance on diesel generators in these areas. Several works have analyzed HRES deployment at a nationwide level in terms of levelized costs, but the financial sustainability in terms of profits and subsidies of such schemes is largely unexplored. In this work, we analyzed the potential profits and subsidy requirements of HRES in 634 Philippine off-grid islands. First, we developed a database of inhabited off-grid islands containing their load profiles and solar and wind resources. A techno-economic analysis was then performed by sizing HRES with solar photovoltaics, wind turbines, lithium-ion batteries, and diesel generators in each island to minimize net present costs. A profitability analysis was then carried out by calculating profitability metrics, such as the net present value, internal rate of return, and payback period at various tariff rates. The techno-economic analysis revealed that larger islands had a higher proportion of RE technologies, which decreased long-term costs but increased capital costs. Meanwhile, the profitability analysis showed that HRES projects in larger islands become profitable at lower electricity rates but require larger subsidies to maintain when they are unprofitable. In this regard, we argue that government subsidies should be targeted towards smaller islands, while the private sector should be enticed to invest in larger islands. This work demonstrates that quantifying subsidies and profits, and not just the costs, of HRES can yield better insights on the economics of HRES deployment. Moreover, this work highlights the importance of government subsidies and private sector participation for achieving 100% energy access in the Philippines.

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Abstract:

Different energy storage technologies can be potentially integrated into microgrids to support variable renewable energy generators. Long-duration flywheel energy storage is considered a new contender in the energy storage market. This energy storage technology has been previously evaluated in a techno-economic study, but it did not consider uncertainties in the model input data. In this work, stochastic techno-economic comparison is performed using microgrid modeling and Monte-Carlo methods to compare long-duration flywheels, lithium-ion batteries, and lead-acid batteries for isolated microgrid and industrial facility. Results generally show a relatively high probability for long-duration flywheels to yield a lower leveized cost of storage (LCOS) and levelized cost of electricity (LCOE) compared to lithium-ion batteries in 2020. Higher probability can be attained when the overnight component cost of long-duration flywheels is reduced or when overnight diesel prices are high. However, the chances of long-duration flywheels yielding lower LCOS and LCOE rapidly decreases as time progresses. Long-duration flywheel manufacturers and promoters must find ways to accelerate price reduction by 2.5× from baseline to secure a better chance of yielding a lower LCOS in 2050.

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Abstract:

Renewable energy systems are a critical game changer of the 21st century, where various fundamental and applied researches are realised for advancing the practicality of energy provision at a multitude of scales. This study aimed to unravel the roles of H+, Na+ and K+ cations over the self-photorechargeability of a novel Pt/MoO3 photoanode-driven photoelectrochemical (PEC) system with dual-functionalities of solar photon-to-electron conversion and storage of electrons. FE-SEM analysis showed that the Pt/MoO3 photoanode consists of a 3D plate-like surface structure with favourable void spaces and internal channels for promoting the photo-intercalation and de-intercalation reactions. HR-TEM analysis validated the formation of interfacial heterojunction between Pt co-catalyst and MoO3 in Pt/MoO3 photoanode for improving the overall work function as well as synergising the self-photorechargeability properties. Further current and charge density profiling for the Pt/MoO3-driven self photorechargeable system over three consecutive charging-discharging cycles demonstrated a slow charge decay kinetics in H+ electrolyte resulted in a relatively high charge density of 5.53 mC/cm2. EIS Nyquist analysis depicted a smaller arc radius in the Nyquist plot of the Pt/MoO3-driven self photorechargeable system which indicates a lower charge transfer impedance and thus, facilitating a better separation efficiency of electron-hole pairs than bare MoO3. From the systematic study on H+, Na+ and K+ cations with varying concentrations over the self-photorechargeability of Pt/MoO3-driven system, it was revealed that the K+ electrolyte at a low concentration of 0.01 M resulted in the highest charge density of 22.89 mC/cm2. Other H+ and Na+ cations and concentrations are unfavourable due to the potentiality in inducing structural distortment as well unparallel rates of charging and discharging in the Pt/MoO3-driven system. Finally, DFT was simulated and the calculated binding energies (Eads) between the studied cations with the Pt/MoO3 crystalline framework validated the experimental finding.

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Abstract:

In this study, a novel interfaced photoanode of silver/silver orthophosphate (Ag/Ag3PO4) was synthesised via the controlled oxidation of Ag foil which resulted in a top porous layer of {111} facets-bounded Ag3PO4 tetrahedrons layer. This was achieved through a systematic understanding and optimisation of the critical synthesis parameters, including: concentration ratio of polyvinylpyrrolidone (PVP) used as the capping agent to precursor (C/P), volume ratio of hydrogen peroxide (H2O2) to deionised water (H2O) (H2O2:H2O) and reaction time. It was revealed that the best-performing Ag/Ag3PO4 interfaced photoanode can be synthesised at the C/P ratio of 4, H2O2:H2O ratio of 3:5 and reaction time of 20 h. This is owing to the synergistic reaction of Ag foil, NaH2PO4 and H2O2 under the assistance of PVP, which leads to the formation of the porous layer of highly reactive {111} facets-bounded Ag3PO4 tetrahedron structures. The optimised Ag/Ag3PO4 interfaced photoanode achieved an unprecedentedly high photocurrent density of 4.19 mA/cm2 at 1 V vs Ag/AgCl with an accompanying measured H2 evolution rate of 49.08 µmol/h cm2. Additionally, the applied bias photon-to-current efficiency (ABPE) and incident photon-to-current efficiency (IPCE) for the Ag/Ag3PO4 interfaced photoanode were recorded at 0.55% (0.84 V vs Ag/AgCl) and 56.5% (1 V vs Ag/AgCl, 410 nm), respectively.

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Abstract:

Geographic isolation limits energy access in remote Philippine islands. Among the few islands electrified, most are powered by diesel, a costly and unsustainable electricity source. Efforts on energy access should therefore consider affordable and sustainable renewable energy (RE) technologies. In this study, we simulated solar photovoltaic (PV) and wind power integration in 147 diesel-powered Philippine off-grid areas. Different configurations of solar PV, wind turbines, lithium-ion batteries, and diesel generators were evaluated based on levelized electricity costs and RE shares. The simulations show that solar PV should be utilized in all areas considered and wind power in 132 areas to guarantee reliable and continuous energy access with minimal costs. The hybrid energy systems have an average electricity cost of USD 0.227/kWh, an average RE share of 58.58 %, and a total annual savings of 108 million USD. The sensitivity analysis also shows that dependence on solar and wind power in Philippine off-grid islands is robust against uncertainties in component costs and electricity demand. With the promising off-grid solar PV and wind power potential in the country, policies that support RE-based hybrid grids should be implemented to address the trilemma of energy security, equity, and sustainability.

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Abstract:

The Philippines is home to thousands of off grid islands that are too distant from the mainland and consequently expensive to connect to the main grid. These islands are typically powered by diesel generators, which will require more subsidies as fuel costs continue to increase. Hybrid renewable energy systems (HRES) are an alternative energy source with lower reliance on fuel and generation costs. In this work, the financial sustainability of deploying HRES in Philippine off grid islands of various sizes was evaluated. Patongong Island, Lapinigan Island, Balabac Island, and Sibuyan Island were selected as case studies as their peak electrical demand varies from 4.4 kW in Patongong Island to 3.2 MW in Sibuyan Island, representing a large fraction of off-grid islands in the country. HRES consisting of solar photovoltaics, wind turbines, lithium ion batteries, and diesel generators in these islands were modeled in Island Systems LCOEmin Algorithm (ISLA), an in house energy systems modeling tool. Profitability metrics, such as the net present value, internal rate of return (IRR), and payback period (PBP), were then calculated at varying electricity prices. The large Sibuyan island was already profitable at 0.2 USD/kWh, comparable to the mainland rate, which suggests that subsidies in large islands can be removed. The low 11 % IRR and 13 year PBP may not be attractive to private investors, but this may be alleviated by raising electricity prices. Other islands, however, will still require subsidies as the small Patongong Island becomes profitable only at 1.5 times the mainland rate. This work encourages private sector participation by providing financial insights absent in many techno economic studies. Moreover, this study enlightens the public sector about the necessity of subsidies for providing energy access in small off grid islands.

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This study aimed to systematically evaluate and determine the specific roles of reactive oxygen species (ROS) and Zn2+ ions in governing the antibacterial properties of different ZnO nanoarchitectures. This could differ greatly on model bacteria under different irradiation conditions and affects on the design and scale-up of ZnO-based photocatalytic system for wastewater applications. Various ZnO nanostructures were synthesized, characterised and systematically evaluated for their antibacterial properties on both Gram-positive and Gram-negative bacteria under dark, UV-light, and simulated solar irradiation conditions. Results showed that the 1D-ZnO nanorods possessed the highest photo-deactivation ability with a 3.5-log reduction for B. subtilis and a 4.2-log reduction for E. coli under UV light conditions. This is precisely linked to the 1D rod-like ZnO nanostructures with a higher exposed polar surface that favours the dissolution kinetics of Zn2+ ions. Besides, the surface oxygen vacancies were found to be strongly correlated to the intracellular ROS concentration that imparts bactericidal effect at different extents depending on the ZnO nanostructures used. The photo-deactivation kinetics were found to be best-fitted using the empirical Hom model, as it could represent the non-linear bacterial inactivation kinetics profile with a prolonged tailing characteristic. Finally, the Friedman non-parametric test showed that all experimental datasets for B. subtilis and E. coli surviving cases were significantly different (p-value < 0.05). The post-hoc approach indicated that the Zn2+ ions dissolution was the fundamental factor in dictating the antibacterial properties in different ZnO nanostructures.

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Abstract:

The shipping industry is vital for archipelagic countries like the Philippines as they allow transport between islands, but it is a notable contributor of greenhouse gases. In this work, a framework for analyzing the techno-economic potential of hybridizing a sea vessel with solar photovoltaics, lithium-ion batteries, and diesel generators was presented. The roll on/roll off vessel Filipinas Ozamis was considered as a case study due to its commercial use. A 3D model of the roll-on/roll-off vessel was used to measure the ship’s dimensions. The load profile of the vessel was estimated from the ship’s dimensions, operational profile, route, and speed according to the MarineTraffic AIS database. Afterwards, diesel-only and hybrid energy systems were sized in HOMER Pro to power the electrified ship while minimizing its costs and noting the available space on the sea vessel. Lastly, the profitability of the hybrid energy system was determined. The hybrid system was marked with increased capital costs, but the fuel consumption and CO2 emissions were 18.50 % and 27.90 % lower than those of the diesel-only system, respectively. The hybrid system also had lower generation costs and 23.64 % higher net present value than the diesel-only system. This framework can be used in the absence of measured load profiles and can be extended to other sea vessels to conduct a national techno-economic assessment of hybridizing the country’s maritime industry.

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Abstract:

Battery energy storage systems are essential for stabilizing the intermittent power generation of renewable energy (RE) technologies. Their integration into RE systems is typically studied using energy systems modeling software that utilize either idealized models or complex models that require experimental data. Reduced order modeling offers minimal experimental costs through the use of a multiphysics model in lieu of experimental battery data. In this work, a previously reported multiphysics model of a lithium ion lithium iron phosphate (Li ion LFP) battery was simulated in COMSOL Multiphysics® and reduced into an equivalent circuit model (ECM). The reduced order ECM was then implemented as a battery systems model in an energy systems modeling tool to perform RE-based hybridization studies. Techno economic case studies were conducted on RE based systems powering a household and an off grid island to validate the reduced order ECM with the idealized battery model with HOMER Pro. Optimal component sizes computed using the two software generally showed good agreement and deviations were attributed to electrical losses. The state of charge (SOC) vs. time graphs generated by the two software had an average root mean square error of 0.00173 SOC units across the different case studies. Discrepancies were observed during rapid charging or high SOC values, which were characteristic of the reduced order ECM. This model reduction framework can be applied to other energy storage and conversion technologies, such as other Li ion chemistries, fuel cells, and supercapacitors, to generate chemistry specific models for energy systems research.

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Abstract: 

The increasing demand for batteries’ application in grid-balancing, electric vehicles, and portable electronics has prompted research efforts on improving their performance and safety features. The improvement of batteries involves the comparison of multiple battery designs and the determination of electrochemical and thermal property distributions at the continuum scale. This is achieved by using multiphysics modeling for investigatory battery research, as conventional experimental approaches would be costly and impractical. The fundamental electrochemical models for these batteries have been established, hence, new models are being developed for specific applications, such as thermal runaway and battery degradation in lithium-ion batteries, gas evolution in lead-acid batteries, and vanadium crossover in vanadium redox flow batteries. The inclusion of new concepts in multiphysics modeling, however, necessitates the consideration of phenomena beyond the continuum scale. This work presents a comprehensive review on the multiphysics models of lithium-ion, lead-acid, and vanadium redox flow batteries. The electrochemical models of these chemistries are discussed along with their physical interpretations and common applications. Modifications of these multiphysics models for adaptation and matching to end applications are outlined. Lastly, we comment on the direction of future work with regards to the interaction of multiphysics modeling with modeling techniques in other length and time scales. Molecular-scale models such as density functional theory and kinetic Monte Carlo can be used to create new multiphysics models and predict transport property correlations from first principles. Nanostructures and pore-level geometries can be optimized and integrated into continuum-scale models. The reduction of multiphysics models via machine learning, mathematical simplification, or regression enables their application in battery management systems and energy systems modeling.

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Abstract:

Geographic isolation limits energy access in remote Philippine islands. Among the few islands electrified, most are powered by diesel, a costly and unsustainable electricity source. Efforts on energy access should therefore consider affordable and sustainable renewable energy (RE) technologies. In this study, we simulated solar photovoltaic (PV) and wind power integration in 147 diesel-powered Philippine off-grid areas. Different configurations of solar PV, wind turbines, lithium-ion batteries, and diesel generators were evaluated based on levelized electricity costs and RE shares. The simulations show that solar PV should be utilized in all areas considered and wind power in 132 areas to guarantee reliable and continuous energy access with minimal costs. The hybrid energy systems have an average electricity cost of USD 0.227/kWh, an average RE share of 58.58 %, and a total annual savings of 108 million USD. The sensitivity analysis also shows that dependence on solar and wind power in Philippine off-grid islands is robust against uncertainties in component costs and electricity demand. With the promising off-grid solar PV and wind power potential in the country, policies that support RE-based hybrid grids should be implemented to address the trilemma of energy security, equity, and sustainability.

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Abstract:

This paper considers off-grid microgrids (MGs) from the Philippine archipelago and analyses their energy generation in differents aspects. Seven different energy clusters are used, representing realistic configurations and renewable energy shares. A Robust Model Predictive Control (MPC) framework is used for the energy management and coordination task of these island MGs. The MPC is based on a min./max. optimization procedure, which takes into account the whole uncertainty set. The reliability of the MG operations are analysed with respect to the different clusters; this evaluation is conducted using µ-analysis, performed with respect to the baseline model and the uncertainty set. The demand-side compliance of the MG is also investigated, with respect to stochastic behaviours of the demands and of the renewable sources (wind and solar). Numerical simulation results are presented in order to demonstrate that reliable power outlets are produced despite variation in renewables and of the demands. This paper offers a thorough analysis of simple energy system coordinated via MPC, showing how this method can indeed be used for renewable MG management, offering robustness and ensuring reliability.

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Abstract:

The electrical double layer (EDL) structure and interfacial interactions are studied to illustrate the influence of alkali metal (AM) cations on alkaline oxygen evolution reaction (OER). The electrochemical measurements show that the OER activity both on IrOx and NiCo2O3 increases in the sequence of Li+ < Na+ < Cs+ < K+ mainly due to the various interaction strength of specifically adsorbed OHad intermediates and non-specifically adsorbed AM+ad in the EDL. In particular, K+ breaks the limitation of the adsorbate’s linear scaling relation and enables a lattice-oxygen-mediated mechanism, resulting in activity enhancement. Further, based on our investigation, new strategies are proposed to synthesize Ir-Co oxide with modifications of various AM elements, such as Li, Na and K. The K-assisted Ir0.6Co0.4 amorphous oxide exhibits outstanding OER performance, i.e. 290 mV overpotential (without ohmic correction) at 10 mA cm2, and 36.9 mV dec-1 kinetic Tafel slope. The oxide modification with potassium plays a crucial role for its superior performance, which highlights the importance of the interfacial engineering to facilitate the electron transfer reactions.

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Abstract:

Developing durable electrocatalyst for oxygen reduction reaction (ORR) is essential for fuel cell commercialization. Herein, we perform a study of platinum-carbon (Pt/C) degradation mechanisms using potential cycling of accelerated durability testing protocols in acidic and alkaline media. Physicochemical results indicate that carbon surface oxides are formed after high-potential cycling in acid causing an increase in the double-layer capacitance and severe ORR activity loss due to Pt poisoning. Whereas, low-potential cycling in acid shows less ORR activity loss, mainly caused by Pt Ostwald ripening, and does not lead to a significant change in double-layer capacitance. In alkaline, the Pt/C catalyst after high-potential cycling shows a decrease of double-layer capacitance over time because of carbon layer dissolution. TEM images reveal larger Pt agglomerates in alkaline, due to high Pt mobility. These findings provide new insights into the role of catalyst and carbon support interface in developing mitigation strategies for stable fuel cell operation.

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Abstract:

Renewable energy (RE) utilization is expected to increase in the coming years due to its decreasing costs and the mounting socio-political pressure to decarbonize the world’s energy systems. On the other hand, lithium-ion (Li-ion) batteries are on track to hit the target 100 USD/kWh price in the next decade due to economy of scale and manufacturing process improvements, evident in the rise in Li-ion gigafactories. The forecast of RE and Li-ion technology costs is important for planning RE integration into existing energy systems. Previous cost predictions on Li-ion batteries were conducted using conventional learning curve models based on a single factor, such as either installed capacity or innovation activity. A two-stage learning curve model was recently investigated wherein mineral costs were taken as a factor for material cost to set the floor price, and material cost was a major factor for the battery pack price. However, these models resulted in the overestimation of future prices. In this work, the future prices of Li-ion nickel manganese cobalt oxide (NMC) battery packs – a battery chemistry of choice in the electric vehicle and stationary grid storage markets – were projected up to year 2025 using multi-factor learning curve models. Among the generated models, the two-factor learning curve model has the most realistic and statistically sound results having learning rates of 21.18% for battery demand and 3.0% for innovation. By year 2024, the projected price would fall below the 100 USD/kWh industry benchmark battery pack price, consistent with most market research predictions. Techno-economic case studies on the microgrid applications of the forecasted prices of Li-ion NMC batteries were conducted. Results showed that the decrease in future prices of Li-ion NMC batteries would make 2020 and 2023 the best years to start investing in an optimum (solar photovoltaic + wind + diesel generator + Li-ion NMC) and 100% RE (solar photovoltaic + wind + Li-ion NMC) off-grid energy system, respectively. A hybrid grid-tied (solar photovoltaic + grid + Li-ion NMC) configuration is the best grid-tied energy system under the current net metering policy, with 2020 being the best year to deploy the investment.

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Abstract:

Biodegradable primary batteries, also known as transient batteries, are essential to realize autonomous biodegradable electronic devices with high performance and advanced functionality. In this work, magnesium, copper, iron, and zinc ‐ metals that exist as trace elements in the human body ‐ were tested as materials for biomedical transient electronic devices. Different full cell combinations of Mg and X (where X = Cu, Fe, and Zn and the anodized form of the metals) with phosphate buffered saline (PBS) as electrolyte were studied. To form the cathodes, metal foils were anodized galvanostatically at a current density of 2.0 mA cm⁻² for 30 mins. Electrochemical measurements were then conducted for each electrode combination to evaluate full cell battery performance. Results showed that the  Mg−Cuanodized chemistry has the highest power density at 0.99 mW/cm2. Nominal operating voltages of 1.26 V for the first 0.50 h and 0.63 V for the next 3.7 h were observed for Cuanodized which was discharged at a current density of 0.70 mA cm-2. Among the materials tested Cuanodized exhibited the best discharge performance with an average specific capacity of 2.94 mAh cm-2, which is comparable to previous reports on transient batteries.

Abstract:

Transition towards sustainable energy systems is of utmost importance to avert global consequences of climate change. Within the framework of the Paris Agreement and Marrakech Communique, this study analyses an energy transition pathway utilising renewable resources for the Philippines. The transition study is performed from 2015 to 2050 on a high temporal and spatial resolution data, using a linear optimisation tool. From the results of this study, technically, a 100% fossil free energy system in 2050 is possible, with a cost structure comparable to an energy system in 2015, while having zero greenhouse gas emissions. Solar PV as a generation and batteries a as storage technology form the backbone of the energy system during the transition. Direct and indirect electrification across all sectors would result in an efficiency gain of more than 50% in 2050, while keeping the total annual investment within 20‐55 b€. Heat pumps, electrical heating, and solar thermal technologies would supply heat, whereas, direct electricity and synthetic fuels would fuel the energy needs of the transport sector. The results indicate that, indigenous renewable resources in the Philippines could power the demand from all energy sectors, thereby, bringing various socio-economic benefits.

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Here, we synthesize a functional MoO3 photoanode with self-photorechargeability through aerosol-assisted chemical vapour deposition. The role of platinum co-catalyst in Pt-mediated MoO3 photoanode (Pt/MoO3) was investigated to improve and maintain its charge density to enable photoelectrochemical water oxidation under non-irradiated condition. Raman spectroscopy and X-ray diffraction analyses showed that the orthorhombic phase of MoO3 was formed with significant Raman diffraction peaks and crystal planes were grown in the (0k0) crystallographic orientation for better charge storage capacity in MoO3 photoanodes, respectively. Furthermore, the chronoamperometry measurements of the Pt/MoO3 photoanode revealed that both current and charge densities were improved by 29 times and 94 times, respectively, than the bare MoO3 photoanode. This is attributed to the presence of Pt co-catalyst, which acts as an effective electron sink in inhibiting the recombination of photogenerated charge carriers. A density functional theory simulation was then used to validate the experimental findings and fundamental mechanisms of self-photorechargeability in Pt/MoO3 photoanodes. It was found that the distinct characteristic of slow decay in charge density of Pt/MoO3 photoanode is due to the formation of alkali cation/metal layer, where the intercalated photogenerated electrons require a higher energy to overcome the energetic barrier of the alkali cation/metal layer.

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Novel cellulose acetate-based anion exchange membranes (CA-AEM) are successfully synthesized via gamma radiation grafting as a possible renewable alternative to commercial AEMs. Using CA film precursors with degree of acetylation of 2.5, the synthesized AEM shows a high ion exchange capacity of 2.15 mmol g-1 obtained at high degree of grafting of 45%. It was determined using thermogravimetric analysis that the radiation-grafted CA-AEM has stable amine functional groups under oxygen environment within the normal operating temperature range of alkaline fuel cells. The CA-AEM also exhibits appreciable performance over a range of temperatures, with a highest ionic conductivity of up to 0.163 S cm-1 depending on the synthesis parameters. Results revealed that membranes prepared using gamma radiation dose of 31 kGy and- above are susceptible to mechanical and dimensional instability due to increased water uptake and degree of swelling. Further study should consider the balance between grafting parameters and the desired hydrophysical properties.

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Abstract:

Renewable energy (RE) utilization is expected to increase in the coming years due to its decreasing costs and the mounting socio-political pressure to decarbonize the world’s energy systems. On the other hand, lithium-ion (Li-ion) batteries are on track to hit the target 100 USD/kWh price in the next decade due to economy of scale and manufacturing process improvements, evident in the rise in Li-ion gigafactories. The forecast of RE and Li-ion technology costs is important for planning RE integration into existing energy systems. Previous cost predictions on Li-ion batteries were conducted using conventional learning curve models based on a single factor, such as either installed capacity or innovation activity. A two-stage learning curve model was recently investigated wherein mineral costs were taken as a factor for material cost to set the floor price, and material cost was a major factor for the battery pack price. However, these models resulted in the overestimation of future prices. In this work, the future prices of Li-ion nickel manganese cobalt oxide (NMC) battery packs – a battery chemistry of choice in the electric vehicle and stationary grid storage markets – were projected up to year 2025 using multi-factor learning curve models. Among the generated models, the two-factor learning curve model has the most realistic and statistically sound results having learning rates of 21.18% for battery demand and 3.0% for innovation. By year 2024, the projected price would fall below the 100 USD/kWh industry benchmark battery pack price, consistent with most market research predictions. Techno-economic case studies on the microgrid applications of the forecasted prices of Li-ion NMC batteries were conducted. Results showed that the decrease in future prices of Li-ion NMC batteries would make 2020 and 2023 the best years to start investing in an optimum (solar photovoltaic + wind + diesel generator + Li-ion NMC) and 100% RE (solar photovoltaic + wind + Li-ion NMC) off-grid energy system, respectively. A hybrid grid-tied (solar photovoltaic + grid + Li-ion NMC) configuration is the best grid-tied energy system under the current net metering policy, with 2020 being the best year to deploy the investment.

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The industrial sector is a major contributor to the economic growth of the Philippines. However, it is also one of the top consumers of energy, which is produced mainly from fossil fuels. The Philippine industrial sector must therefore be supported economically while minimizing the emissions associated with energy consumption. A potential strategy for minimizing costs and emissions is the installation of solar photovoltaic (PV) modules on the rooftops of industrial facilities, but this approach is hindered by existing energy policies in the country. In this work, we performed a techno-economic assessment on the implementation of rooftop solar PV in Philippine industrial facilities under different policy scenarios. Our study considered 139 randomly sampled industrial plants under MERALCO franchise area in the Philippines. Under the current net metering policy, 132 of the evaluated facilities were economically viable for the integration of rooftop solar PV. This corresponds to an additional 1035 MWp of solar PV capacity and the avoidance of 8.4 million tons of CO2 emissions with minimal financial risk. In comparison, an expanded net metering policy supports the deployment of 4653 MWp of solar PV and the avoidance of 38 million tons of CO2. By enabling an enhanced net metering policy, the widespread application of rooftop solar PV may present considerable savings and emission reduction for energy-intensive industries (electrical and semiconductors, cement and concrete, steel and metals, and textile and garments) and lower generation costs for less energy intensive industries (construction and construction materials, transportation and logistics, and food and beverages).

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Activated carbon-nickel (II) oxide (AC-NiO) electrodes were studied as materials for the capacitive deionization (CDI) of aqueous sodium chloride solution. AC-NiO electrodes were fabricated through physical mixing and low-temperature heating of precursor materials. The amount of NiO in the electrodes was varied and its effect on the deionization performance was investigated using a single-pass mode CDI setup. The pure activated carbon electrode showed the highest specific surface area among the electrodes. However, the AC-NiO electrode with approximately 10 and 20% of NiO displayed better deionization performance. The addition of a dielectric material like NiO to the carbon material resulted in the enhancement of the electric field, which eventually led to an improved deionization performance. Among all as-prepared electrodes, the AC-NiO electrode with approximately 10% of NiO gave the highest salt adsorption capacity and charge efficiency, which are equal to 7.46 mg/g and 90.1%, respectively. This finding can be attributed to the optimum enhancement of the physical and chemical characteristics of the electrode brought by the addition of the appropriate amount of NiO.

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Philippine off-grid islands are mostly electrified by diesel generators, resulting in costly electricity that is interrupted by fuel supply disruptions. The archipelagic nature of the country also impedes off-grid electrification due to the high capital cost of grid extension. Transitioning from diesel-only systems to hybrid renewable energy systems and interconnecting the island microgrids can solve these problems while promoting cleaner energy production. In this work, a comparative study on decentralized and clustered hybrid renewable energy system microgrids in the Polillo group of islands in the Philippines, using HOMER Pro, was performed. Microgrids comprising solar photovoltaics, lithium-ion battery energy storage, and diesel generators were designed on each island. Clustered systems encompassing multiple islands in the island group were simulated by also considering the least-cost interconnection paths. The techno-economics of each decentralized or clustered system and the four-island system were evaluated based on the levelized cost of electricity (LCOE). Reliability was assessed using the change in LCOE upon the failure of a component and during weather disturbances. Transitioning from diesel-only systems to hybrid systems reduces generation costs by an average of 42.01% and increases the renewable energy share to 80%. Interconnecting the hybrid systems results in an average increase of 2.34% in generation costs due to the cost of submarine cables but improves system reliability and reduces the optimum solar photovoltaic and lithium-ion storage installations by 6.66% and 8.71%, respectively. This research serves as a framework for the interconnection pre-feasibility analysis of other small off-grid islands.

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Abstract:

Several confirmed cases of arsenic (As) poisoning have been reported in Central Luzon, the Philippines, in recent years. There is a growing interest in As research in the Philippines due to the reported As poisoning cases. However, an extensive spatiotemporal As study has not been conducted. In this work, As concentration measurements were conducted in 101 wells in Guagua, Pampanga, in Central Luzon, the Philippines, from November 2018 to November 2019. The wells included 86 public hand pumps, 10 pumping stations, and 5 private, jet-powered pumps. Using hydride generation—inductively coupled plasma—optical emission spectroscopy (HG-ICP-OES), analysis of the wells in 12 barangays in Guagua revealed that 38.7% had average As concentrations beyond the 10 ppb limit with some wells having high Mn (4.0 ppm) and Fe (2.0 ppm) content as well. The high pH and reducing conditions in the wells in Guagua may have contributed to the persistence of As in the groundwater. The mean difference in wet season versus dry season As measurements were -4.4 (As < 10 ppb), -13.2 (10 to 50 ppb As), -27.4 (As > 50 ppb). Eighty-three wells (82.2%) had higher As concentrations in the dry season, 8 wells (7.92%) had higher As concentrations in the wet season, 7 wells (6.93%) had no significant difference between the wet and dry season, and 3 wells had been decommissioned. These results indicate that there is a significant difference in As concentrations in the wet and dry seasons, and this could have implications in water treatment technology and policy implementation. The work resulted in the first year-long characterization of groundwater As in the Philippines.

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Abstract:

Arsenic (As) is a naturally occurring element in the environment that poses significant risks to human health. Several treatment technologies have been successfully used in the treatment of As-contaminated waters. However, limited literature has explored advanced electrocoagulation (EC) processes for As removal. The present study evaluates the As removal performance of electrocoagulation, electrochemical peroxidation (ECP), and photo-assisted electrochemical peroxidation (PECP) technologies at circumneutral pH using electroactive iron electrodes. The influence of As speciation and the role of oxidants in As removal were investigated. We have identified the ECP process to be a promising alternative for the conventional EC with around 4-fold increase in arsenic removal capacity at a competitive cost of 0.0060 $/m3. Results also indicated that the rate of As(III) oxidation at the outset of electrochemical treatment dictates the extent of As removal. Both ECP and PECP processes reached greater than 96% As(III) conversion at 1 C/L and achieved 86% and 96% As removal at 5 C/L, respectively. Finally, the mechanism of As(III) oxidation was evaluated, and results showed that Fe(IV) is the intermediate oxidant generated in advanced EC processes, and the contribution of ●OH brought by UV irradiation is insignificant.

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Abstract:

Destructive weather extremes ‐ the key impacts of the climate emergency ‐ acutely signal the need to increase the resiliency, especially of climate-vulnerable islands and its peoples. “Islands” are detached communities that are either geographically bounded by water or are metaphors for inland off-grid villages. The extant literature on resilient infrastructures is rich, but this corpus is mostly concentrated on food and water systems, security, and transport. Making energy systems resilient in islands, this paper argues, is equally important. In these island energy systems, resilience can be achieved by regarding them as sociotechnical assemblages where engineering innovation is co-produced alongside social and institutional shifts. This article suggests that resilient energy systems in islands can be checked against their explicit characteristics as a system condition, as a set of processes, and as a set of outcomes. Understanding power relations and ethical concerns are also important. To illustrate these characteristics, case studies from Romblon in the Philippines (a geographic island) and Petchaburi in Thailand (a metaphorical island) are provided. There is no perfect resilient island energy systems, but these illustrations show that they can be pursued.

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Abstract:

The electrooxidation kinetics of ethanol is key to making direct ethanol fuel cells and electrocatalytically reforming ethanol viable technologies for a more sustainable energy conversion. In this study, the electrooxidation of ethanol was investigated on nickel hydroxide (Ni(OH)2) catalysts synthesized using a facile solvothermal method. Variations in the temperature, heating time, and the addition of oleylamine in the precursor enabled the phase and morphology control of the catalysts. X-ray diffraction and scanning electron microscopy show that the addition of oleylamine in the precursor resulted in microspheres with a high surface area, but favored the formation of β-phase Ni(OH)2. Elevated temperatures or prolonged periods of heating in a controlled environment, on the other hand, can lead to the formation of the ethanol oxidation reaction-active α-phase. Among the synthesized catalysts, the α-Ni(OH)2 microspheres with nanoflakes achieved the highest activity for ethanol oxidation with a current density of 24.4 mA cm2 at 1.55 V (vs. RHE, reversible hydrogen electrode) in cyclic voltammetry tests and stable at 40 mA cm2 in chronoamperometric tests at the same potential, comparatively higher than other Ni-based catalysts found in the literature. While the overpotential is beyond the useful range for direct ethanol fuel cells, it may be useful for understanding the mechanism of ethanol oxidation reactions on transition metal hydroxides at their oxidizing potential for ethanol electroreforming.

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Abstract:

There is a growing research interest in exploring the self-photorechargeability of photoanodes, which enables photoelectrochemical (PEC) water oxidation even under non-irradiated conditions. The main aim of this study was to develop a facile synthesis of molybdenum trioxide (MoO3) photoanode displaying self-photorechargeability using an aerosol-assisted chemical vapour deposition (AA-CVD) method. A systematic optimisation of the key synthesis parameters of AA-CVD method, namely: (1) ultrasonication time of precursor solution, and (2) annealing temperature was carried out in order to understand the best trade-off between photocurrent density (illuminated conditions) and charge density (non-illuminated conditions). Field emission-scanning electron microscopy images showed that the MoO3 photoanodes synthesized via AA-CVD method exhibited a 3D plate-like crystalline structure that gave a large voltammogram area, indicating that the MoO3 photoanodes possessed high charge storage capacity for photogenerated electrons. PEC measurements showed that the optimised MoO3 photoanode obtained during an ultrasonication time of 25 min and at the annealing temperature of 500 ℃ achieved a photocurrent density of 1.47 µcm2 at 1.0 V vs Pt electrode. A significantly prolonged on-off illumination cycle (i.e. 1000 s) showed a significant storage capacity of photogenerated electrons within the 3D plate-like MoO3 crystalline structure was discharged during the non-irradiated conditions, and a charge density of 0.35 mC/cm2.

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Abstract:

In this study, we performed density functional theory based calculations to determine the effect of the size of Cux (x = 1 (adatom), 3 (trimer), 7 (heptamer)) clusters supported on Cu(111) toward the adsorption of CO, O, and CO2, and the dissociation of CO2. CO adsorbs with comparable adsorption energies on the different cluster systems, which are influenced by the reactivity of the Cu atoms in the cluster and the interaction of CO with the Cu atoms in the terrace. The O atom, on the other hand, will always favor to adsorb on hollow sites and is more stable on the hollow sites of smaller clusters. CO2 dissociates with lower activation energy on the cluster region than on flat Cu(111). We obtained the lowest activation energy on Cu3 due to its more reactive Cu atoms than the Cu7 case and due to the possibility of O to adsorb on the cluster region, which is not observed in the Cu1 case. The presented results will provide insights on future studies on supported cluster systems and their possible use as catalysts for CO2-related reactions.

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Abstract:

The flow field is an integral part of a proton exchange membrane fuel cell. In this work, three flow-field designs, including straight parallel, multiple channel serpentine, and single channel serpentine, are studied systematically to investigate their effects on fuel cell performance. To evaluate the characteristics of each design, relative humidity and flow rate are parametrically adjusted to evaluate performance experimentally. A finite element-based 3D steady state, single phase COMSOL computational model is employed to analyze reactant distribution and fuel cell performance. The single channel serpentine exhibits the best performance under the greatest variety of operating conditions, but also experiences the highest inlet-outlet pressure differentials. This study shows that parallel channel design has more evenly distributed reactant concentration, but is prone to liquid water accumulation, which requires high flow rate to remain stable operation under wet conditions. In summary, the multiple channel serpentine design can provide a reasonable balance between pressure drop and flow distribution with robust fuel cell operation.

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Abstract:

Freshwater in off-grid islands is sourced from rain, groundwater, or mainland imports, which are unreliable, limited, and expensive, respectively. Sustainable freshwater generation from desalination of abundant seawater is another alternative worth exploring. Model-based techno-economic simulations have focused on reverse osmosis desalination due to its low energy consumption and decreasing costs. However, reverse osmosis requires frequent and costly membrane replacement. Other desalination technologies have advantages such as less stringent feedwater requirements, but detailed studies are yet to be done. In this work, a techno-economic comparison of multi-effect distillation, multi-stage flash, mechanical vapor compression, and reverse osmosis coupled with solar photovoltaic-lithium ion-diesel hybrid system was performed by comparing power flows to study the interaction between energy and desalination components. Optimization with projected costs were then performed to investigate future trends. Lastly, we used stochastic generation and demand profiles to infer uncertainties in energy and desalination unit sizing. Reverse osmosis is favorable due to low energy and water costs, as well as possible compatibility with renewable energy systems. Multi-effect distillation and multi-stage flash may also be advantageous for low-risk applications due to system robustness.

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Abstract:

Sluggish kinetics in oxygen reduction reaction (ORR) requires low-cost and highly durable electrocatalysts ideally produced from facile methods. In this work, we explored the conversion and utilization of waste biomass as potential carbon support for α-MnO2 catalyst in enhancing its ORR performance. Carbon supports were derived from different waste biomass via hydrothermal carbonization (HTC) at different temperature and duration, followed by KOH activation and subsequent heat treatment. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDX) and X-Ray diffraction (XRD) were used for morphological, chemical, and structural characterization, which revealed porous and amorphous carbon supports for α-MnO2. Electrochemical studies on ORR activity suggest that carbon-supported α-MnO2 derived from HTC of corncobs at 250 ℃ for 12 h (CCAC + MnO2 250-12) gives the highest limiting current density and lowest overpotential among the synthesized carbon-supported catalysts. Moreover, CCAC + MnO2 250-12 facilitates ORR through a 4-e– pathway, and exhibits higher stability compared to VC + MnO2 (Vulcan XC-72) and 20% Pt/C. The synthesis conditions preserve oxygen functional groups and form porous structures in corncobs, which resulted in a highly stable catalyst. Thus, this work provides a new and cost-effective method of deriving carbon support from biomass that can enhance the activity of α-MnO2 towards ORR.

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Abstract:

This study aimed to evaluate the impacts of morphological-controlled ZnO nanoarchitectures on aerobic microbial communities during real wastewater treatment in an aerobic-photocatalytic system. Results showed that the antibacterial properties of ZnO nanoarchitectures were significantly more overwhelming than their photocatalytic properties. The inhibition of microbial activities in activated sludge by ZnO nanoarchitectures entailed an adverse effect on wastewater treatment efficiency. Subsequently, the 16S sequencing analysis were conducted to examine the impacts of ZnO nanoarchitectures on aerobic microbial communities, and found the significantly lower microbial diversity and species richness in activated sludge treated with 1D-ZnO nanorods as compared to other ZnO nanoarchitectures. Additionally, 1D-ZnO nanorods reduced the highest proportion of Proteobacteria phylum in activated sludge due to its higher proportion of active polar surfaces that facilitates Zn2+ ions dissolution. Pearson correlation coefficients showed that the experimental data obtained from COD removal efficiency and bacterial log reduction were statistically significant (p-value < 0.05), and presented a positive correlation with the concentration of Zn2+ ions. Finally, a non-parametric analysis of Friedman test and post-hoc analysis confirmed that the concentration of Zn2+ ions being released from ZnO nanoarchitectures is the main contributing factor for both the reduction in COD removal efficiency and bacterial log reduction.

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Abstract:

In this study, we reported on the successful fabrication of a novel heterojunction photocatalyst (in particulate system) with a Type II band alignment between 1D-ZnO nanorods and BiVO4 nanocrystals. Pristine 1D-ZnO nanorods and BiVO4 nanocrystals were first fabricated through hydrothermal reaction followed by heterojunction formation via the wet chemical reaction. The 1D-ZnO/xBiVO4 heterojunction photocatalyst (x = weight ratio of BiVO4 in g) that found optimum when x = 0.08 g was used for the degradation of salicylic acid (SA) and Reactive Black 5 (RB5) resulting in high pseudo-first-order reaction rate constants of 0.0049 min 1 and 0.0132 min 1, respectively. Electrochemical studies proved that the 1D-ZnO/0.08BiVO4 heterojunction photocatalyst demonstrated a fast charge mobility and the most efficient photogenerated charge carriers separation among other heterojunction samples as analysed from PL spectra. Besides, UV‐vis spectroscopic measurement and optical characterisation showed that the improved photoactivity in 1D-ZnO/BiVO4 is attributed to the formation of a Type II heterojunction staggered arrangement that enables a broader visible-light harvesting ability. Finally, a postulation photocatalytic mechanism was proposed based on the theoretical band alignment diagram between the 1D-ZnO nanorods and BiVO4 nanocrystals as well as portraying the fundamental charge carriers transfer within the 1D-ZnO/BiVO4 heterojunction photocatalyst.

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Abstract:

While bulk zinc oxide (ZnO) is of non-toxic in nature, ZnO nanoarchitectures could potentially induce the macroscopic characteristics of oxidative, lethality and toxicity in the water environment. Here we report a systematic study through state-of-the-art controllable synthesis of multi-dimensional ZnO nanoarchitectures (i.e. 0D-nanoparticle, 1D-nanorod, 2D-nanosheet, and 3D-nanoflowers), and subsequent in-depth understanding on the fundamental factor that determines their photoactivities. The photoactivities of resultant ZnO nanoarchitectures were interpreted in terms of the photodegradation of salicylic acid as well as inactivation of Bacillus subtilis and Escherichia coli under UV-irradiation. Photodegradation results showed that 1D-ZnO nanorods demonstrated the highest salicylic acid photodegradation efficiency (99.4%) with a rate constant of 0.0364 min-1. 1D-ZnO nanorods also exhibited the highest log reductions of B. subtilis and E. coli of 3.5 and 4.2, respectively. Through physicochemical properties standardisation, an intermittent higher k value for pore diameter (0.00097 min-1 per mm), the highest k values for crystallite size (0.00171 min-1 per nm) and specific surface area (0.00339 min-1 per m2/g) contributed to the exceptional photodegradation performance of nanorods. Whereas, the average normalised log reduction against the physicochemical properties of nanorods (i.e. low crystallite size, high specific surface area and pore diameter) caused the strongest bactericidal effect.

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