Indispensable Nafion Ionomer for High-Efficiency and Stable Oxygen Evolution Reaction in Alkaline Media.

Addressing the challenge of sluggish kinetics and limited stability in alkaline oxygen evolution reactions, recent exploration of novel electrochemical catalysts offers improved prospects. To expedite the assessment of these catalysts, a half-cell rotating disk electrode is often favored for its simplicity. However, the actual catalyst performance strongly depends on the fabricated catalyst layers, which encounter mass transport overpotentials. We systematically investigate the role and sequence of electrode drop-casting methods onto a glassy carbon electrode regarding the efficiency of the oxygen evolution reaction. The catalyst layer without Nafion experiences nearly 50% activity loss post stability test, while those with Nafion exhibit less than 5% activity loss. Additionally, the sequence of application of the catalyst and Nafion also shows a significant effect on catalyst stability. The catalyst activity increases by roughly 20% after the stability test when the catalyst layer is coated first with an ionomer layer, followed by drop-casting the catalysts. Based on the half-cell results, the Nafion ionomer not only acts as a binder in the catalyst layer but also enhances the interfacial interaction between the catalyst and electrolyte, promoting performance and stability. This study provides new insights into the efficient and accurate evaluation of electrocatalyst performance and stability as well as the role of Nafion ionomer in the catalyst layer.

Borate-Based Compounds as Mixed Polyanion Cathode Materials for Advanced Batteries.

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.

Data on the techno-economic and financial analyses of hybrid renewable energy systems in 634 Philippine off-grid islands.

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].

Development of Magnesium Anode-Based Transient Primary Batteries.

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 Mg-Cuanodized which was discharged at a current density of 0.70 mA cm-2 . Among the materials tested, Mg-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.

Alkaline earth atom doping-induced changes in the electronic and magnetic properties of graphene: a density functional theory study.

Density functional theory was used to investigate the effects of doping alkaline earth metal atoms (beryllium, magnesium, calcium and strontium) on graphene. Electron transfer from the dopant atom to the graphene substrate was observed and was further probed by a combined electron localization function/non-covalent interaction (ELF/NCI) approach. This approach demonstrates that predominantly ionic bonding occurs between the alkaline earth dopants and the substrate, with beryllium doping having a variant characteristic as a consequence of electronegativity equalization attributed to its lower atomic number relative to carbon. The ionic bonding induces spin-polarized electronic structures and lower workfunctions for Mg-, Ca-, and Sr-doped graphene systems as compared to the pristine graphene. However, due to its variant bonding characteristic, Be-doped graphene exhibits non-spin-polarized p-type semiconductor behavior, which is consistent with previous works, and an increase in workfunction relative to pristine graphene. Dirac half-metal-like behavior was predicted for magnesium doped graphene while calcium doped and strontium doped graphene were predicted to have bipolar magnetic semiconductor behavior. These changes in the electronic and magnetic properties of alkaline earth doped graphene may be of importance for spintronic and other electronic device applications.

Cluster size effects on the adsorption of CO, O, and CO2 and the dissociation of CO2 on two-dimensional Cu x (x = 1, 3, and 7) clusters supported on Cu(111) surface: a density functional theory study.

In this study, we performed density functional theory based calculations to determine the effect of the size of Cu x (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.

Impacts of morphological-controlled ZnO nanoarchitectures on aerobic microbial communities during real wastewater treatment in an aerobic-photocatalytic system.

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.

Multi-dimensional zinc oxide (ZnO) nanoarchitectures as efficient photocatalysts: What is the fundamental factor that determines photoactivity in ZnO?

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-A 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.

Electrolyte-Dependent Oxygen Evolution Reactions in Alkaline Media: Electrical Double Layer and Interfacial Interactions.

Traditional understanding of electrocatalytic reactions generally focuses on either covalent interactions between adsorbates and the reaction interface (i.e., electrical double layer, EDL) or electrostatic interactions between electrolyte ions. Here, our work provides valuable insights into interfacial structure and ionic interactions during alkaline oxygen evolution reaction (OER). The importance of inner-sphere OH- adsorption is demonstrated as the IrOx activity in 4.0 M KOH is 6.5 times higher than that in 0.1 M KOH. Adding NaNO3 as a supporting electrolyte, which is found to be inert for long-term stability, complicates the electrocatalytic reaction in a half cell. The nonspecially adsorbed Na+ in the outer compact interfacial layer is suggested to form a stronger noncovalent interaction with OH- through hydrogen bond than adsorbed K+, leading to the decrease of interfacial OH- mobility. This hypothesis highlights the importance of outer-sphere adsorption for the OER, which is generally recognized as a pure inner-sphere process. Meanwhile, based on our experimental observations, the pseudocapacitive behavior of solid-state redox might be more reliable in quantifying active sites for OER than that measured from the conventional EDL charging capacitive process. The interfacial oxygen transport is observed to improve with increasing electrolyte conductivity, ascribing to the increased accessible active sites. The durability results in a liquid alkaline electrolyzer which shows that adding NaNO3 into KOH solution leads to additional degradation of OER activity and long-term stability. These findings provide an improved understanding of the mechanistic details and structural motifs required for efficient and robust electrocatalysis.

Interaction of CO, O, and CO2 with Cu cluster supported on Cu(1 1 1): a density functional theory study.

We performed density functional theory (DFT) based calculations to investigate the interaction of CO2 and its dissociated species (CO and O) on Cu3 cluster supported on Cu(1 1 1) (Cu3/Cu(1 1 1)) surfaces. Similar investigations were conducted on Cu(1 1 1) for purpose of comparison. In general, adsorption of CO and O are stronger on the cluster region than on the terrace region of Cu3/Cu and on the flat Cu surface. CO2, on the other hand, is weakly adsorbed on the surfaces. With reference to CO2 dissociation on Cu(1 1 1), we found that the cluster lowers the activation barrier and provides a more stable adsorption of the dissociated species. The presence of co-adsorbed CO in the cluster, however, will increase the activation energy. The variation in the activation barrier with the amount of CO is influenced by the stability of the O atom from the dissociated CO2. We further found that the adsorption energy of O atom is a possible descriptor for CO2 dissociation on the cluster region. The Cu cluster supported on Cu surface could be a promising catalyst for CO2 related reactions based on the lower activation energy for CO2 dissociation on the system than on Cu(1 1 1).

Electrode Architecture in Galvanic and Electrolytic Energy Cells.

Electrodes in galvanic and electrolytic energy cells are complicated structures comprising redox-active materials, ionic/electronic conductors, and porous pathways for mass transfer of reactants. In contrast to breakthroughs in component development, methods of optimizing whole-system architectural design to draw maximum output have not been well explored. In this Minireview, we introduce generalized types of electrode architecture, discuss fabrication strategies, and characterize already built structures. Systematic efforts to discover optimal electrode configurations will resolve long-standing discrepancies that arise between whole systems and the sums of their parts for a number of electrochemical reactions and technologies.

Improvement of Energy Capacity with Vitamin†C Treated Dual-Layered Graphene-Sulfur Cathodes in Lithium-Sulfur Batteries.

Invited for this month's cover is the groups of Prof. Dr. Jaeyoung Lee at the Gwangju Institute of Science and Technology in South Korea. The image shows that Vitamin C can be used to effectively improve the performance of lithium-sulfur batteries.

Improvement of Energy Capacity with Vitamin†C Treated Dual-Layered Graphene-Sulfur Cathodes in Lithium-Sulfur Batteries.

A graphene-based cathode design for lithium-sulfur batteries (LSB) that shows excellent electrochemical performance is proposed. The dual-layered cathode is composed of a sulfur active layer and a polysulfide absorption layer, and both layers are based on vitamin C treated graphene oxide at various degrees of reduction. By controlling the degree of reduction of graphene, the dual-layered cathode can increase sulfur utilization dramatically owing to the uniform formation of nanosized sulfur particles, the chemical bonding of dissolved polysulfides on the oxygen-rich sulfur active layer, and the physisorption of free polysulfides on the absorption layer. This approach enables a LSB with a high specific capacity of over 600 mAh gsulfur (-1) after 100 cycles even under a high current rate of 1C (1675 mA gsulfur (-1) ). An intriguing aspect of our work is the synthesis of a high-performance dual-layered cathode by a green chemistry method, which could be a promising approach to LSBs with high energy and power densities.

Controlled electrochemical etching of nanoporous Si anodes and its discharge behavior in alkaline Si-air batteries.

We report the fabrication of nanoporous silicon (nPSi) electrodes via electrochemical etching to form a porous Si layer with controllable thickness and pore size. Varying the etching time and ethanolic HF concentration results in different surface morphologies, with various degrees of electrolyte access depending on the pore characteristics. Optimizing the etching condition leads to well-developed nPSi electrodes, which have thick porous layers and smaller pore diameter and exhibit improved discharge behavior as anodes in alkaline Si-air cells in contrast to flat Si anode. Although electrochemical etching is effective in improving the interfacial characteristics of Si in terms of high surface area, we observed that mild anodization occurs and produces an oxide overlayer. We then show that this oxide layer in nPSi anodes can be effectively removed to produce an nPSi anode with good discharge behavior in an actual alkaline Si-air cell. In the future, the combination of high surface area nPSi anodes with nonaqueous electrolytes (e.g., room-temperature ionic liquid electrolyte) to minimize the strong passivation behavior and self-discharge in Si could lead to Si-air cells with a stable voltage profile and high anode utilization.

Insights into an autonomously formed oxygen-evacuated Cu2O electrode for the selective production of C2H4 from CO2.

Electrochemical conversion of carbon dioxide (CO2) to small organic fuels (e.g. formate, methanol, ethylene, ethanol) is touted as one of the most promising approaches for solving the problems of climate change and energy security. In this study, we report the highly efficient electrochemical reduction of CO2 using cuprous oxide (Cu2O) electrodes to produce ethylene (C2H4) primarily. During CO2 electrolysis using electrodeposited Cu2O on a carbon electrode, we observe the transformation of a compact metal oxide layer to a metal oxide structure with oxygen vacant sites at the bulk region. In contrast to previous studies, our results clearly indicate that Cu2O remains at the surface of the catalyst and it efficiently catalyzes the conversion process of CO2 at low overpotential, exhibiting a high selective faradaic efficiency of over 20% towards C2H4 formation even in long-term electrolysis.

Quasi-perpetual discharge behaviour in p-type Ge-air batteries.

Metal-air batteries continue to become attractive energy storage and conversion systems due to their high energy and power densities, safer chemistries, and economic viability. Semiconductor-air batteries - a term we first define here as metal-air batteries that use semiconductor anodes such as silicon (Si) and germanium (Ge) - have been introduced in recent years as new high-energy battery chemistries. In this paper, we describe the excellent doping-dependent discharge kinetics of p-type Ge anodes in a semiconductor-air cell employing a gelled KOH electrolyte. Owing to its Fermi level, n-type Ge is expected to have lower redox potential and better electronic conductivity, which could potentially lead to a higher operating voltage and better discharge kinetics. Nonetheless, discharge measurements demonstrated that this prediction is only valid at the low current regime and breaks down at the high current density region. The p-type Ge behaves extremely better at elevated currents, evident from the higher voltage, more power available, and larger practical energy density from a very long discharge time, possibly arising from the high overpotential for surface passivation. A primary semiconductor-air battery, powered by a flat p-type Ge as a multi-electron anode, exhibited an unprecedented full discharge capacity of 1302.5 mA h gGe(-1) (88% anode utilization efficiency), the highest among semiconductor-air cells, notably better than new metal-air cells with three-dimensional and nanostructured anodes, and at least two folds higher than commercial Zn-air and Al-air cells. We therefore suggest that this study be extended to doped-Si anodes, in order to pave the way for a deeper understanding on the discharge phenomena in alkaline metal-air conversion cells with semiconductor anodes for specific niche applications in the future.

Excavated Fe-N-C sites for enhanced electrocatalytic activity in the oxygen reduction reaction.

Platinum (Pt) is the best electrocatalyst for the oxygen reduction reaction (ORR) in hydrogen fuel cells, but it is an extremely expensive resource. The successful development of a cost-effective non-Pt ORR electrocatalyst will be a breakthrough for the commercialization of hydrogen-air fuel cells. Ball milling has been used to incorporate metal and nitrogen precursors into micropores of carbon more effectively and in the direct nitrogen-doping of carbon under highly pressurized nitrogen gas in the process of the preparation of non-noble ORR catalysts. In this study, we first utilize ball milling to excavate the ORR active sites embedded in Fe-modified N-doped carbon nanofibers (Fe-N-CNFs) by pulverization. The facile ball-milling process resulted in a significant enhancement in the ORR activity and the selectivity of the Fe-N-CNFs owing to the higher exposure of the metal-based catalytically active sites. The degree of excavation of the Fe-based active sites in the Fe-N-CNFs for the ORR was investigated with cyclic voltammetry, X-ray photoelectron spectroscopy, and pore-size distribution analysis. We believe that this simple approach is useful to improve alternative ORR electrocatalysts up to the level necessary for practical applications.

Functionalized graphene-based cathode for highly reversible lithium-sulfur batteries.

In this article, we highlight the salient issues in the development of lithium-sulfur battery (LSB) cathodes, present different points of view in solving them, and argue, why in the future, functionalized graphene or graphene oxide might be the ultimate solution towards LSB commercialization. As shown by previous studies and also in our recent work, functionalized graphene and graphene oxide enhance the reversibility of the charge-discharge process by trapping polysulfides in the oxygen functional groups on the graphene surface, thus minimizing polysulfide dissolution. This will be helpful for the rational design of new cathode structures based on graphene for LSBs with minimal capacity fading, low extra cost, and without the unnecessary weight increase caused by metal/metal oxide additives.

An etched nanoporous Ge anode in a novel metal-air energy conversion cell.

We first report the successful synthesis of porous germanium with ordered hierarchical structures, via controlled etching, and show its performance as an anode in a new metal-air battery. Our experimental results demonstrate the potential use of porous germanium in a high power density Ge-air energy conversion cell, showing a stable long-term discharge profile at various current drains.