Stabilization of High-Valent Molecular Cobalt Sites through Oxidized Phosphorus in Reduced Graphene Oxide for Enhanced Oxygen Evolution Catalysis.

Heterogeneous molecular cobalt (Co) sites represent one type of classical catalytic sites for electrochemical oxygen evolution reaction (OER) in alkaline solutions. There are dynamic equilibriums between Co2+, Co3+ and Co4+ states coupling with OH-/H+ interaction before and during the OER event. Since the emergence of Co2+ sites is detrimental to the OER cycle, the stabilization of high-valent Co sites to shift away from the equilibrium becomes critical and is proposed as a new strategy to enhance OER. Herein, phosphorus (P) atoms were doped into reduced graphene oxide to link molecular Co2+ acetylacetonate toward synthesizing a novel heterogeneous molecular catalyst. By increasing the oxidation states of P heteroatoms, the linked Co sites were spontaneously oxidized from 2+ to 3+ states in a KOH solution through OH- ions coupling at an open circuit condition. With excluding the Co2+ sites, the as-derived Co sites with 3+ initial states exhibited intrinsically high OER activity, validating the effectiveness of the strategy of stabilizing high valence Co sites.

PTFE as a Multifunctional Binder for High-Current-Density Oxygen Evolution.

Binder plays a crucial role in constructing high-performance electrodes for water electrolysis. While most research has been focused on advancing electrocatalysts, the application of binders in electrode design has yet to be fully explored. Herein, the in situ incorporation of polytetrafluoroethylene (PTFE) as a multifunctional binder, which increases electrochemical active sites, enhances mass transfer, and strengthens the mechanical and chemical robustness of oxygen evolution reaction (OER) electrodes, is reported. The NiFe-LDH@PTFE/NF electrode prepared by co-deposition of PTFE with NiFe-layered double hydroxide onto nickel foam demonstrates exceptional long-term stability with a minimal potential decay rate of 0.034 mV h-1 at 500 mA cm-2 for 1000 h. The alkaline water electrolyzer utilizing NiFe-LDH@PTFE/NF requires only 1.584 V at 500 mA cm-2 and sustains high energy efficiency over 1000 h under industrial operating conditions. This work opens a new path for stabilizing active sites to obtain durable electrodes for OER as well as other electrocatalytic systems.

Superhydrophilic and Underwater Superaerophobic Dual-Function Peony-Shaped Selenide Micro-nano Array Self-Supported Electrodes for High-Efficiency Overall Water Splitting Driven by Renewable Energy.

With the intensification of global environmental pollution and resource scarcity, hydrogen has garnered significant attention as an ideal alternative to fossil fuels due to its high energy density and nonpolluting nature. Consequently, the urgent development of electrocatalytic water-splitting electrodes for hydrogen production is imperative. In this study, a superwetting selenide catalytic electrode with a peony-flower-shaped micronano array (MoS2/Co0.8Fe0.2Se2/NixSey/nickel foam (NF)) was synthesized on NF via a two-step hydrothermal method. The optimal catalytic activity of cobalt-iron selenide was achieved by adjusting the Co/Fe ratio. The intrinsic catalytic activity of the electrodes was enhanced by incorporating transition metal selenides, which then served as a precursor for the subsequent loading of MoS2 nanoflowers on the surface to fully expose the active sites. Furthermore, the superwetting properties of the electrode accelerated electrolyte penetration and electron/mass transfer, while also facilitating bubble detachment from the electrode surface, thereby preventing "bubble shielding effect". This resulted in superior oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performance, as well as overall water splitting capabilities. In a 1.0 M KOH solution, the electrode required only 166 and 195 mV overpotential to achieve a current density of 10 mA cm-2 for OER and HER, respectively. When functioning as a bifunctional catalytic electrode, only 1.60 V of voltage was necessary to drive the electrolyzer to reach a current density of 10 mA cm-2. Moreover, laboratory simulations of wind and solar energy-driven water splitting validated the feasibility of establishing a sustainable energy-to-hydrogen production chain. This work provides new insights into the preparation of low-overpotential, high-catalytic-activity superhydrophilic and underwater superaerophobic catalytic electrodes by rationally adjusting elemental ratios and exploring changes in electrode surface wettability.

Iron and Nickel Substituted Perovskite Cobaltites for Sustainable Oxygen Evolving Anodes in Alkaline Environment.

Perovskite oxides have great flexibility in their elemental composition, which is accompanied by large adjustability in their electronic properties. Herein, we synthesized twelve perovskites oxide-based catalysts for the oxygen evolution reaction (OER) in alkaline media. The catalysts are based on the parent oxide perovskite Ba0.5Gd0.8La0.7Co2O6-δ (BGLC587) and are synthesized through the sol-gel citrate synthesis route. To reduce the demand on cobalt (Co), but also increase the intrinsic catalytic activity of BGLC587 for the OER, we substitute Co on the B-site with certain amounts of Fe and Ni, synthesizing catalysts of the general formula Ba0.5Gd0.8La0.7Co2-x-yFexNiyO6-δ. A plethora of physicochemical and electrochemical methods suggest that an Fe content between 30% and 70% increases the intrinsic catalytic activity of BGLC587, while Tafel slopes in combination with in-situ Raman spectroscopy suggest the rate determining step is likely a proton-exchange reaction, progressing possibly through the lattice oxygen mechanism (LOM). We apply one of the optimized, Co-substituted perovskites in a monolithic, photovoltaic (PV)-driven electrolysis cell and we achieve an initial solar-to-hydrogen (STH) conversion efficiency of 10.5% under one sun solar simulated illumination.

Poly(Arylene Alkylene)s with Tetrazole Pendants for Alkaline Ion-Solvating Polymer Electrolytes.

Alkaline ion-solvating membranes derived from a tetrazole functionalized poly(arylene alkylene) are prepared, characterized and evaluated as electrode separators in alkaline water electrolysis. The base polymer, poly[[1,1'-biphenyl]-4,4'-diyl(1,1,1-trifluoropropan-2-yl)], is synthesized by superacid catalyzed polyhydroxyalkylation and subsequently functionalized with tetrazole pendants. After equilibration in aqueous KOH, the relatively acidic tetrazole pendants are deprotonated to form the corresponding potassium tetrazolides. The room temperature ion conductivity is found to peak at 19 mS cm-1 in 5 wt. % KOH, and slightly declines with increasing KOH concentration to 13 mS cm-1 in 30 wt. % KOH. Based on an overall assessment of the mechanical properties, conductivity and electrode activity, 30 wt. % KOH is applied for alkaline electrolysis cell tests. Current densities of up to 1000 mA cm-2 were reached with uncatalyzed Ni-foam electrodes at a cell voltage of less than 2.6 V, with improved gas barrier characteristics compared to that of the several times thicker Zirfon separator.

Engineering Robust Triazine Crosslinked and Pyridine Capped Anion Exchange Membrane for Advanced Water Electrolysis.

Exploring high-performance anion exchange membranes (AEM) for water electrolyzers (AEMWEs) is significant for green hydrogen production. However, the current AEMWEs are restricted by the poor mechanical strength and low OH- conductivity of AEMs, leading to the low working stability and low current density. Here, we develop a robust AEM with polybiphenylpiperidium network by combining the crosslinking with triazine and the capping with pyridine for advanced AEMWEs. The AEM exhibits an excellent mechanical strength (79.4 MPa), low swelling ratio (19.2 %), persistent alkali stability (¼ 5,000 hours) and high OH- conductivity (247.2 mS cm-1) which achieves the state-of-the-art AEMs. Importantly, when applied in AEMWEs, the corresponding electrolyzer equipped with commercial nickel iron and nickel molybdenum catalysts obtained a current density of up to 3.0 A cm-2 at 2 V and could be stably operated ~430 h at a high current density of 1.6 A cm-2, which exceeds the most of AEMWEs. Our results suggest that triazine crosslinking and pyridine capping can effectively improve the overall performance of the AEMWEs.

Inhibiting Dissolution of Active Sites in 80 °C Alkaline Water Electrolysis by Oxyanion Engineering.

Commercial alkaline water electrolysers typically operate at 80 °C to minimize energy consumption. However, NiFe-based catalysts, considered as one of the most promising candidates for anode, encounter the bottleneck of high solubility at such temperatures. Herein, we discover that the dissolution of NiFe layered double hydroxides (NiFe-LDH) during operation not only leads to degradation of anode itself, but also deactivates cathode for water splitting, resulting in decay of overall electrocatalytic performance. Aiming to suppress the dissolution, we employed oxyanions as inhibitors in electrolyte. The added phosphates to the electrolyte inhibit the loss of NiFe-LDH active sites at 400 mA cm-2 to 1/3 of the original amount, thus reducing the rate of performance decay by 25-fold. Furthermore, the usage of borates, sulfates, and carbonates yields similar results, demonstrating the reliability and universality of the active site dissolution inhibitor, and its role in elevated water electrolysis.

Making waves: Power-to-X for the Water Resource Recovery Facilities of the future.

The wastewater industry and the energy system are undergoing significant transformations to address climate change and environmental pollution. Green hydrogen, which will be mainly obtained from renewable electricity water electrolysis (Power-to-Hydrogen, PtH), has been considered as an essential energy carrier to neutralize the fluctuations of renewable energy sources. PtH, or Power-to-X (PtX), has been allocated to multiple sectors, including industry, transport and power generation. However, considering its large potential for implementation in the wastewater sector, represented by Water Resource Recovery Facilities (WRRFs), the PtX concept has been largely overlooked in terms of planning and policymaking. This paper proposes a concept to implement PtX at WRRFs, where sourcing of water, utilization of the oxygen by-product, and PtX itself can be sustainable and diversified strategies. Potential value chains of PtX are presented and illustrated in the frame of a WWRF benchmark simulation model, highlighting the applications of oxygen from PtX through pure oxygen aeration and ozone disinfection. Opportunities and challenges are highlighted briefly, and so is the prospective outlook to the future. Ultimately, it is concluded that 'coupling PtX to WRRFs' is a promising solution, which will potentially bring sustainable opportunities for both WRRFs and the energy system. Apart from regulatory and economic challenges, the limitations in coupling PtX to WRRFs mainly come from energy efficiency concerns and the complexity of the integration of the water framework and the energy system.

Comparison of life cycle assessment between hydrogen production from silicon waste and alkaline water electrolysis.

With global warming becoming increasingly severe, environmental issues are receiving international attention. Crystalline silicon is an indispensable and important raw material for photovoltaic and semiconductor fields, but the cutting of crystalline silicon materials generates a large amount of silicon wastes. This article evaluates the environmental impact of a hydrogen production process using diamond-wire sawing silicon waste (DSSW) using the life cycle assessment (LCA) methodology. For comparison, it was also analyzed the environmental impact of the alkaline water electrolysis (AEL) hydrogen production route. In the DSSW alkaline catalyzed hydrolysis (DACH) hydrogen production route, the hydrogen production stage accounts for the main contribution of nine environmental impact indexes, including GWP, PED, ADP, AP, EP, ODP, ET, HT-cancer, and HT-non cancer, exceeding 56 %. Whereas for the AEL route, the environmental impacts of the electrolytic cell manufacturing stage can be neglected, and the operating stage contributes almost all the environmental impacts, contributing more than 92 % to the twelve environmental impact indexes. Compared to the AEL route, the DACH route has higher environmental impacts, with GWP index reaching 87.78 kg CO2 -eq/kg H2, PED index reaching 1772.90 MJ/kg H2, and IWU index reaching 622.37 kg/kg H2 which are 2.85, 4.07 and 7.56 times higher than the former, respectively. Although the environmental impact of the DACH route is significant, most of its indirect impacts were caused by the use of raw materials, and the energy consumption and direct environmental impact are both low. The environmental impact of the AEL route is mainly indirect effects generated due to the use of electricity. If clean renewable energy sources (e.g., solar PV, hydropower, geothermal or biofuels), were used for the AEL route, all twelve environmental impact indexes would be significantly reduced.

Hydrophilic Chitosan-Doped Composite Diaphragm Reducing Gas Permeation for Alkaline Water Electrolysis Producing Hydrogen.

The present paper studied the chitosan-doped composite diaphragm by the phase exchange method with the objective of developing a composite diaphragm that complies with the alkaline water electrolysis requirements, as well as tested the electrolytic performance of the diaphragm in alkaline water electrolysis. The structure and morphology are characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The performance of chitosan-doped composite diaphragms was tested; CS3Z12 composite diaphragm with a low area resistance (0.20 Ω cm2), a high bubble point pressure (2.75 bar), and excellent electrochemical performance (current density of 650 mA cm-2 at 1.83 V) shows the best performance. Moreover, the performance of the synthesized composite diaphragm is significantly elevated compared to commercial diaphragms (Zirfon PERL), which is promising for practical application in alkaline electrolytic cells.

Single Atom Iridium Decorated Nickel Alloys Supported on Segregated MoO2 for Alkaline Water Electrolysis.

Hetero-interface engineering has been widely employed to develop supported multicomponent catalysts for water electrolysis, but it still remains a substantial challenge for supported single atom alloys. Herein a conductive oxide MoO2 supported Ir1 Ni single atom alloys (Ir1 Ni@MoO2 SAAs) bifunctional electrocatalysts through surface segregation coupled with galvanic replacement reaction, where the Ir atoms are atomically anchored onto the surface of Ni nanoclusters via the Ir-Ni coordination accompanied with electron transfer from Ni to Ir is reported. Benefiting from the unique structure, the Ir1 Ni@MoO2 SAAs not only exhibit low overpotential of 48.6 mV at 10 mA cm-2 and Tafel slope of 19 mV dec-1 for hydrogen evolution reaction, but also show highly efficient alkaline water oxidation with overpotential of 280 mV at 10 mA cm-2 . Their overall water electrolysis exhibits a low cell voltage of 1.52 V at 10 mA cm-2 and excellent durability. Experiments and theoretical calculations reveal that the Ir-Ni interface effectively weakens hydrogen binding energy, and decoration of the Ir single atoms boost surface reconstruction of Ni species to enhance the coverage of intermediates (OH*) and switch the potential-determining step. It is suggested that this approach opens up a promising avenue to design efficient and durable precious metal bifunctional electrocatalysts.

Surface-Modified Carbon Nanotubes with Ultrathin Co3O4 Layer for Enhanced Oxygen Evolution Reaction.

Alkaline water electrolysis is a vital technology for sustainable and efficient hydrogen production. However, the oxygen evolution reaction (OER) at the anode suffers from sluggish kinetics, requiring overpotential. Precious metal-based electrocatalysts are commonly used but face limitations in cost and availability. Carbon nanostructures, such as carbon nanotubes (CNTs), offer promising alternatives due to their abundant active sites and efficient charge-transfer properties. Surface modification of CNTs through techniques such as pulsed laser ablation in liquid media (PLAL) can enhance their catalytic performance. In this study, we investigate the role of surface-modified carbon (SMC) as a support to increase the active sites of transition metal-based electrocatalysts and its impact on electrocatalytic performance for the OER. We focus on Co3O4@SMC heterostructures, where an ultrathin layer of Co3O4 is deposited onto SMCs using a combination of PLAL and atomic layer deposition. A comparative analysis with aggregated Co3O4 and Co3O4@pristine CNTs reveals the superior OER performance of Co3O4@SMC. The optimized Co3O4@SMC exhibits a 25.6% reduction in overpotential, a lower Tafel slope, and a significantly higher turnover frequency (TOF) in alkaline water splitting. The experimental results, combined with density functional theory (DFT) calculations, indicate that these improvements can be attributed to the high electrocatalytic activity of Co3O4 as active sites achieved through the homogeneous distribution on SMCs. The experimental methodology, morphology, composition, and their correlation with activity and stability of Co3O4@SMC for the OER in alkaline media are discussed in detail. This study contributes to the understanding of SMC-based heterostructures and their potential for enhancing electrocatalytic performance in alkaline water electrolysis.

Effect of carbon support on the activity of monodisperse Co45Pt55 nanoparticles for oxygen evolution in alkaline media.

Oxygen evolution reaction (OER) represents the efficiency-limiting reaction in water electrolyzers, metal-air batteries, and unitized regenerative fuel cells. To achieve high-efficiency OER in alkaline media, we fabricated three novel electrocatalysts by the assembly of as-prepared Co45Pt55 alloy nanoparticles (NPs) on three different carbon-based support materials: reduced graphene oxide (CoPt/rGO), mesoporous graphitic carbon nitride (CoPt/mpg-CN), and commercial Ketjenblack carbon (CoPt/KB). Voltammetry studies revealed that CoPt/rGO electrocatalyst provided lower OER overpotentials accompanied by higher currents and specific current density values than the other two studied materials. Moreover, CoPt/rGO outperformed commercial CoPt/C electrocatalysts in terms of notably higher specific current densities. Additionally, it was found that CoPt/rGO electrocatalyst activity increases with increasing temperature up to 85°C, as suggested by the increase in the exchange current density. Electrochemical impedance spectroscopy studies of three electrocatalysts in OER revealed similar charge transfer resistance, although CoPt/rGO provided a higher current density. The main issue observed during long-term chronoamperometry and chronopotentiometry studies is the materials' instability under OER polarization conditions, which is still to be tackled in future work.

Multilayered NiMo/CoMn/Ni Cathodic Electrodes with Enhanced Activity and Stability toward Alkaline Water Electrolysis.

In this study, multilayered NiMo/CoMn/Ni cathodic electrodes were prepared by the multilayered electrodeposition method. The multilayered structure includes a nickel screen substrate, CoMn nanoparticles at the bottom, and cauliflower-like NiMo nanoparticles at the top. The multilayered electrodes have a lower overpotential, preferable stability, and better electrocatalytic performance than monolayer electrodes. In a three-electrode system, the overpotentials of the multilayered NiMo/CoMn/Ni cathodic electrodes at 10 and 500 mA/cm2 are only 28.7 and 259.1 mV, respectively. The overpotential rise rate of the electrodes after constant current tests at 200 and 500 mA/cm2 was 4.42 and 8.74 mV/h, respectively, and the overpotential rise rate after 1000 cycles of cyclic voltammetry of the electrodes was 1.9 mV/h, while the overpotential rise rate after the three stability tests of the nickel screen was 5.49, 11.42, and 5.1 mV/h. According to the Tafel extrapolation polarization curve, the Ecorr and Icorr of the electrodes were -0.3267 V and 1.954 × 10-5 A/cm2, respectively. The charge transfer rate of the electrodes is slightly slower than that of the monolayer electrodes, indicating that its corrosion resistance is more excellent. An electrolytic cell was designed for the overall water-splitting test, and the current density of the electrodes was 121.6 mA/cm2 at 1.8 V. In addition, the stability of the electrodes is excellent after intermittent testing for 50 h, which can greatly reduce power consumption and is more suitable for industrial overall water-splitting tests. In addition, the three-dimensional model was used to simulate the three-electrode system and alkaline water electrolytic cell system, and the simulation results are consistent with the experimental results. The hydrogen adsorption free energy (ΔGH) of the electrodes was -1.0191 eV, which was evaluated by density functional theory (DFT). The ΔGH is closer to zero than that of the monolayer electrodes, indicating that the surface has stronger adsorption of hydrogen atoms.

Thin Film Composite Membranes as a New Category of Alkaline Water Electrolysis Membranes.

Alkaline water electrolysis (AWE) is considered a promising technology for green hydrogen (H2 ) production. Conventional diaphragm-type porous membranes have a high risk of explosion owing to their high gas crossover, while nonporous anion exchange membranes lack mechanical and thermochemical stability, limiting their practical application. Herein, a thin film composite (TFC) membrane is proposed as a new category of AWE membranes. The TFC membrane consists of an ultrathin quaternary ammonium (QA) selective layer formed via Menshutkin reaction-based interfacial polymerization on a porous polyethylene (PE) support. The dense, alkaline-stable, and highly anion-conductive QA layer prevents gas crossover while promoting anion transport. The PE support reinforces the mechanical and thermochemical properties, while its highly porous and thin structure reduces mass transport resistance across the TFC membrane. Consequently, the TFC membrane exhibits unprecedentedly high AWE performance (1.16 A cm-2 at 1.8 V) using nonprecious group metal electrodes with a potassium hydroxide (25 wt%) aqueous solution at 80 °C, significantly outperforming commercial and other lab-made AWE membranes. Moreover, the TFC membrane demonstrates remarkably low gas crossover, long-term stability, and stack cell operability, thereby ensuring its commercial viability for green H2 production. This strategy provides an advanced material platform for energy and environmental applications.

Facile formation of Zn-incorporated NiFe layered double hydroxide as highly-efficient oxygen evolution catalyst.

Electrochemical water splitting is the primary method to produce green hydrogen, which is considered an efficient alternative to fossil fuels for achieving carbon neutrality. For meeting the increasing market demand for green hydrogen, high-efficiency, low-cost, and large-scale electrocatalysts are crucial. In this study, we report a simple spontaneous corrosion and cyclic voltammetry (CV) activation method to fabricate Zn-incorporated NiFe layered double hydroxide (LDH) on commercial NiFe foam, which shows excellent oxygen evolution reaction (OER) performance. The electrocatalyst achieves an overpotential of 565 mV and outstanding stability of up to 112 h at 400 mA cm-2. The active layer for OER is shown to be ß-NiFeOOH according to the results of in-situ Raman. Our findings suggest that the NiFe foam treated by simple spontaneous corrosion has promising industrial applications as a highly efficient OER catalyst.

Ni electrodes with 3D-ordered surface structures for boosting bubble releasing toward high current density alkaline water splitting.

The performance of alkaline water electrolysis (AWE) at high current densities is limited by gas bubble generation on the surface of electrodes, which covers active sites and blocks mass transfer, resulting in lower AWE efficiency. Here, we utilize electro-etching to construct Ni electrodes with hydrophilic and aerophobic surfaces to improve the efficiency of AWE. Ni atoms on the Ni surface can be exfoliated orderly along the crystal planes by electro-etching, forming micro-nano-scale rough surfaces with multiple crystal planes exposed. The 3D-ordered surface structures increase the exposure of active sites and promote the removal of bubbles on the surface of the electrode during the AWE process. In addition, experimental results from high-speed camera reveal that rapidly released bubbles can improve the local circulation of electrolyte. Lastly, the accelerated durability test based on practical working condition demonstrates that the 3D-ordered surface structures are robust and durable during the AWE process.

Suppression of Catalyst Layer Detachment by Interfacial Microstructural Modulation of the NiCo2O4/Ni Oxygen Evolution Electrode for Renewable Energy-Powered Alkaline Water Electrolysis.

Alkaline water electrolysis (AWE) is a large-scale hydrogen production technology. A major degradation mode of AWE when using fluctuating power derived from renewable energies is the detachment of the catalyst layer (CL). Here, this study investigates the CL detachment mechanism of NiCo2O4-CL-coated Ni (NCO/Ni) electrodes under an accelerated durability test (ADT) simulating a fluctuating power and the effect of post-annealing on detachment behavior. Microstructural analysis reveals that detachment begins at the nanoscale gaps between the stacked CLs and between CL and the substrate. Post-annealing at 400 °C removes the degradation starting point in CL, and a composition gradient Co-doped NiO interlayer and NiO(111)/Ni(111) epitaxial interface form between CL and the Ni substrate, nearly suppressing CL detachment. Although the electrode performance of the annealed sample is initially lower than that of the as-prepared sample, the overpotential is significantly reduced during ADT due to the formation of the NiCo hydroxide active surface layer. These results demonstrate that interfacial microstructural modulation by post-annealing is a powerful approach to realizing durable electrodes for green hydrogen production by renewable energy-powered AWE.

Electrocatalytic Properties of Co3O4 Prepared on Carbon Fibers by Thermal Metal-Organic Deposition for the Oxygen Evolution Reaction in Alkaline Water Electrolysis.

Cobalt oxide (Co3O4) serves as a promising electrocatalyst for oxygen evolution reactions (OER) in water-electrolytic hydrogen production. For more practical applications, advances in dry-deposition processes for the high-throughput fabrication of such Co3O4 electrocatalysts are needed. In this work, a thermal metal-organic deposition (MOD) technique is developed to form Co3O4 deposits on microscale-diameter carbon fibers constituting a carbon fiber paper (CFP) substrate for high-efficiency OER electrocatalyst applications. The Co3O4 electrocatalysts are deposited while uniformly covering the surface of individual carbon fibers in the reaction temperature range from 400 to 800 °C under an ambient Ar atmosphere. It is found that the microstructure of deposits is dependent on the reaction temperature. The Co3O4 electrocatalysts prepared at 500 °C and over exhibit values of 355-384 mV in overpotential (η10) required to reach a current density of 10 mA cm-2 and 70-79 mV dec-1 in Tafel slope, measured in 1 M KOH aqueous solution. As a result, it is highlighted that the improved crystallinity of the Co3O4 electrocatalyst with the increased reaction temperature leads to an enhancement in electrode-level OER activity with the high electrochemically active surface area (ECSA), low charge transfer resistance (Rct), and low η10, due to the enhanced electrical conductivity. On the other hand, it is found that the inherent catalytic activity of the surface sites of the Co3O4, represented by the turnover frequency (TOF), decreases with reaction temperature due to the high-temperature sintering effect. This work provides the groundwork for the high-throughput fabrication and rational design of high-performance electrocatalysts.

Hydroxyapatite-Derived Heterogeneous Ru-Ru2 P Electrocatalyst and Environmentally-Friendly Membrane Electrode toward Efficient Alkaline Electrolyzer.

Alkaline membrane water electrolysis is a promising production technology, and advanced electrocatalyst and membrane electrode design have always been the core technology. Herein, an ion-exchange method and an environmentally friendly in situ green phosphating strategy are successively employed to fabricate Ru-Ru2 P heterogeneous nanoparticles by using hydroxyapatite (HAP) as a phosphorus source, which is an exceptionally active electrocatalyst for hydrogen evolution reaction (HER). Density functional theory calculation results reveal that strong electronic redistribution occurs at the heterointerface of Ru-Ru2 P, which modulates the electronic structure to achieve an optimized hydrogen adsorption strength. The obtained Ru-Ru2 P possesses excellent HER performance (24 mV at 10 mA cm-2 ) and robust stability (1000 mA cm-2 for 120 h) in alkaline media. Furthermore, an environmentally friendly membrane electrode with a sandwich structure is assembled by HAP nanowires as an alkaline membrane, Ru-Ru2 P as a cathodic catalyst, and NiFe-LDH as an anodic catalyst, respectively. The voltage of (-) Ru-Ru2 P || NiFe-LDH/CNTs (+) (1.53 V at 10 mA cm-2 ) is lower than that of (-) 20 wt% Pt/C || RuO2 (+) (1.60 V at 10 mA cm-2 ) for overall water splitting. Overall, the studies not only design an efficient catalyst but also provide a new route to achieve a high-stability electrolyzer for industrial H2 production.