Construction of Defect-Rich Ni-Fe-Doped K0.23 MnO2 Cubic Nanoflowers via Etching Prussian Blue Analogue for Efficient Overall Water Splitting

Molybdenum oxide/nickel molybdenum oxide heterostructures hybridized active platinum co-catalyst toward superb-efficiency water splitting catalysis

A new catalyst has been developed that utilizes molybdenum oxide (MoO3)/nickel molybdenum oxide (NiMoO4) heterostructured nanorods coupled with Pt ultrafine nanoparticles for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) toward industrial-grade water splitting. This catalyst has been synthesized using a versatile approach and has shown to perform better than noble-metals catalysts, such as Pt/C and RuO2, at industrial-grade current level (≥1000 mA·cm-2). When used simultaneously as a cathode and anode, the proposed material yields 10 mA·cm-2 at a remarkably small cell voltage of 1.55 V and has shown extraordinary durability for over 50 h. Density functional theory (DFT) calculations have proved that the combination of MoO3 and NiMoO4 creates a metallic heterostructure with outstanding charge transfer ability. The DFT calculations have also shown that the excellent chemical coupling effect between the MoO3/NiMoO4 and Pt synergistically optimize the charge transfer capability and Gibbs free energies of intermediate species, leading to remarkably speeding up the reaction kinetics of water electrolysis.

Phase-Induced Strain Effect to Synthesize an Iron-Doped Orthogonal Cobalt Selenide Electrocatalyst for the Oxygen Evolution Reaction

The etching effect has the capability to control atom doping and trigger phase transformation, thereby enhancing the electrocatalytic reaction. Herein, iron-doped cobalt selenide (Fe-CoSe2) nanoparticle-decorated carbon nanofibers (Fe-CoSe2/CNFs) are synthesized by assembling an FeCo-Prussian blue analogue (FeCo-PBA) cube precursor with polyacrylonitrile fibers and then treating with hydrochloric acid, followed by gas phase selenization. The Fe-CoSe2/CNFs catalyst exhibits a large surface area and a porous structure, facilitating the permeation of electrolytes. Moreover, orthorhombic CoSe2 is obtained, which is in favor of improving the oxygen evolution reaction (OER). By modulating the etching time, the ideal crystal phase and the optimal amount of the dopant (Fe) can be achieved, thus showing favorable OER activity. Specifically, the Fe-CoSe2/CNFs electrocatalyst enables high electrocatalytic activity for the OER with a low overpotential of 263 mV to drive a current density of 10 mA cm-2 in 1 M KOH. A small Tafel slope of 51 mV dec-1 shows fast charge transfer kinetics. Density functional theory (DFT) calculations reveal that Fe-doped orthorhombic CoSe2(111) can modulate the electron structure, contributing to OH- adsorption ability. Given this, a strategy for phase transformation induced by etching technology is proposed to improve the intrinsic activity of the catalyst.

Synergy of Interface Coupling and Sulfur Vacancies in Ni3S2/Fe2P for Water Splitting

Integrated application of interface engineering and vacancy engineering is a promising and effective strategy for the design and fabrication of high-performance electrocatalysts. Herein, the heterointerface catalyst with rich sulfur vacancies, vs-Ni3S2/Fe2P, was successfully designed and constructed. The strong heterointerface coupling and rich sulfur vacancies in vs-Ni3S2/Fe2P significantly optimize the electronic structure of the catalyst and synergistically improve the inherent catalytic activity. Benefiting from the optimization of the electronic structure, vs-Ni3S2/Fe2P exhibits excellent bifunctional electrocatalytic performance in alkaline electrolytes. The overpotentials for hydrogen and oxygen evolution reactions (HER and OER) are 99 and 169 mV at a current density of 10 mA cm-2, respectively. Particularly, it achieves an ultrahigh OER performance with an overpotential of 251 mV at 300 mA cm-2. Moreover, the catalyst also displays outstanding long-term durability. Density functional theory (DFT) computations reveal that the synergy of interface coupling and sulfur vacancies is crucial to optimizing the electronic structure. This study offers a hopeful pathway for the design and construction of durable and efficient electrocatalysts.

Suppressing Jahn-Teller distortion and locking lattice water with doped Fe(III) in birnessite toward fast and stable zinc-ion batteries

Birnessite has been regarded as a promising cathode material for aqueous zinc-ion batteries (ZIBs), but severe Jahn-Teller distortion and abrupt lattice collapse at deep charged states lead to serious problems such as poor capacity retention and short cycle life, which severely impede its practical applications. We herein report the construction of an advanced layered Fe-doped Na0.55Mn2O4·xH2O (Fe-NMO·xH2O) cathode to promote zinc-ion storage performance and electrochemical stability. An outstanding capacity of 102 mA h g-1 at a high current density of 20 A g-1 and a long cycle life of 6000 cycles have been achieved, comparable to the state-of-the-art manganese oxide-based cathodes. Both experimental measurements and theoretical calculations reveal that Fe3+ substitution and lattice water cooperatively stabilize the interlayer structure, accelerate zinc-ion diffusion, and improve electronic conductivity. Notably, Fe doping is conducive to alleviating the Jahn-Teller effect and locking lattice water, which effectively prevents phase transformation and lattice collapse during the (de)intercalation process. This work sheds light on the synergistic interplay between dopants and structural water in zinc-ion storage and demonstrates instructive strategies to regulate layered structures for ZIBs.

Facile fabrication of Ni, Fe-doped δ-MnO2 derived from Prussian blue analogues as an efficient catalyst for stable Li-CO2 batteries

Rechargeable Li-CO2 batteries are regarded as an ideal new-generation energy storage system, owing to their high energy density and extraordinary CO2 capture capability. Developing a suitable cathode to improve the electrochemical performance of Li-CO2 batteries has always been a research hotspot. Herein, Ni-Fe-δ-MnO2 nano-flower composites are designed and synthesized by in situ etching a Ni-Fe PBA precursor as the cathode for Li-CO2 batteries. Ni-Fe-δ-MnO2 nanoflowers composed of ultra-thin nanosheets possess considerable surface spaces, which can not only provide abundant catalytic active sites, but also facilitate the nucleation of discharge products and promote the CO2 reduction reaction. On the one hand, the introduction of Ni and Fe elements can improve the electrical conductivity of δ-MnO2. On the other hand, the synergistic catalytic effect between Ni, Fe elements and δ-MnO2 will greatly enhance the cycling performance and reduce the overpotential of Li-CO2 batteries. Consequently, the Li-CO2 battery based on the Ni-Fe-δ-MnO2 cathode shows a high discharge capacity of 8287 mA h g-1 and can stabilize over 100 cycles at a current density of 100 mA g-1. The work offers a promising guideline to design efficient manganese-based catalysts for Li-CO2 batteries.

Metal nitrides for seawater electrolysis

Electrocatalytic high-throughput seawater electrolysis for hydrogen production is a promising green energy technology that offers possibilities for environmental and energy sustainability. However, large-scale application is limited by the complex composition of seawater, high concentration of Cl- leading to competing reaction, and severe corrosion of electrode materials. In recent years, extensive research has been conducted to address these challenges. Metal nitrides (MNs) with excellent chemical stability and catalytic properties have emerged as ideal electrocatalyst candidates. This review presents the electrode reactions and basic parameters of the seawater splitting process, and summarizes the types and selection principles of conductive substrates with critical analysis of the design principles for seawater electrocatalysts. The focus is on discussing the properties, synthesis, and design strategies of MN-based electrocatalysts. Finally, we provide an outlook for the future development of MNs in the high-throughput seawater electrolysis field and highlight key issues that require further research and optimization.

Coupling effect and electronic modulation for synergistically enhanced overall alkaline water splitting on bifunctional Fe-doped CoBi/CoP nanoneedle arrays

Designing bifunctional electrocatalysts with high efficiency and low cost for water splitting is urgently required for the production of green hydrogen. Herein, a bifunctional iron-doped cobalt borate/cobalt phosphide hybrid supported on nickel foam (Fe-CoBi/CoP/NF) was fabricated via hydrothermal and phosphating process. Benefit from the unique nanoneedle architecture for faster mass transfer, the existence of borate on CoBi for accelerating proton transfer, the moderate adsorption of H* species on CoP, Fe doping and the synergistic effect between CoBi and CoP, Fe-CoBi/CoP/NF hybrid exhibits a low overpotential of 137 mV and 260 mV at 100 mA cm-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Moreover, Fe-CoBi/CoP/NF||Fe-CoBi/CoP/NF also presents a low cell potential of 1.65 V@100 mA cm-2 for overall alkaline water splitting and excellent durability (128 h) without decay. This work provides a new insight into the design of bifunctional electrocatalysts simultaneously through the morphological engineering and heteroatomic doping.

Cation-doped sea-urchin-like MnO2 for electrocatalytic overall water splitting

It is necessary to take full account of the activity, selectivity, dynamic performance, economic benefits, and environmental impact of the catalysts in the overall water splitting of electrocatalysis for the reasonable design of electrocatalysts. Designing nanostructures of catalysts and optimizing defect engineering are considered environmentally friendly and cost-effective electrocatalyst synthesis strategies. Herein, we report that metal cations regulate the microstructure of sea-urchin-like MnO2 and act as dopants to cause the lattice expansion of MnO2, resulting in crystal surface defects. The valence unsaturated Mn4+/Mn3+ greatly promotes the electrocatalytic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The optimal Al-MnO2 showed that the overpotential is 390 and 170 mV in the process of catalyzing OER and HER, respectively, at a current density of 10 mA cm-2. It is exciting to note that after 5000 cycles of Al-MnO2 within the kinetic potential range of OER and HER, its performance remained almost unchanged. This work provides a simple, efficient, and environmentally friendly route for the design of efficient integrated water-splitting electrocatalysts.

Modulating Electronic Structure of PtCo-Ptrich Nanowires with Ru atoms for Boosted Hydrogen Evolution Catalysis

Rational design and development of highly efficient hydrogen evolution reaction (HER) electrocatalysts is of great significance for the development of green water electrolysis hydrogen production technology. Ru-engineered 1D PtCo-Ptrich nanowires (Ru-Ptrich Co NWs) are fabricated by a facile electrodeposition method. The rich Pt surface on 1D Pt3 Co contributes to the fully exposed active sites and enhanced intrinsic catalytic activity (co-engineered by Ru and Co atoms) for HER. The incorporation of Ru atoms can not only accelerate the water dissociation in alkaline condition to provide sufficient H* but also modulate the electronic structure of Pt to achieve optimized H* adsorption energy. As a result, Ru-Ptrich Co NWs have exhibited ultralow HER overpotentials (η) of 8 and 112 mV to achieve current densities of 10 and 100 mA cm-2 in 1 m KOH, respectively, which far exceed those of commercial Pt/C catalyst (η10  = 29 mV, η100  = 206 mV). Density functional theory (DFT) calculations further demonstrate that the incorporated Ru atoms possess strong water adsorption capacity (-0.52 vs -0.12 eV for Pt), facilitating water dissociation. The Pt atoms in the outermost Pt-rich skin of Ru-Ptrich Co NWs achieve optimized H* adsorption free energy (ΔGH* ) of -0.08 eV, boosting hydrogen generation.

Structure and oxygen vacancy engineered CuCo-layered double oxide nanotube arrays as advanced bifunctional electrocatalysts for overall water splitting

In recent years, as a green renewable energy production technology, electrochemical water splitting has demonstrated high development potential. Many materials have been reported as successful catalysts in the water-splitting field. However, it is still a huge challenge to produce bifunctional electrocatalysts for the efficient and sustainable generation of hydrogen and oxygen simultaneously. Herein, we successfully developed oxygen vacancies abundant CuCo layered double oxide (O_v-CuCo-LDO) hollow nanotube arrays (HNTAs) loaded on nickel foam as advanced electrocatalysts for total water splitting. When the current density was 10 mA cm^-2, the O_v-CuCo-LDO HNTAs exhibited outstanding onset overpotentials of 53.9 and 72.5 mV for the hydrogen evolution and oxygen evolution reactions (HER and OER) in alkaline medium, respectively, because of the bimetallic synergistic effect between the cobalt and copper and the unique hollow porous structure. In addition, an as-assembled O_v-CuCo-LDO||O_v-CuCo-LDO electrolytic cell showed a small potential of 1.55 V to deliver a current density of 10 mA cm^-2. Moreover, it also showed remarkable durability after long-term overall water splitting for more than 20 h. The research results in this paper are of great interest to practical applications of the water decomposition process, providing clear and in-depth insights into preliminary robust and efficient multifunctional electrocatalysts for overall water splitting.

In situ growth of Prussian blue analogue-derived Fe-doped NiS on Ni(OH)2 for efficient hydrogen evolution reaction

The energy industry is placing more and more emphasis on the need for effective and affordable electrocatalysts for hydrogen evolution reactions (HER). In this work, an iron-doped NiS/Ni(OH)₂/CC composite material was synthesized by simple hydrothermal sulfurization processes of bimetallic Prussian blue analogue (PBAs) precursors grown in situ on three-dimensional (3D) Ni(OH)₂ nanosheets. The overpotential can be 103 mV to attain current densities of 10 mA cm^-2. The excellent catalytic activity of Fe-NiS/Ni(OH)₂/CC is because of the unique 3D structure and the uniform doping of iron caused by the in situ growth of PBA, as well as the high conductivity of the self-supported electrode carbon cloth.

Fabrication of manganese borate/iron carbide encapsulated in nitrogen and boron co-doped carbon nanowires as the accelerated alkaline full water splitting bi-functional electrocatalysts

With high prices of precious metals (such as platinum, iridium, and ruthenium) and transition metals (such as cobalt and nickel), the design of high-efficiency and low-cost non-precious-metal-based catalysts using iron (Fe) and manganese (Mn) metals for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are critical for commercial applications of water splitting devices. In the study, without using any template or surfactant, we successfully designed novel cross-linked manganese borate (Mn3(BO3)2) and iron carbide (Fe3C) embedded into boron (B) and nitrogen (N) co-doped three-dimensional (3D) hierarchically meso/macroporous carbon nanowires (denoted as FexMny@BN-PCFs). Electrochemical test results showed that the HER and OER catalytic activities of Fe1Mn1@BN-PCFs were close to those of 20 wt% Pt/C and RuO2. For full water splitting, (-) Fe1Mn1@BN-PCFs||Fe1Mn1@BN-PCF (+) cell achieved a current density of 10 mA cm-2 at a cell voltage of 1.622 V, which was 14.2 mV larger than that of (-) 20 wt% Pt/C||RuO2 (+) benchmark. The synergistic effect of 3D hierarchically meso/macroporous architectures, excellent charge transport capacity, and abundant active centers (cross-linked Mn3(BO3)2/Fe3C@BNC, BC3, pyridinic-N, MNC, and graphitic-N) enhanced the water splitting catalytic activity of Fe1Mn1@BN-PCFs. The (-) Fe1Mn1@BN-PCFs||Fe1Mn1@BN-PCF (+) cell exhibited excellent stability owing to the superior structural and chemical stabilities of 3D hierarchically porous Fe1Mn1@BN-PCFs.

Enhanced Electrochemical Water Oxidation Activity by Structural Engineered Prussian Blue Analogue/rGO Heterostructure

Prussian blue analogue (PBA), with a three-dimensional open skeleton and abundant unsaturated surface coordination atoms, attracts extensive research interest in electrochemical energy-related fields due to facile preparation, low cost, and adjustable components. However, it remains a challenge to directly employ PBA as an electrocatalyst for water splitting owing to their poor charge transport ability and electrochemical stability. Herein, the PBA/rGO heterostructure is constructed based on structural engineering. Graphene not only improves the charge transfer efficiency of the compound material but also provides confined growth sites for PBA. Furthermore, the charge transfer interaction between the heterostructure interfaces facilitates the electrocatalytic oxygen evolution reaction of the composite, which is confirmed by the results of the electrochemical measurements. The overpotential of the PBA/rGO material is only 331.5 mV at a current density of 30 mA cm⁻² in 1.0 M KOH electrolyte with a small Tafel slope of 57.9 mV dec⁻¹, and the compound material exhibits high durability lasting for 40 h.

Active Sites In Situ Implanted Hybrid Zeolitic Imidazolate Frameworks for a Water Oxidation Catalyst

Metal-organic frameworks (MOFs) have been a focus of research because of their unique porous structure, but they are usually not directly for electrocatalysis. Herein, we prepared a special class of Fe/Zn/Mo-based trimetallic hybrid zeolitic imidazolate frameworks by in situ solvothermal synthesis that have the potential to act directly as highly efficient oxygen evolution reaction electrocatalysts. This work provides a foundation for the preparation of multimetal MOFs and expands the investigation of electrocatalysts.

Multistep Sulfur Leaching for the Development of a Highly Efficient and Stable NiSx/Ni(OH)2/NiOOH Electrocatalyst for Anion Exchange Membrane Water Electrolysis

Nickel (poly)sulfides have been widely studied as anodic catalysts for alkaline water electrolysis owing to their diverse morphologies, high catalytic activities in the oxygen evolution reaction (OER), and low cost. To utilize low-cost and high-efficiency polysulfides with industry-relevant cycling stability, we develop a Ni-rich NiS_x/Ni(OH)₂/NiOOH catalyst derived from NiS₂/Ni₃S₄ nanocubes. Ni-rich NiS_x/Ni(OH)₂/NiOOH shows improved OER catalytic activity (η = 374 mV@50 mA cm^-2) and stability (0.1% voltage increase) after 65 h of a galvanostatic test at 10 mA cm^-2 compared with commercial Ni/NiO and hydrothermally synthesized Ni(OH)₂ (both show η > 460 mV@50 mA cm^-2 along with 4.40 and 1.92% voltage increase, respectively). A water-splitting electrolyzer based on Pt/C||AF1-HNN8-50||NiS_x/Ni(OH)₂/NiOOH exhibits a current density of 1800 mA cm^-2 at 2.0 V and 500 h high-rate stability at 1000 mA cm^-2 with negligible attenuation of only 0.12 mV h^-1. This work provides an understanding of truly stable species, intrinsic active phases of Ni polysulfides, their high-rate stability in a real cell, and sheds light on the development of stable chalcogenide-based anodic electrocatalysts for anion exchange membrane water electrolysis (AEMWE).

Construction of Petal-Like Ag NWs@NiCoP with Three-Dimensional Core-Shell Structure for Overall Water Splitting

High-efficiency, good electrical conductivity and excellent performance electrocatalysts are attracting growing attention in the field of overall water splitting. In order to achieve the desirable qualities, rational construction of the structure and chemical composition of electrocatalysts is of fundamental importance. Herein, petal-like structure Ni0.33Co0.67P shells grown on conductive silver nanowires (Ag NWs) cores as bifunctional electrocatalysts for overall water splitting were synthesized through a facile hydrothermal method and phosphorization. The resultant three-dimensional core-shell petal-like structure Ag NWs@Ni0.33Co0.67P possesses excellent catalytic activities in alkaline conditions with the overpotential of 259 mV for the oxygen evolution reaction (OER), 121 mV for the hydrogen evolution reaction (HER) and a full cell voltage of 1.64 V to reach the current density of 10 mA cm-2. Highly conductive Ag NWs as cores and high surface area petal-like Ni0.33Co0.67P as shells can endow outstanding catalytic performance for the bifunctional electrocatalyst. Thus, the synthetic strategy of the three-dimensional core-shell structure Ag NWs@Ni0.33Co0.67P considerably advances the practice of Ag NWs toward electrocatalysts.

Morphological modulation of iron carbide embedded nitrogen-doped hierarchically porous carbon by manganese doping as highly efficient bifunctional electrocatalysts for overall water splitting

In the development of water splitting, the sluggish electrocatalytic kinetics of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have restricted their energy conversion efficiencies. Along with the continuous rise in the prices of noble metals and transition metals (such as cobalt and nickel), constructing high-efficiency HER/OER catalysts based on low cost transition metals, such as iron and manganese, is becoming more meaningful in developing industrialized water splitting devices. In this paper, in the absence of a template or active agent, three-dimensional, hierarchically porous Fe_xMn_y nanoparticles (NPs) were embedded and nitrogen-doped carbon materials (denoted as Fe_xMn_y@NC; x:y, representing the molar ratio of Fe:Mn) were successfully prepared via pyrolysis of corresponding precursors containing different metallic salt components. Various morphological, structural, and chemical characterization analysis demonstrate that at an Fe:Mn molar ratio of 3:1, the optimal Fe₃Mn₁@NC material shows high graphitization degree, rich mesoporous structures, a large surface area, and abundant carbon defects/edges, which promote the uniform dispersion of pyridinic-N (pyridinic-N-metal), graphitic-N, carbon oxygen bonds (CO), manganese oxide (MnO) nanocrystals, and Fe₃C NPs-embedded, N-doped carbon sheet (Fe₃C@NC) active sites. In alkaline conditions, the HER onset potentials (E_onset) and potentials recorded at 10 mA cm^-2 (E₁₀) of the optimal Fe₃Mn₁@NC are just 84.8 and 156 mV more negative than those of 20 wt% platinum carbon (Pt/C). Meanwhile, the OER E_onset and E₁₀ values of the optimal Fe₃Mn₁@NC are just 8 and 18.7 mV more positive than those of RuO₂. Furthermore, optimized Fe₃Mn₁@NC catalysts were assembled into a water splitting cell, where the catalytic current density achieves 10 mA cm^-2 at a low voltage of 1.6287 V (with superior catalytic stability), which is just 24.9 mV higher than that of the (-) 20 wt% Pt/C||RuO₂ (+) benchmark (1.6038 V) under the same conditions. This work describes the regulating efficiency of Mn toward growing mesopores and opens new possibilities for the development of novel carbonaceous catalysts with excellent hydroxide catalytic efficiencies based on low cost Mn/Fe elements.

Structural Design Strategy and Active Site Regulation of High-Efficient Bifunctional Oxygen Reaction Electrocatalysts for Zn-Air Battery

Zinc-air batteries (ZABs) exhibit high energy density as well as flexibility, safety, and portability, thereby fulfilling the requirements of power batteries and consumer batteries. However, the limited efficiency and stability are still the significant challenge. Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are two crucial cathode reactions in ZABs. Development of bifunctional ORR/OER catalysts with high efficiency and well stability is critical to improve the performance of ZABs. In this review, the ORR and OER mechanisms are first explained. Further, the design principles of ORR/OER electrocatalysts are discussed in terms of atomic adjustment mechanism and structural design in conjunction with the latest reported in situ characterization techniques, which provide useful insights on the ORR/OER mechanisms of the catalyst. The improvement in the energy efficiency, stability, and environmental adaptability of the new hybrid ZAB by the inclusion of additional reaction, including the introduction of transition-metal redox couples in the cathode and the addition of modifiers in the electrolyte to change the OER pathway, is also summarized. Finally, current challenges and future research directions are presented.

Metal-Organic Framework-Derived Hierarchical MnO/Co with Oxygen Vacancies toward Elevated-Temperature Li-Ion Battery

Transition metal oxides for high-temperature lithium-ion batteries have captivated orchestrated efforts for next-generation high-energy-density anodes. However, due to inherent low tap density, poor conductivity, and structural instability, their poor cyclability capacity and rate performance at elevated temperatures hinder further implementation. Oxygen vacancies (O_v) engineered by manipulating the active sites and electrical conductivity is a promising method for superior lithium storage. Herein, hierarchical MnO/Co nanoparticle-embedded N-doped carbon nanotube (CNT)-assembled carbonaceous micropolyhedrons (O_v-MnO/Co NCPs) are constructed by a "4S" self-assembly, self-template, self-adaptive, and self-catalytic metal-organic framework template method with in situ oxygen vacancies introduced. Impressively, the internal nanoparticles with metallic Co and the external N-doped carbonaceous matrix entangled by fluffy self-generated CNTs synchronously constructed hierarchical micro/nano-secondary hybrids, facilitating highly compacted density, staggered conductive network, multidirectional diffusion pathways, and accelerated electrochemical kinetics. Experimental and density functional theory investigations systematically manifested that the O_v alongside the local built-in electric field within the crystal lattice induced the boosted electrical conductivity, additional active sites, and alleviated structural expansion, further achieving the exceptional diffusivity coefficient and pseudocapacitive capacity. Benefiting from the integrated structural and compositional optimization, the O_v-MnO/Co NCPs achieved distinguished "3C" performance with superior ultralong cyclability (a volumetric capacity of 1713.5 mAh cm^-3 at 1 A g^-1 up to 1000 cycles), good rate capacity (a well-maintained capacity of 670.2 mAh g^-1 even at 10 A g^-1), and considerable high-temperature capability at 60 °C.

Synergistic Interaction of Double/Simple Perovskite Heterostructure for Efficient Hydrogen Evolution Reaction at High Current Density

Electrocatalytic hydrogen production for industrial level requires highly active and cost-effective catalysts at large current densities. Herein A-site Ba-deficient double perovskite PrBa_0.94 Co₂ O_{5+ δ} (PB_0.94 C) is used as a precursor for fabricating PB_0.94 C-based double/simple perovskite heterostructure (PB_0.94 C-DSPH). PB_0.94 C-DSPH with enhanced electrochemical surface area, more hydrophilic surface, and high conductivity ensures abundant active sites, rapid release of gas, and efficient charge transfer at high current densities. The resultant PB_0.94 C-DSPH delivers the overpotential of 364 mV at a current density of 500 mA cm^-2 for hydrogen evolution reaction in 1.0 m KOH solution, along with excellent long-term durability. Promisingly, the electrolyzer with PB_0.94 C-DSPH cathode and NiFe-layered double hydroxide anode demonstrates high performance for overall water splitting by yielding high current density of 500 mA cm^-2 at 1.93 V. Density functional theory calculations indicate that the double/simple perovskite heterostructure promotes the water adsorption, the dissociation of molecular H₂ O, and the OH^* desorption considerably, which controls the whole hydrogen evolution process. The proposed PB_0.94 C-DSPH solves the problem of low hydrogen-evolution efficiency at high current density faced by noble metal-based catalysts in basic environment. This study may provide a route to explore high-demand elements in the earth for addressing the critical catalysts in clean-energy utilizations.

In situ growth of an Fe-doped NiCo-MOF electrocatalyst from layered double hydroxide effectively enhances electrocatalytic oxygen evolution performance

The hierarchical book-like Fe-NiCo-MOF exhibits superior OER performance coupled with outstanding stability at a high current density.

Effects of Structure and Constituent of Prussian Blue Analogs on Their Application in Oxygen Evolution Reaction

The importance of advanced energy-conversion devices such as water electrolysis has manifested dramatically over the past few decades because it is the current mainstay for the generation of green energy. Anodic oxygen evolution reaction (OER) in water splitting is one of the biggest obstacles because of its extremely high kinetic barrier. Conventional OER catalysts are mainly noble-metal oxides represented by IrO2 and RuO2, but these compounds tend to have poor sustainability. The attention on Prussian blue (PB) and its analogs (PBA) in the field of energy conversion systems was concentrated on their open-framework structure, as well as its varied composition comprised of Earth-abundant elements. The unique electronic structure of PBA enables its promising catalytic potential, and it can also be converted into many other talented compounds or structures as a precursor. This undoubtedly provides a new approach for the design of green OER catalysts. This article reviews the recent progress of the application of PBA and its derivatives in OER based on in-depth studies of characterization techniques. The structural design, synthetic strategy, and enhanced electrochemical properties are summarized to provide an outlook for its application in the field of OER. Moreover, due to the similarity of the reaction process of photo-driven electrolysis of water and the former one, the application of PBA in photoelectrolysis is also discussed.

A high-activity bimetallic OER cocatalyst for efficient photoelectrochemical water splitting of BiVO4

BiVO4 has been widely used as a photoanode material, while the slow surface oxygen evolution reaction (OER) kinetics still severely hinders its performance. Here, an efficient bimetallic cocatalyst (named FeSnOS) was obtained by post-annealing a Fe/Sn-containing metal chalcogenide coordination compound to enhance the OER activity of BiVO4. The synergistic effect of Fe and Sn species in the amorphous FeSnOS cocatalyst efficiently lowers the interface impedance of the photoanode, reduces the electrochemical reaction overpotential, and promotes the surface OER dynamics. At the same time, a type-II heterojunction was constructed due to the process of post-annealing, which efficiently improves the bulk phase charge separation efficiency of the photoanode. The obtained optimal photoanode (named FeSnOS-BiVO4) shows a photocurrent density of 3.1 mA cm-2 at 1.23 V vs. the reversible hydrogen electrode, which is 3.4 times higher than that of the pristine BiVO4 photoanode, and its onset potential shifts negatively from 0.44 V to 0.25 V. This work presents a simple and effective method to build a bimetallic cocatalyst for improved photoelectrochemical performance, which extends the application of polymetallic metal chalcogenide complexes.