Non-noble Electrocatalysts Research Articles

Synergistic MoO2@Co3O4 electrocatalysts: A cost-effective approach for efficient alkaline water splitting using electrochemical process

Efficient overall water splitting in alkaline electrolytes remains a critical target for various energy-related applications, necessitating the development of materials having potential of catalyzing hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) simultaneously with high venture and efficiency. This study focuses on the synthesis of affordable non-noble metal-based electrocatalysts using simple and time-efficient methods. Specifically, it highlights the development of MoO2, Co3O4, and MoO2@Co3O4 composite catalysts fabricated via electrodeposition on stainless steel substrates. The synthesized composite materials demonstrated superior electrochemical performance, with the MoO2@Co3O4 composite in a 1:2 M ratio exhibiting significantly enhanced catalytic activity and reduced overpotentials for overall water splitting. The catalyst shows OER and HER activity at 143 mV vs RHE and 177 mV vs RHE over-potentials, which is very low. Also, the catalyst exhibited excellent durability, maintaining stability for up to 23 h in alkaline electrolyte conditions. The synergistic interaction between molybdenum and cobalt oxides was found to facilitate both HER and OER, leading to improved catalytic efficiency at low overpotentials. This approach provides a promising pathway for the integration of robust, cost-effective electrocatalysts, critical for advancing sustainable energy technologies.

Cobalt phosphide nanoarrays on a borate-modified nickel foam substrate as an efficient dual-electrocatalyst for overall water splitting.

Developing efficient non-noble metal dual-functional electrocatalysts for overall water splitting is essential for the production of green hydrogen. Given the significant advantages of self-supporting electrodes, regulating the growth of self-supporting nanoarrays on a conductive substrate is conducive to improving the electrocatalytic activity. In this work, aligned cobalt phosphide (CoP) nanowire arrays grown on borate-modified Ni foam substrate (CoP/R-NF) were utilized as a bifunctional electrocatalyst for both hydrogen evolution reactions (HER) and oxygen evolution reactions (OER) in alkaline solution. The borate interfacial layer regulated the growth behavior of CoP nanowires, promoting a tip-enhanced electric field effect, facilitating an enhanced bimetallic synergistic effect. The CoP/R-NF electrode showed substantial catalytic activity for HER (η10=35 mV, 70mV dec-1) and OER (241 mV, 32mV dec-1). Moreover, a low cell voltage of 1.50V to drive 10mA cm-2 current density for overall water-splitting was achieved in an alkaline water electrolyzer, with long-term durability of 200h at 100mAcm-2, indicating the potential application of CoP/R-NF as a bifunctional catalyst for clean and renewable energy utilization. Such a synthetic strategy could pave the way for the development of non-noble bifunctional electrocatalysts for comprehensive water splitting.

N, F Co-Doped Carbon Derived from Spent Bleaching Earth Waste as Oxygen Electrocatalyst Support.

Affordable nitrogen and fluorine co-doped carbon nanostructure was prepared from the hazardous industrial waste of edible oil refinery, spent bleaching earth (SBE), and used as raw material for obtaining high-performance non-noble metal bifunctional oxygen electrocatalysts. Waste SBE contains 35 % residue non-saturated oil as a carbon source and the assistance of montmorillonite (MMT) as the template. This study converts waste SBE into a fluorine-doped carbon nanostructure through a pyrolysis process followed by removing the aluminosilicate layers of the MMT by HF etching. Furthermore, the impregnation of the support with Co and Fe nitrates readily gives rise to N, F co-doped carbon (NFC) electrocatalysts, as confirmed by XPS analysis. Electrochemical results evidenced that the Co-NFC catalyst proved to be a valuable bifunctional competitor for oxygen reduction reaction and oxygen evolution reaction in alkaline media, showing activity in both reactions and superior stability compared with the Fe-NFC catalyst in accelerated tests. This work offers a straightforward, economical, and eco-friendly strategy for designing N, F co-doped carbon-based electrocatalysts for oxygen reactions in electrochemical devices.

Heterostructuring the CO2-derived Mo2C layer with MoP2 via molten salt electrolysis for efficient hydrogen evolution reaction

Electrochemical fixation of CO2 in molten salts as carbides for catalyzing the hydrogen evolution reaction can contribute to carbon neutrality and value-added conversion of CO2 as well as facilitate the production of sustainable green hydrogen energy. However, the functional ability of the CO2-derived carbides still needs to be substantially improved. Herein, heterostructuring the CO2-derived Mo2C layer with MoP2 is realized via electro-splitting of CO2 in Ca3(PO4)2-containing molten salt. The as-designed Mo2C–MoP2 heterostructure layer presents significantly improved HER performances, namely overpotential being 109 mV @ 100 mA cm−2 and stability for 600 h @ 200 mA cm−2, greatly outperforming both the bare Mo2C layer and commercial Pt candidates. The superior performances of the Mo2C–MoP2 heterostructure are in one way attributed to the modified electronic structure that decrease the energy barrier of the Volmer rate-determining step for HER. In another way, the Mo2C–MoP2 dual-phase increases the hydrophilicity ability of the catalytic layer, accelerating the detachment of the H2 bubbles. The results can provide new insights for both value-added fixation of carbon dioxide and preparation of high-performance non-noble electrocatalyst.

Multi-Criteria selection of Metals-based electrocatalysts for electrochemical ammonia synthesis

The present study employed the Analytic Hierarchy Process (AHP), a renowned method for multi-criteria decision-making, to prioritize electrocatalysts for ammonia synthesis. This process considered the merits and demerits of both noble and non-noble metals electrocatalysts. The evaluation of seven parameters, including economic, lifetime, yield, selectivity, Faradaic efficiency (FE) and potentiometry, determines the justification of alternatives. In addition, there are seven types of electrocatalysts obtained from noble metals electrocatalysts, including Au, Pt, Ru, Rh, Pd, Ir, and Ag, as well as transition metal oxide (TMO), transition metal nitride (TMN), transition metal carbide (TMCA), transition metal chalcogenide (TMc), and other transition metal-based compounds (OTMB), and single atoms (SAs), derived from non-noble metals electrocatalysts, were considered as viable alternatives in light of the objective. According to the results of the multi-criteria evaluation, the criteria of yield, economic value, and lifetime had global weights of 0.306, 0.231, and 0.172, respectively, indicating their significance. Moreover, based on the criteria, Ru with a global weight of 0.189 and non-nobel metals SAs with a global weight of 0.214 are considered the most favored electrocatalysts for ammonia synthesis compared to both noble and non-noble electrocatalysts. The decision-making process considers economic justification (price), reaction yield, lifetime, FE, selectivity and potential as essential criteria, respectively. Ultimately, by closely considering the outcomes of individual atoms, the problems encountered by each catalyst can be effectively addressed, leading to impressive performance.

Catalytic Electrodes for the Oxygen Reduction Reaction Based on Co-Doped Carbon Quantum Dots and Anion Exchange Ionomer

The sluggish kinetics of the oxygen reduction reaction (ORR), more than six orders of magnitude slower than the hydrogen oxidation reaction in acidic conditions, is a major concern for various energy storage and conversion devices, including metal air batteries and fuel cells. The exceptionally high O––O bond energy (~500 kJ/mol) requires generally the use of noble-metal electrocatalysts, including platinum and palladium, for the four-electron reduction in acidic conditions.The ORR is however faster in alkaline medium and non-noble electrocatalysts are applicable, including doped carbon materials. Nanostructured carbons have especially retained the attention due to their solubility in organic solvents that make the drop-casting procedure available. The electroactivity of carbon quantum dots (CQD) for the ORR was demonstrated in 2012.We have recently compared the preparation of CQD by three different methods -pyrolysis, microwave irradiation and hydrothermal synthesis - and reported their respective properties. The hydrothermal method is most promising due to the easily controllable composition and structure via the optimization of precursors and can produce CQD with uniform particle size. We showed especially that the position of nitrogen atoms in the nanostructure, for example in graphitic, pyrrolic or pyridinic sites, changes significantly the properties of the CQD.In this work, we therefore investigate a simple and easily up-scalable synthesis of heteroatom co-doped CQD, using inexpensive starting materials and a fast hydrothermal synthesis procedure, which provides uniform CQD size. The CQD are characterized by various techniques, including XPS, FTIR, and Raman spectroscopy.The overpotential of the ORR contains the activation overpotential that can be reduced by the presence of a potent electrocatalyst improving the charge transfer kinetics, the Ohmic drop and the diffusion overpotential, related to the transport of oxygen gas and of hydroxide ions. Whereas the oxygen diffusion can be facilitated by the microstructure of the electrode, the hydroxide ion transport is enhanced by the presence of an anion exchange ionomer (AEI) in the electrode. The ORR occurs at the triple phase boundary between gas phase (pore), electron conducting catalyst (carbon paper/CQD) and hydroxide ion conductor (AEI), here poly(sulfone trimethylammonium hydroxide) (PSU-TMA).The electrodes investigated in this work are therefore prepared by drop-casting on carbon paper of a slurry containing co-doped CQD and AEI. Impedance spectroscopy and d.c. capacitance measurements are used to determine the electrochemically active surface area of the electrodes. The electrocatalytic activity for the ORR is studied in alkaline conditions (1 M KOH) by cyclic (CV) and linear sweep voltammetry (LSV) at various speeds of a rotating disk electrode (RDE). A.R. Nallayagari, E. Sgreccia, R. Pizzoferrato, M. Cabibbo, S. Kaciulis, E. Bolli, L. Pasquini, P. Knauth, M.L. Di Vona, Tuneable properties of carbon quantum dots by different synthetic methods, J. Nanostruct. Chem. 12 (2022) 565–580. A.R. Nallayagari, E. Sgreccia, L. Pasquini, F. Vacandio, S. Kaciulis , M.L. Di Vona, P. Knauth , Catalytic electrodes for the oxygen reduction reaction based on co-doped (B-N, Si-N, S-N) carbon quantum dots and anion exchange ionomer, Electrochemica Acta 427 (2022) 140861.

NiFeCrMnTiOx As an Active Electrocatalysts for Hydrogen Production from Anion Exchange Membrane (AEM) Saline Water Splitting

Anion exchange membrane (AEM) saline water electrolysis is one of the promising ways to produce green hydrogen at a low cost in the long term. However, suitable electrocatalysts for hydrogen and oxygen evolution reactions for saline water splitting have not yet been figured out. Here, we report a non-noble transition metal-based high entropy oxide nano electrocatalysts Ni0.2Fe0.2Cr0.2Mn0.2Ti0.2Ox for hydrogen and oxygen evolution reactions in saline water electrolysis. The electrocatalysts were synthesized by using co-precipitation technique, further synthesized electrocatalysts were in-situ characterized in X-ray diffraction (XRD), scanning electron microscopy (SEM), Transition electron microscopy (TEM), Raman spectroscopy, and ex-situ characterized in linear sweep voltammetry (LSV), chronopotentiometry, and impedance studies. Further, Membrane Electrode Assembly (MEA) was fabricated, assembled, and tested in a single-cell anion exchange membrane saline water electrolyzer.

NiMn-Layered Double Hydroxides@Metal Anchored Nitrogen-Doped Carbon Framework As a Bifunctional Catalyst for Rechargeable Zinc-Air Batteries

The rechargeable zinc-air battery (ZAB) holds promise as an energy storage system for the next generation due to its high theoretical energy density, safe aqueous electrolyte, environmental friendliness, and cost-effectiveness of zinc. However, the efficiency of ZABs is hindered by the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Noble metals such as platinum (Pt), iridium dioxide (IrO2), and ruthenium oxide (RuO2) are commonly used as advanced electrocatalyst materials. Nonetheless, their scarcity, high cost, unstable catalytic properties, and susceptibility to carbon monoxide poisoning limit the large-scale applications of ZABs.Therefore, exploring non-noble bifunctional electrocatalysts for ZABs is crucial, with transition metals being viable alternatives. Recently, bimetallic transition metal layered double hydroxide (LDH) has emerged as a promising candidate for OER catalysts due to its high specific surface area, abundant active sites, and synergistic effects between two transition metals. However, LDH still faces challenges such as poor electrical conductivity and self-aggregation during fabrication.In this work, we developed a three-dimensional core-shell structure, enabling the growth of LDH on nitrogen-doped porous carbon framework (N-C) materials to address these challenges. The N-C material, derived from zeolitic-imidazole framework (ZIF) material after pyrolysis, shows promise as an ORR catalyst. ZIF, a subclass of metal-organic framework (MOF), boasts high nitrogen content and inherits MOF advantages such as a high surface area, abundant active sites, and chemical stability. Furthermore, utilizing mesoporous silica as a hard template allows us to maintain the dodecahedral structure of ZIF and create mesoporous structures after annealing.The core-shell structure developed in this study demonstrates superior OER and ORR catalytic activity, offering a promising direction for the design of bifunctional catalysts for high-performance ZABs.

Highly Active Ni Incorporated Co2p Heterostructure As Efficient Hydrogen Evolution Reaction Electrode for Alkaline Water Electrolysis

The development of efficient and cost-effective electrocatalyst for the hydrogen evolution reaction (HER) is essential for alkaline water electrolysis. Cobalt phosphide (Co2P) is a promising non-noble electrocatalyst material for HER due to its low cost and high stability in alkaline medium. Nevertheless, the HER activity of Co2P needs to be further improved as compared to noble metal based electrocatalysts. In this study, we have incorporated nickel (Ni) into Co2P using a co-sputtering system for enhanced HER performance, considering the junction of Ni/Co2P heterostructure. This junction serves as dual sites for water dissociation at Ni and hydrogen adsorption/desorption at Co2P, which synergistically enhances the HER activity. We also noticed that Ni concentration influences the heterojunction area as highly active site. Too low or high Ni concentration diminishes active sites by few Ni site formation or Ni agglomeration, respectively. Therefore, precise control over the Ni concentration is essential for maximizing the active site. Our optimized Ni incorporated Co2P sample showed outstanding HER performance with low overpotential of ~77 mV at 10 mA/cm2 and Tafel slope of ~47 mV/dec. The findings of this study will provide insight into the relationship between heterojunction formation and HER performance in transition metal-based heterostructure materials.

Iron-Induced Localized Oxide Path Mechanism Enables Efficient and Stable Water Oxidation.

The sluggish reaction kinetics of the anodic oxygen evolution reaction (OER) and the inadequate catalytic performance of non-noble metal-based electrocatalysts represent substantial barriers to the development of anion exchange membrane water electrolyzer (AEMWE). This study performed the synthesis of a three-dimensional (3D) nanoflower-like electrocatalyst (CFMO) via a simple one-step method. The substitution of Co with Fe in the structure induces a localized oxide path mechanism (LOPM), facilitating direct O-O radical coupling for enhanced O2 evolution. The optimized CFMO-2 electrocatalyst demonstrates superior OER performance, achieving an overpotential of 217 mV at 10 mA cm-2, alongside exceptional long-term stability with minimal degradation after 1000 h of operation in 1.0 M KOH. These properties surpass most of conventional noble metal-based electrocatalysts. Furthermore, the assembled AEMWE system, utilizing CFMO-2, operates with a cell voltage of 1.65 V to deliver 1.0 A cm-2. In situ characterizations reveal that, in addition to the traditional adsorbate evolution mechanism (AEM) at isolated Co sites, a new LOPM occurred around the Fe and Co bimetallic sites. First-principles calculations confirm the LOPM greatly reduced the energy barriers. This work highlights the potential of LOPM for improving the design of non-noble metal-based electrocatalysts and the development of AEMWE.

Interface Engineering of Flower-like Co2P/WO3-x/Carbon Cloth Catalysts with Oxygen Vacancies for Efficient Oxygen Evolution Reaction.

The Constructing an efficient and low-cost oxygen evolution reaction (OER) electrocatalyst is critical for improving the performance of electrolysis in alkaline water. In this study, a self-supported electrocatalyst of flower-like cobalt phosphide and tungsten oxide (Co2P/WO3-x/CC) was prepared on carbon cloth (CC) surface by hydrothermal reaction with solution immersion etching and phosphorization annealing under H2/Ar atmosphere. This strategy can generate oxygen vacancies (OV), improving the speed of charge transfer between cobalt phosphide (Co2P) and tungsten oxide (WO3-x) components. The catalyst greatly increases the electrochemical active surface area, which is beneficial for efficient oxygen evolution. Electrochemical testing studies show that in 1.0 M KOH solution, Co2P-WO3-x/CC catalyst exhibits good OER activity, with a low overpotential of 254 mV at 10 mA cm-2, a small Tafel slope of 58.32 mV dec-1. The synergistic effect of oxygen vacancies and Co2P with WO3-x can regulate electronic structures, expose more active sites, and cooperatively enhancing the OER activity. This study provides a workable strategy for preparing efficient non-noble metal OER electrocatalysts on engineered interfaces and OV.

Construction of CeO2/Co(OH)2/FeS@NF nanosheet arrays for high-performance electrocatalytic oxygen evolution/urea oxidation, and overall water/urea splitting reactions

To develop non-noble electrocatalysts with high activity and stability for oxygen evolution reaction (OER)/urea oxidation reaction (UOR) is crucial to boost the efficiency of overall water/urea splitting reaction (OWS/OUS) for H2 production. Herein, we synthesized novel CeO2/Co(OH)2/FeS nanosheet arrays on nickel foam (CeO2/Co(OH)2/FeS@NF) through a simple two-step hydrothermal and following solvothermal routine. In this special structure, the ultra-thin 2D nanosheet morphology can adequately offer large contact area and thus abundant of active sites, facilitating significantly the mass transfer. Furthermore, the incorporation of FeS into CeO2/Co(OH)2 will not only modify the electron structure but also provide a number of phase interfaces, which can improve the inherent electron conductivity and promote the electron transport. More importantly, the rich oxygen vacancies (Ov) sites can vary the coordination of metal centers, modulating both the charge distribution and M−O bonding strength. As results, the CeO2/Co(OH)2/FeS@NF shows superior low overpotentials of 178 mV/1.30 V at 10 mA cm−2 to OER/UOR. The activity keeps its low value of 232 mV/1.375 V even when the current density was increased to as high as 300 mA cm−2. More importantly, the electrode of CeO2/Co(OH)2/FeS@NF//CeO2/Co(OH)2/FeS@NF just requires a low cell voltage of 1.41 V to realize OUS at a current density of 10 mA cm−2. Specifically, we also realized solar-driven H2 production. Plenty of H2 bubbles were continuously generated with a high speed of 600 L h−1 m−2 on the working electrode surface once the solar panel was placed under the natural sunlight.

Enhanced Electrocatalytic Capacity of Two POM@NH2‐MIL‐101(Fe) Composites for Oxygen Evolution Reaction

AbstractThe development and exploration of efficient bifunctional electrocatalysts for water splitting are in high demand and have garnered significant attention in recent years. Herein, by incorporating the advantages of catalytically active polyoxometalates (POMs) and structural stable metal–organic frameworks (MOFs), two POM@MOFs composite materials, Ni4Mo12@Fe and Co4Mo12@Fe, have been successfully prepared via the encapsulation of POMs anions, [MoV12O30(μ2‐OH)10H2{NiII4(H2O)12}]∙14H2O (noted as Ni4Mo12) and [MoV12O30(μ2‐OH)10 H2{CoII(H2O)3}4]∙12H2O (noted as Co4Mo12), into the cavities of MOFs NH2‐MIL‐101(Fe), respectively. Compared to each individual components, Ni4Mo12@Fe and Co4Mo12@Fe composites, as heterogeneous electrocatalysts, both showed enhanced electrocatalytic capacities for efficient oxygen evolution reaction (OER) under alkaline conditions with overpotentials of 332.64 mV for Ni4Mo12@Fe and 352.64 mV for Co4Mo12@Fe at 10 mA cm−2. Additionally, the enhanced electrocatalytic capacities of these two composites could also achieve towards hydrogen evolution reaction (HER). Such a POMs‐assisted strategy for the formation of POM@MOFs composites, described here, paves a new avenue for the development of highly economical, active nonnoble metal bifunctional electrocatalysts for OER and HER.

ZIF-67 derived N doped carbon embedded CoxP for superior hydrogen evolution

Abstract Developing a sustainable non-noble hybrid electrocatalyst for effective electrocatalysis is the most crucial task; particularly in sustainable hydrogen energy production in the realm of energy conversion. In this work, effective thermal pyrolysis process followed by phosphorization strategy was employed to prepare and fabricate ZIF-67 (Zeolitic imidazole) assisted Co2P/N doped carbon electrocatalyst for hydrogen evolution reaction (HER). The optimized Co2P/N–C electrocatalyst exhibited hollow porous nanostructures as confirmed from the scanning electron microscopy. The achieved porous nanostructure improved the efficiency of the charge and mass transportation which is confirmed by the BET analysis, has high surface area value of 94.731 m2/g. In addition, a transition metal atom can regulate reactants adsorption and desorption capacity by modulating Co and P electronic configuration. The electrochemical studies of fabricated ZIF-67 derived Co2P/N–C electrode were analyzed using 1.0 M alkaline potassium hydroxide (KOH) medium in 3 electrode system process. Whilst, optimizing the pyrolysis temperature during the phosphorization will remarkably enhance the favourable characteristics of the hydrogen generation. Notably, the optimized ZIF-67 derived Co2P/NC at 350 °C electrode exhibited low overpotential (135 mV) at minimum 10 mA/cm2 and low 120.3 mV/dec Tafel slope. Besides, electrode stability at 10 mA/cm2 current density was verified by chronoamperometry test. Hence, this study furnishes the potential technique for the development of advanced hybrid MOF electrocatalyst as a successful alternative on large scale.

Na-doped cobalt spinel electrocatalysts prepared by programmed electrostatic spraying for improving OER activity and durability in acidic media

The daunting challenge to establish a trade-off among the activity, durability, and cost of electrocatalysts for oxygen evolution reaction (OER) with sluggish reaction kinetics impedes the practical green energy conversion. Hereby, a non-noble metal-based electrocatalyst (i.e., Na-doped Co3O4) was in-situ prepared by programmed electrostatic spraying as an advanced alternative to the costly and scarce state-of-the-art IrO2 and RuO2-based electrocatalysts. The utilization of this sprayer facilitates intimate contact with the substrate electrode and provides short ion diffusion paths, facilitating efficient electron transport. Additionally, the doping of Na ions into the Co3O4 structure results in structural distortion and charge redistribution, leading to the generation of oxygen vacancies (OVs). These OVs enhance the activity of lattice oxygen atoms, thus enabling rapid and durable oxygen evolution in an acidic media (0.5 M H2SO4). The optimal Na-Co3O4 (AA) exhibits a notably low overpotential of 360 mV@10 mA·cm−2 and at least 200 h stability. In addition, density functional theory (DFT) calculations confirm that the incorporation of Na ions significantly elevates electrical conductivity by decreasing the energy band gap and reduces the free energy barrier for the conversion of *O to *OOH, thereby improving the intrinsic OER activity. Finally, by implanting the catalyst in a single-cell proton exchange membrane water electrolyzer (PEMWE), the current density of 100 mA·cm−2 is achieved at a voltage of 1.62 V. This innovative non-noble metal catalyst holds great potential for scalable PEMWE anodes.

Chirality Engineering of Nanostructured Copper Oxide for Enhancing Oxygen Evolution from Water Electrolysis.

The exploration of a new conceptual strategy for improving the oxygen evolution reaction (OER) of earth-abundant electrocatalysts is critical. In this study, chiral copper oxide nanoflower is explored by a self-assembly method. The characterization suggests the chiral structure originates from the crystal plane-level helical stack of the secondary nanosheets. Of note, the assembly illustrates a record-high degree of spin polarization of 96%, indicating the ideal alignment of electron spin. Moreover, density function theory calculations show the chiral structure reducing the reaction energy barrier (REB) while switching the potential-determining step from *O→*OOH to *OH→*O. Together with the enhanced electrochemical active surface area and accelerated charge transfer, the production of ground-state triplet O2 is improved via a spin-forbidden route that involves the singlet H2O/OH•. Consequently, the chiral nanoflower shows a overpotential of 308mV at 10mA cm-2 and a Tafel slope of 93.5mV dec-1, which is even superior to the commercial RuO2 (310mV, 101mV dec-1). This study presents a new strategy for improving the OER activity by simultaneously enhancing electronic properties and lowering the REB of an non-noble electrocatalyst via chirality engineering.

Innovative Air Cathode with Ni-Doped Cobalt Sulfide in Highly Ordered Macroporous Carbon Matrix for Rechargeable Zn-Air Battery.

To realize the practical application of rechargeable Zn-Air batteries (ZABs), it is imperative to develop a non-noble metal-based electrocatalyst with high electrochemical performance for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, Ni-doped Co9S8 nanoparticles dispersed on an inverse opal-structured N, S co-doped carbon matrix (IO─NixCo9-xS8@NSC) as a bifunctional electrocatalyst is presented. The unique 3D porous structure, arranged in an inverse opal pattern, provides a large active surface area. Also, the conductive carbon substrate ensures the homogeneous dispersion of NixCo9-xS8 nanocrystals, preventing aggregation and increasing the exposure of active sites. The introduction of heteroatom dopants into the Co9S8 structure generates defect sites and enhances surface polarity, thereby improving electrocatalytic performance in alkaline solutions. Consequently, the IO─NixCo9-xS8@NSC shows excellent bifunctional activity with a high half-wave potential of 0.926V for ORR and a low overpotential of 289mV at 10mA cm-2 for OER. Moreover, the rechargeable ZAB assembled with prepared electrocatalyst exhibits a higher specific capacity (768 mAh gZn -1), peak power density (180.2mW cm-2), and outstanding stability (over 160h) compared to precious metal-based electrocatalyst.

Ultrafast synthesis of biphase Ni-doped FeOOH for efficient and stable oxygen evolution at high current density

NiFe oxyhydroxides, generally reconstructed on surface during oxygen evolution reaction (OER), are real active species for water oxidation; however, their direct and convenient preparation remains challenging. Here, we develop a one-step approach to prepare biphase (α/δ) Ni-doped FeOOH catalyst in 3 min under room temperature. The core of this ultrafast method is that Fe2+ derived from the redox reaction of Fe3+ and Ni2+ accelerate Fenton-like reaction, while simultaneously producing mixed-valence Ni ions(Ni2+, Ni3+) results in not only homovalent and heterovalent doping, but also biphase Ni-doped FeOOH heterojunction with high and low crystallinity. Specifically, Ni2+ doping leads to a preferred formation of low-crystalline δ-oriented Ni-doped FeOOH with abundant oxygen vacancies, which is in favor of triggering the lattice oxygen mechanism (LOM) during OER. Benefitting from high/low crystalline biphase heterojunction and LOM, the optimized Ni-FeOOH merely needs low overpotential of 300 mV to reach 1000 mA cm−2 for OER in alkaline electrolyte and also shows excellent durability even at a high current density of 500 mA cm−2. This work provides a cost-effective strategy to fabricate highly active and robust non-noble electrocatalysts that can potentially be applied for industrial-scale OER electrolysis.

Bimetal Metaphosphate/Molybdenum Oxide Heterostructure Nanowires for Boosting Overall Freshwater/Seawater Splitting at High Current Densities.

Exploring excellent non-noble bifunctional electrocatalysts for freshwater/seawater splitting at high current densities has attracted extensive interest owing to strong anodic oxidation and severe chloride corrosion challenges. Herein, hierarchical bimetal Ni-Co metaphosphate/molybdenum oxide heterostructure nanowires (NiCoMoPO) are rationally designed and fabricated to efficiently boost oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline freshwater/seawater, where the favorable electronic structure from heterostructures, signified by X-ray absorption spectra, endows NiCoMoPO with the enhanced intrinsic activity, while its hierarchical nanowire structure and heterostructures provide abundant active sites. Additionally, the PO3 - improves the chloride-corrosion resistance and efficiently facilitates the OER kinetics verified by theoretical and experimental studies. Therefore, NiCoMoPO drives 1000mA cm-2 at low overpotentials of 467 and 442mV for OER and HER in alkaline freshwater respectively, as well as a small cell voltage of 2.135V for overall freshwater splitting with robust durability of 300h. Impressively, due to the strong corrosion resistance, at 500mA cm-2 of overall seawater splitting, NiCoMoPO maintains almost 2.096V for 1200h, indicating promising practical applications. This work sheds light on the rational design and fabrication of outstanding electrocatalysts at high current densities of seawater/freshwater splitting.

Complementary Multisite Turnover Catalysis toward Superefficient Bifunctional Seawater Splitting at Ampere-Level Current Density.

The utilization of seawater for hydrogen production via water splitting is increasingly recognized as a promising avenue for the future. The key dilemma for seawater electrolysis is the incompatibility of superior hydrogen- and oxygen-evolving activities at ampere-scale current densities for both cathodic and anodic catalysts, thus leading to large electric power consumption of overall seawater splitting. Here, in situ construction of Fe4N/Co3N/MoO2 heterostructure arrays anchoring on metallic nickel nitride surface with multilevel collaborative catalytic interfaces and abundant multifunctional metal sites is reported, which serves as a robust bifunctional catalyst for alkaline freshwater/seawater splitting at ampere-level current density. Operando Raman and X-ray photoelectron spectroscopic studies combined with density functional theory calculations corroborate that Mo and Co/Fe sites situated on the Fe4N/Co3N/MoO2 multilevel interfaces optimize the reaction pathway and coordination environment to enhance water adsorption/dissociation, hydrogen adsorption, and oxygen-containing intermediate adsorption, thus cooperatively expediting hydrogen/oxygen evolution reactions in base. Inspiringly, this electrocatalyst can substantially ameliorate overall freshwater/seawater splitting at 1000mA cm-2 with low cell voltages of 1.65/1.69V, along with superb long-term stability at 500-1500mA cm-2 for over 200 h, outperforming nearly all the ever-reported non-noble electrocatalysts for freshwater/seawater electrolysis. This work offers a viable approach to design high-performance bifunctional catalysts for seawater splitting.