Electrocatalysts For Water Splitting Research Articles

Cobalt-iron Co-doped ammonium phosphomolybdate for electrocatalytic oxygen evolution in acidic electrolyte

In this study, we investigate the performance of cobalt-iron co-doped phosphomolybdate (CoFe–PMo) as an efficient electrocatalyst for oxygen evolution reaction (OER) in acidic electrolyte. We demonstrate that the introduction of cobalt and iron ions into the phosphomolybdate structure enhances its catalytic activity towards OER. The electrochemical measurements reveal that CoFe–PMo exhibits remarkable stability and improved catalytic activity compared to the undoped amminium phosphomolybdate. The overpotential for OER is only 223 mV at 10 mA cm−2, which is even smaller than that of IrO2.The durable tests maintain its performance over 40 h electrolysis period that the current barely drops. This enhanced performance is attributed to the internal redox between doped cobalt-iron ions and Mo ions in PMo, which promotes the charge transfer and enhances the active sites for OER. The results suggest that CoFe–PMo is a promising catalyst for efficient water splitting in acidic electrolyte, highlighting the potential of cobalt-iron co-doped ammonium phosphomolybdate as a cost-effective and durable electrocatalyst for water splitting for H2 energy in acidic electrolytes.

CoFe phosphide conversion to heterojunction metal phosphide (CoFeP) electrocatalysts for water splitting

Many researchers have made efforts on designing and synthesizing catalytic active site as well as deciphering how exactly they catalyze the reaction to obtain electrocatalysts with superior water splitting activity. However, the development of high-performance dual-functional non-precious metal electrocatalysts for Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) remains challenging. In this study, CoFe undergoes in a one-step phosphorylation reaction converted to Fe2P, CoP2 and Co2P, abbreviated as heterojunction metal phosphide (CoFeP). The Co/Fe ratio can be flexibly adjusted by controlling the content of Co in the synthesis process, which results in CoFeP with different morphologies. Benefiting from the porous structure and higher catalytic active sites, the Co-0.0032-FeP presents a lower overpotential of 127 mV and 266 mV for HER and OER of 10 mA cm−2 in a KOH solution, respectively. In addition, the low Tafel Slope and stable current density of Co-0.0032-FeP indicate fast kinetics and high stability in the HER.

Design and construction of 3D porous hierarchical structure Ni–Fe–Co bifunctional catalyst toward highly efficient overall water splitting

Developing high performance, cost-effective, non-precious metal electrocatalysts for overall water splitting (OWS) still remains a serious challenge. Heterostructures comprised of multiple metals possess significant potential to enhance OWS owing to the prominent synergistic effects between different components. Herein, we successfully fabricated NiFeCoPSO and Co(OH)2/NiFeSO structures with a three-dimensional (3D) porous hierarchical structure, using carbon cloth (CC) as a substrate. The innovative 3D hierarchical structure ensures that numerous active sites are extensively exposed, thus guaranteeing competent contact between the active reaction centers and the reactant. As a result, the obtained NiFeCoPSO displays outstanding hydrogen evolution reaction (HER) ability (102 mV for a current density of 10 mA cm−2), while the intermediate product Co(OH)2/NiFeSO exhibits excellent oxygen evolution reaction (OER) performance (231 mV for 10 mA cm−2). Furthermore, the dual electrode system assembled using NiFeCoPSO cathode and Co(OH)2/NiFeSO anode presents excellent overall water splitting (OWS) behavior (1.55 V for 10 mA cm−2). This research offers a cost-effective transition metal phosphide-sulfide electrocatalyst and its synthesis method for OWS.

Structural investigation of Cr2CTx/NiFe2O4 MXene composite as a bifunctional electrocatalyst for water splitting

The electrocatalytic water splitting offers great potential as an environmentally friendly and sustainable method to produce hydrogen and oxygen, the former serving as a renewable alternative to traditional fossil fuels. MXene, a novel two-dimensional (2D) layered class of materials, has gained enormous attention as an electrocatalyst for water splitting. This versatile material can be tailored to enhance its electroactive surface sites and stability toward electrocatalytic performance. Herein, we have designed a 2D hybrid material, Cr2CTx/NiFe2O4, via an in-situ hydrothermal approach. NiFe2O4 spheres decorated on layered-Cr2CTx are subjected to analysis using XRD, FTIR, TGA, XPS, FESEM, HRTEM-SAED, and optical profilometry. The synthesized hybrid MXene material shows outstanding activity for overall water splitting compared to Cr2CTx and NiFe2O4. Cr2CTx/NiFe2O4 exhibits an overpotential of 144 mV and 159 mV at a current density of 10 mA cm−2 for hydrogen evolution and oxygen evolution reactions, respectively, and achieves a cell potential of 1.69 V for overall water splitting. This study reveals valuable insights on bi-functional 2D hybrid MXene materials for electrocatalytic water splitting.

Modulation strategies of electrocatalysts for 5-hydroxymethylfurfural oxidation-assisted water splitting

To address energy shortages and environmental issues, prioritizing renewable energy development and usage is crucial. Employing renewable sources for water electrolysis offers a sustainable method for hydrogen generation. Reducing the water electrolysis potential is vital for efficient clean energy conversion and storage. Substituting the anodic oxygen evolution reaction in conventional hydrogen production from water electrolysis with the more thermodynamically favorable 5-hydroxymethylfurfural (HMF) oxidation reaction can greatly decrease overpotential and yield the valuable product 2,5-furan dicarboxylic acid. The key to this process is developing effective electrocatalysts to minimize the potential of the HMF electrooxidation-hydrogen production system. Therefore, this review provides a comprehensive introduction to the modulation strategies that affect the electronic and geometric structure of electrocatalysts for HMF oxidation-assisted water splitting. The strategies encompass heteroatom doping, defect projection, interface engineering, structural design, and multi-metal synergies. The catalysts are assessed from various angles, encompassing structural characterization, reaction mechanisms, and electrochemical performance. Finally, current challenges in the catalyst design and potential development of this promising field are proposed.

Component regulation in flower-like FexCoNiP/C nanohybrids as bifunctional efficient electrocatalysts for overall water splitting

Incorporating bi-metal transition metal phosphides (TMPs) with high-valent metal is a powerful method to obtain highly efficient and low-cost bifunctional electrocatalysts in alkaline media for overall water splitting. However, the composition-activity relationship of such incorporation has not been investigated yet due to the challenge in constructing tri-metal TMPs with continuously variable composition while maintaining a homogenous elemental distribution. In this study, we proposed a strategy using a trimetal oleta composite with a homogenous elemental distribution at the molecular scale as an ideal precursor. This precursor was then used to fabricate Fe-incorporated Ni-Co phosphide on a flower-like carbon substrate, resulting in a continuously changeable Fe content (FexNiCoP/C). Benefiting from the fully exposed structure and the incorporation of Fe, the flower-like FexNiCoP/C hybrids exhibited excellent electrocatalytic performance for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). By optimizing the Fe content, the flower-like Fe0.4NiCoP/C hybrid achieved 10 mA/cm2 at a low overpotential of 243 mV for the OER and 107 mV for the HER, respectively. When the optimal Fe0.4NiCoP/C electrodes were employed as the anode and cathode for water electrolysis in an alkaline electrolyte, the electrolyzer achieved 10 mA/cm2 at a low cell voltage of 1.59 V. This work provides an inexpensive, highly active, and durable electrocatalyst, while revealing the composition-activity relationship of FexNiCoP/C for overall water splitting in alkaline media.

Metal-organic framework derived heterostructured phosphide bifunctional electrocatalyst for efficient overall water splitting

Developing high active and stable cost-effective bifunctional electrocatalysts for overall water splitting to produce hydrogen is of vital significance in clean and sustainable energy development. This work has prepared a novel porous unreported MOF (Ni-DPT) as a precursor to successfully synthesize a non-noble bifunctional NiCoP/Ni12P5@NF electrocatalyst through doping strategy and interface engineering. This catalyst is constructed by layered self-supporting arrays with heterojunction interface and rich nitrogen-phosphorus doping. Structural characterizations and the density function theory (DFT) calculations confirm that the interface effect of NiCoP/Ni12P5 heterojunction can regulate the electronic structure of the catalyst to optimize the Gibbs free energy of hydrogen (ΔGH*); simultaneously, the defect-rich layered nanoarrays can expose more active sites, shorten mass transfer distance, and generate a self-supporting structure for in-situ reinforcing the structural stability. As a result, this NiCoP/Ni12P5@NF catalyst exhibits favorable electrocatalytic performance, which simply needs overpotentials of 100 mV for HER and 310 mV for OER, respectively, at a current density of 10 mA·cm−2. The anion exchange membrane electrolyzer assembled with this NiCoP/Ni12P5@NF as both anode and cathode catalysts can operate stably for 200 h at a current density of 100 mA·cm−2 with an insignificant voltage decrease. This work may provide some inspiration for the further rational design of inexpensive non-noble multifunctional electrocatalysts and electrode materials for water splitting to generate hydrogen.

Introducing oxygen vacancies to tune cobalt oxide by Mn doped for high-effective overall water-splitting

The design of efficient bifunctional electrocatalysts for overall water splitting is an essential task for the production of hydrogen. Co3O4 has been developed as highly efficient OER electrocatalysts but with almost no activity for HER. The formation of oxygen vacancies in Co3O4 could significantly enhance the OER and HER activity, Mn-doping are relatively infrequent in this field. In this work, Co3O4 is modified by doping Mn to introduced oxygen vacancies for high-efficiency water splitting performance. The Mn doped Co3O4 shows excellent performance towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with a low overpotential at 10 mA·cm−2 of 157 mV and 265 mV, and an applied potential of 1.54 V at 10 mA·cm−2. The excellent electrocatalytic performance is mainly attributed to oxygen vacancies in Co3O4, rational adjustment of the electronic structure of active sites to increase the intrinsic activity of Co3O4. The Mn doped Co3O4 can be a promising bifunctional electrocatalyst for overall water splitting.

Multiple strategies regulating the d-band center of Ni2P/NiFe2O4 @N-GTs hierarchical nanoarchitecture as efficient electrocatalyst for overall water splitting

The rational design of highly active electrocatalysts for water electrolysis remains challenging for green hydrogen utilization. Herein, guided by the correlation between the electroactivity and the d-band center (Ed), a novel hierarchical nanoarchitecture (Ni2P/NiFe2O4-VO@N-GTs) was fabricated, in which, Ni2P nanoparticles are grown on the oxygen vacancy-rich NiFe2O4 nanosheet arrays anchoring on N-doping graphene tubes. The results reveal that the multiple strategies including the vacancies and heterogeneous interface construction effectively induce the charge redistribution, and further adjust the Ed to the appropriate energy level, which endows the optimal balance between the adsorption and desorption ability of the catalyst to reaction intermediates, thus leading to the conspicuous electrocatalytic activity. Additionally, the hierarchical nanoarchitecture contributes to the exposure of more active sites, the efficiency of electron transfer, and the release of generated gas. Hence, Ni2P/NiFe2O4-VO@N-GTs presents superior bifunctional activity, especially a low overpotential of 194 mV at 10 mA cm−2 for OER. The corresponding overall water electrolyzer owns a lower cell voltage and long-term durability with continuously operating over 330 h at 100 mA cm−2, outperforming the most reported bifunctional electrocatalysts. This work presents an effective pathway for regulating the Ed through multiple strategies to improve the catalytic performance of catalysts.

Covalent versus noncovalent attachments of [FeFe]‑hydrogenase models onto carbon nanotubes for aqueous hydrogen evolution reaction

In an effort to develop the biomimetic chemistry of [FeFe]‑hydrogenases for catalytic hydrogen evolution reaction (HER) in aqueous environment, we herein report the integrations of diiron dithiolate complexes into carbon nanotubes (CNTs) through three different strategies and compare the electrochemical HER performances of the as-resulted 2Fe2S/CNT hybrids in neutral aqueous medium. That is, three new diiron dithiolate complexes [{(μ-SCH2)2N(C6H4CH2C(O)R)}Fe2(CO)6] (R = N-oxylphthalimide (1), NHCH2pyrene (2), and NHCH2Ph (3)) were prepared and could be further grafted covalently to CNTs via an amide bond (this 2Fe2S/CNT hybrid is labeled as H1) as well as immobilized noncovalently to CNTs via π-π stacking interaction (H2) or via simple physisorption (H3). Meanwhile, the molecular structures of 1–3 are determined by elemental analysis and spectroscopic as well as crystallographic techniques, whereas the structures and morphologies of H1-H3 are characterized by various spectroscopies and scanning electronic microscopy. Further, the electrocatalytic HER activity trend of H1 > H2 ≈ H3 is observed in 0.1 M phosphate buffer solution (pH = 7) through different electrochemical measurements, whereas the degradation processes of H1-H3 lead to their electrocatalytic deactivation in the long-term electrolysis as proposed by post operando analysis. Thus, this work is significant to extend the potential application of carbon electrode materials engineered with diiron molecular complexes as heterogeneous HER electrocatalysts for water splitting to hydrogen.

Enhanced activity of electrodeposited WO3 thin films as bi-functional electrocatalysts for water splitting

The ultimate goal of the hydrogen economy is to develop an efficient and cost-effective electrocatalyst that can accelerate hydrogen synthesis from water without or with little additional energy. This study describes a unique surface modified electrodeposited nano-sized tungsten oxide (WO3) as an intriguing bi-functional electrocatalyst for OER in alkaline and HER in acidic conditions. The nano-WO3 was synthesized hydrothermally and electrodeposited on a fluorinated tin oxide (FTO) electrode. The highly uniform distribution of the WO3@FTO catalyst results in negligible charge transfer resistance, a large electroactive surface area, and increased water-splitting potential. During oxygen evolution reaction (OER), electrodeposited WO3@FTO initiates water splitting at an overpotential (η) of just 240 mV and represents a turnover frequency (TOF) of 0.59 sec−1. These results are comparable to previously reported electrocatalysts. Under an alkaline electrolyte, a current density of 15 mA/cm2 remained constant for several hours, indicating the high stability and durability of the electrodeposited WO3@FTO electrode. The electrode also performed well in hydrogen evolution reactions (HER). A Tafel slope of 46 mV/dec and −28 mV/dec was found for OER and HER, respectively, indicating an enhanced kinetics rate of reaction taking place at the electrode surface. Furthermore, in acidic conditions, the electrode represents a lower HER overpotential of 104 mV. The work provides a significant understanding of electrodeposited WO3@FTO electrodes and their role in electrochemical water splitting.

Unlocking Efficiency: Minimizing Energy Loss in Electrocatalysts for Water Splitting.

Catalysts play a crucial role in water electrolysis by reducing the energy barriers for hydrogen and oxygen evolution reactions (HER and OER). Research aims to enhance the intrinsic activities of potential catalysts through material selection, microstructure design, and various engineering techniques. However, the energy consumption of catalysts has often been overlooked due to the intricate interplay among catalyst microstructure, dimensionality, catalyst-electrolyte-gas dynamics, surface chemistry, electron transport within electrodes, and electron transfer among electrode components. Efficient catalyst development for high-current-density applications is essential to meet the increasing demand for green hydrogen. This involves transforming catalysts with high intrinsic activities into electrodes capable of sustaining high current densities. This review focuses on current improvement strategies of mass exchange, charge transfer, and reducing electrode resistance to decrease energy consumption. It aims to bridge the gap between laboratory-developed, highly efficient catalysts and industrial applications regarding catalyst structural design, surface chemistry, and catalyst-electrode interplay, outlining the development roadmap of hierarchically structured electrode-based water electrolysis for minimizing energy loss in electrocatalysts for water splitting.

NiMoO4 containing O-vacancy cooperated with bimetallic sulfides as efficient bifunctional electrocatalyst for overall water splitting

MoS2 is a potential transition metal sulfide (TMS) with excellent performance for hydrogen evolution reaction (HER) in acidic medium. However, MoS2 has poor stability owing to its metastable properties and therefore is easily oxidized to MoO3 which can hinder the HER process. In this work, MoO3 on the surface of the TMS is transformed to NiMoO4 with plentiful oxygen vacancies (Ov) favorable for HER and oxygen evolution reaction (OER) by an acid treatment to form an Ov-containing transition bimetallic sulfide/oxide catalyst (Ov-NiMoO4@Ni3S2-MoS2-rGO-NF, denoted as NiMoO4@NiMoS-rN). The electrocatalyst shows exceptional performance for HER and OER in terms of increased intrinsic activity, electron transfer efficiency, reaction kinetics and durability on account of the Ov, synergistic effect among different phases and bimetallic active sites. The overpotentials of NiMoO4@NiMoS-rN electrode when achieving 10 mA cm−2 are 45 mV and 195 mV towards HER and OER in alkaline, respectively, and the performance holds nearly unchanged during a 50-h stability test. When assembled to a two-electrode system, the current density of 10 mA cm−2 can keep steady for 50 h without degradation. The strategy combined by phase transition, interface and defect engineering via a facile method provides a practical idea for design and modulation of bifunctional electrocatalysts.

Synergistic Mo and W single atoms co-doped surface hydroxylated NiFe oxide as bifunctional electrocatalysts for overall water splitting

Two novel defect engineering strategies, surface hydroxylation and single atom (SA) doping, are explored to fabricate a high performance bifunctional water electrolysis catalyst, synergistic Mo and W SAs co-doped surface hydroxylated NiFe oxide (FN-MoWact). The product catalyst achieves ultralow overpotentials of 196 and 246 mV for oxygen evolution reaction (OER) and decent overpotentials of 79 and 246 mV for hydrogen evolution reaction (HER) at current densities of 10 and 500 mA cm−2, respectively. For overall water splitting, the FN-MoWact//FN-MoWact couple requires ultralow cell voltages of 1.504 and 1.729 V to deliver current densities of 10 and 500 mA cm−2, respectively, and remains stable after a 100-hour operation at an initial current density of 534 mA cm−2. The enhanced electrocatalytic activities are attributed to surface hydroxylation and doping of synergistic Mo and W SAs. The two defect engineering modifications, as supported by analyses of density functional theory calculations and in-situ X-ray absorption spectroscopy, lead to a proper reduction in metal-oxygen covalency, thus minimizing the energy difference of the rate-determining step of the OER process, and create surface active sites with a d-band center located closer to the Fermi level, thus properly strengthening proton binding to enhance HER activities.

Exsolved Ru-mediated stabilization of MoO2-Ni4Mo electrocatalysts for anion exchange membrane water electrolysis and unbiased solar-driven saline water splitting

Molybdenum-based electrocatalysts remain the exclusive and practical option for anion exchange membrane water electrolysis (AEMWE) due to their exceptional catalytic activity in the alkaline hydrogen evolution reaction (HER). However, they are limited by low electrochemical stability resulting from the dissolution into MoO42- ions in alkaline conditions, leading to secondary phase precipitation that hinders the surface reaction. Here, we demonstrate Ru-mediated electrochemical stabilization of MoO2-Ni4Mo electrocatalysts, which exhibit exceptionally enhanced durability as well as catalytic activity, enabling ampere-level current density water splitting in saline water. Theoretical calculations and ex-situ X-ray absorption spectroscopy reveal that exsolved Ru nanoclusters with a higher hydroxyl affinity significantly establish a local hydroxide-deficient environment, leading to the stabilization of MoO2. Consequently, Ru-MoO2-Ni4Mo exhibits outstanding hydrogen production with stable operation for over 300 h to achieve a current density of 1.0 A cm−2 and a record-high solar-to-hydrogen efficiency of 22.5 % in AEMWE and photovoltaic-assisted water splitting system, respectively.

Synergistic doping of Iron and selenium on nickel hydroxide nitrate nanoarrays-derived as an efficient electrocatalyst for overall water splitting

The fabrication of highly efficient and stable catalysts for water oxidation is important to promote the development of the hydrogen fuel industry. In this study, dual-element-doped two-dimensional nickel hydroxide nitrate nanoarrays (NiHN) self-supported on nickel foam were fabricated via a facile electrodeposition process. The results demonstrated that Fe and Se were incorporated into the nickel hydroxide structure. The binder-free FeSe-NiHN catalyst exhibited low overpotentials of 129 and 250 mV at 10 mA cm−2 for the hydrogen evolution reaction and at 100 mA cm−2 for the oxygen evolution reaction in 1 M KOH media, respectively. Furthermore, a durability test conducted at 70 mA cm−2 for 28 h showed no evident degradation of the catalyst activity, verifying its exceptional stability. Thus, FeSe-NiHN is a potential water splitting electrocatalyst for inexpensive hydrogen production.

Catalytic Water Electrolysis by Co-Cu-W Mixed Metal Oxides: Insights from X-ray Absorption Spectroelectrochemistry.

Mixed metal oxides (MMOs) are a promising class of electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Despite their importance for sustainable energy schemes, our understanding of relevant reaction pathways, catalytically active sites, and synergistic effects is rather limited. Here, we applied synchrotron-based X-ray absorption spectroscopy (XAS) to explore the evolution of the amorphous Co-Cu-W MMO electrocatalyst, shown previously to be an efficient bifunctional OER and HER catalyst for water splitting. Ex situ XAS measurements provided structural environments and the oxidation state of the metals involved, revealing Co2+ (octahedral), Cu+/2+ (tetrahedral/square-planar), and W6+ (octahedral) centers. Operando XAS investigations, including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), elucidated the dynamic structural transformations of Co, Cu, and W metal centers during the OER and HER. The experimental results indicate that Co3+ and Cu0 are the active catalytic sites involved in the OER and HER, respectively, while Cu2+ and W6+ play crucial roles as structure stabilizers, suggesting strong synergistic interactions within the Co-Cu-W MMO system. These results, combined with the Tafel slope analysis, revealed that the bottleneck intermediate during the OER is Co3+ hydroperoxide, whose formation is accompanied by changes in the Cu-O bond lengths, pointing to a possible synergistic effect between Co and Cu ions. Our study reveals important structural effects taking place during MMO-driven OER/HER electrocatalysis and provides essential experimental insights into the complex catalytic mechanism of emerging noble-metal-free MMO electrocatalysts for full water splitting.

Heterogeneous Cr-doped Co3S4/NiMoS4 bifunctional electrocatalyst for efficient overall water splitting

Exploration of efficient and robust catalysts for electrocatalytic water splitting is paramount yet challenging for economical hydrogen production. Here, nanoforest-like heterostructures composed of inner NiMoS4 nanowires and outer Cr-doped Co3S4 nanosheets were grown on nickel foams (Cr–Co3S4/NiMoS4) as highly efficient bifunctional electrocatalysts. As a result, Cr–Co3S4/NiMoS4 heterostructures exhibit low overpotentials of 72 mV and 243 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at 10 mA cm−2, respectively. Moreover, the water electrolyzer assembled by Cr–Co3S4/NiMoS4 as bifunctional electrodes reaches 10 mA cm−2 at 1.587 V and maintains exceptional stability over 200 h. The experimental and theoretical characterizations collectively unveil that the charge redistribution occurs at the heterointerface between Cr-doped Co3S4 and NiMoS4, resulting in the regulation of both their electronic structures, which optimizes the adsorption of HER intermediates and decreases the energy barrier of determining step for OER. Additionally, the Cr doping and nanoforest-like morphology increase the intrinsic conductivity and the exposure of active sites, collectively improving the water electrolysis efficiency. This finding presents a promising way to construct and adjust the heterojunction engineering for bifunctional electrocatalysts toward water electrolysis.

Electrocatalytic Properties of Quasi-2D Oxides LaSrMn0.5M0.5O4 (M = Co, Ni, Cu, and Zn) for Hydrogen and Oxygen Evolution Reactions.

Designing cost-effective and highly efficient electrocatalysts for water splitting is a significant challenge. We have systematically investigated a series of quasi-2D oxides, LaSrMn0.5M0.5O4 (M = Co, Ni, Cu, Zn), to enhance the electrocatalytic properties of the two half-reactions of water-splitting, namely oxygen and hydrogen evolution reactions (OER and HER). The four materials are isostructural, as confirmed by Rietveld refinements with X-ray diffraction. The oxygen contents and metal valence states were determined by iodometric titrations and X-ray photoelectron spectroscopy. Electrical conductivity measurements in a wide range of temperatures revealed semiconducting behavior for all four materials. Electrocatalytic properties were studied for both half-reactions of water-splitting, namely, oxygen-evolution and hydrogen-evolution reactions (OER and HER). For the four materials, the trends in both OER and HER were the same, which also matched the trend in electrical conductivities. Among them, LaSrMn0.5Co0.5O4 showed the best bifunctional electrocatalytic activity for both OER and HER, which may be attributed to its higher electrical conductivity and favorable electron configuration.

Mn incorporated RuO2 nanocrystals as an efficient and stable bifunctional electrocatalyst for oxygen evolution reaction and hydrogen evolution reaction in acid and alkaline

The development of efficient and stable bifunctional overall water-splitting is a crucial goal for clean and renewable energy, which is a challenging task. Herein, we report an Mn-incorporated RuO2 (Mn-RuO2) catalyst for highly efficient electrocatalytic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in acid and alkaline media. Benefiting from a more electrochemical active area with the incorporation of Mn, the Mn-RuO2 required an overpotential of 200 mV to attain a current density of 10 mA/cm2 for OER in acid. DFT result indicates that the doping of Mn into RuO2 can enhance the OER activity. An acidic overall water-splitting electrolyzer with good stability constructed by bifunctional Mn-RuO2 only requires a cell voltage of 1.50 V to afford 10 mA/cm2 and can operate stably for 50 h at 50 mA/cm2, which is better than the state-of-the-art Ru-based catalyst. Additionally, the Mn-RuO2 exhibits excellent HER and OER activity in alkaline media, and it shows superior activity and durability for overall water-splitting, only needing a cell voltage of 1.49 V to attain 10 mA/cm2. The present work provides an efficient approach to designing and constructing efficient Ru-based electrocatalysts for overall water-splitting.