Oxygenate-induced structural evolution of high-entropy electrocatalysts for multifunctional alcohol electrooxidation integrated with hydrogen production.

High-entropy compounds have been emerging as promising candidates for electrolysis, yet their controllable electrosynthesis strategy remains a formidable challenge because of the ambiguous ionic interaction and codeposition mechanism. Herein, we report a oxygenates directionally induced electrodeposition strategy to construct high-entropy materials with amorphous features, on which the structural evolution from high-entropy phosphide to oxide is confirmed by introducing vanadate, thus realizing the simultaneous optimization of composition and structure. The representative P-CoNiMnWVOx shows excellent bifunctional catalytic performance toward alkaline hydrogen evolution reaction and ethanol oxidation reaction (EOR), with small potentials of -168 mV and 1.38 V at 100 mA cm-2, respectively. In situ spectroscopy illustrates that the electrochemical reconstruction of P-CoNiMnWVOx induces abundant Co-O species as the main catalytic active species for EOR and follows the conversion pathway of the C2 product. Theoretical calculations reveal the optimized electronic structure and adsorption free energy of reaction intermediates on P-CoNiMnWVOx, thereby resulting in a facilitated kinetic process. A membrane-free electrolyzer delivers both high Faradaic efficiencies of acetate and H2 over 95% and superior stability at100 mA cm-2 during 120 h electrolysis. In addition, the unique composition and structural advantages endow P-CoNiMnWVOx with multifunctional catalytic activity and realize multipathway electrosynthesis of formate-coupled hydrogen production.

Pt-decorated spinel MnCo2O4 nanosheets enable ampere-level hydrazine assisted water electrolysis.

Coupling hydrazine oxidation reaction (HzOR) with hydrogen evolution reaction (HER) has been widely concerned for high efficiency of green hydrogen preparation with low energy consumption. However, the lacking of bifunctional electrodes with ampere-level performance severely limits its industrialization. Herein, we put forward an efficient active site anchored strategy for MnCo2O4 nanosheet arrays on nickel foam (NF) by introducing Pt species (denoted as Pt-MnCo2O4/NF), which is standing for excellent bifunctional electrodes. The Pt-MnCo2O4/NF delivers ultralow potentials of -195 mV and 350 mV at 1000 mA cm-2 as well as robust stability for HzOR and HER, respectively. The study of in-situ Raman and reaction kinetics reveal that the formation of key adsorbed *NH2 and *N2H4 intermediates and the rapidly oxidization of intermediates with a fast interfacial charge transfer on Pt-MnCo2O4/NF. Remarkably, the Pt-MnCo2O4/NF assembled two-electrode hydrazine assisted water electrolyzer realizes current density of 100 mA cm-2 and 1000 mA cm-2 at 0.16 V and 0.62 V with over 80 h stability. This work provides a promising way to design efficient electrodes for energy-saving H2 generation under ampere-level current density.

Regulation Strategy of Nanostructured Engineering on Indium-Based Materials for Electrocatalytic Conversion of CO2.

Electrochemical carbon dioxide reduction (CO2 RR), as an emerging technology, can combine with sustainable energies to convert CO2 into high value-added products, providing an effective pathway to realize carbon neutrality. However, the high activation energy of CO2 , low mass transfer, and competitive hydrogen evolution reaction (HER) leads to the unsatisfied catalytic activity. Recently, Indium (In)-based materials have attracted significant attention in CO2 RR and a series of regulation strategies of nanostructured engineering are exploited to rationally design various advanced In-based electrocatalysts, which forces the necessary of a comprehensive and fundamental summary, but there is still a scarcity. Herein, this review provides a systematic discussion of the nanostructure engineering of In-based materials for the efficient electrocatalytic conversion of CO2 to fuels. These efficient regulation strategies including morphology, size, composition, defects, surface modification, interfacial structure, alloying, and single-atom structure, are summarized for exploring the internal relationship between the CO2 RR performance and the physicochemical properties of In-based catalysts. The correlation of electronic structure and adsorption behavior of reaction intermediates are highlighted to gain in-depth understanding of catalytic reaction kinetics for CO2 RR. Moreover, the challenges and opportunities of In-based materials are proposed, which is expected to inspire the development of other effective catalysts for CO2 RR.

Anion-modulated CoP electrode as bifunctional electrocatalyst for anion-exchange membrane hydrazine-assisted water electrolyser.

The hydrazine oxidation reaction (HzOR) is considered as a promising alternative process of the oxygen evolution reaction (OER) to realize more energy-efficient hydrogen generation. However, the lack of highly active bifunctional catalysts poses a huge challenge to this strategy. In this work, we report a novel and universal electrodeposition strategy to rationally synthesize a self-supporting electrode. The utilization of ammonium fluoride helps to modulate not only the morphology of CoP, but also the synchronous formation of an anion-modified structure, leading to an excellent bifunctional performance. The optimal F-CoP/CF exhibits small potentials of -90 mV and 41 mV at 1 A cm-2, high stability and low Tafel slopes of 28 mV dec-1 and 3.26 mV dec-1 for the HER and HzOR, respectively. The highly efficient and stable bifunctional activity of F-CoP/CF can be further confirmed in an anion-exchange membrane hydrazine-assisted water electrolyzer (0.49 V at 1 A cm-2). Utilizing the density functional theory calculations, the optimized adsorption energy of water molecules and hydrogen intermediates of the HER as well as the rate-determining step of the HzOR are demonstrated for the F-CoP.

Phosphorus-Modified Amorphous High-Entropy CoFeNiCrMn Compound as High-Performance Electrocatalyst for Hydrazine-Assisted Water Electrolysis.

Exploiting highly active and bifunctional catalysts for both hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR) is a prerequisite for the hydrogen acquisition. High-entropy materials have received widespread attention in catalysis, but the high-performance bifunctional electrodes are still lacking. Herein, a novel P-modified amorphous high-entropy CoFeNiCrMn compound is developed on nickel foam (NF) by one-step electrodeposition strategy. The achieved CoFeNiCrMnP/NF delivers remarkable HER and HzOR performance, where the overpotentials as low as 51 and 268 mV are realized at 100 mA cm-2 . The improved cell voltage of 91 mV is further demonstrated at 100 mA cm-2 by assessing CoFeNiCrMnP/NF in the constructed hydrazine-assisted water electrolyser, which is almost 1.54 V lower than the HER||OER system. Experimental results confirm the important role of each element in regulating the bifuncational performance of high-entropy catalysts. The main influencing elements seem to be Fe and Ni for HER, while the P-modification and Cr metal may contribute a lot for HzOR. These synergistic advantages help to lower the energy barriers and improve the reaction kinetics, resulting in the excellent bifunctional activity of the CoFeNiCrMnP/NF. The work offers a feasible strategy to develop self-supporting electrode with high-entropy materials for overall water splitting.

Rational Design of Molybdenum-Doped Cobalt Nitride Nanowire Arrays for Robust Overall Water Splitting.

Rational design of efficient electrocatalysts is highly imperative but still a challenge for overall water splitting. Herein, we construct self-supported Co3 N nanowire arrays with different Mo doping contents by hydrothermal and nitridation processes that serve as robust electrocatalysts for overall water splitting. The optimal Co3 N-Mo0.2 /Ni foam (NF) electrode delivers a low overpotential of 97 mV at a current density of 50 mA cm-2 as well as a highly stable hydrogen evolution reaction (HER). Density functional theory (DFT) calculations prove that Mo doping can effectively modulate the electronic structure and surface adsorption energies of H2 O and hydrogen intermediates on Co3 N, leading to improved reaction kinetics with high catalytic activity. Further modification with FeOOH species on the surface of Co3 N-Mo0.2 /NF improves the oxygen evolution reaction (OER) performance benefiting from the synergistic effect of dual Co-Fe catalytic centers. As a result, the Co3 N-Mo0.2 @FeOOH/NF catalysts display outstanding OER catalytic performance with a low overpotential of 250 mV at 50 1 mA cm-2 . The constructed Co3 N-Mo0.2 /NF||Co3 N-Mo0.2 @FeOOH/NF water electrolyzer exhibits a small voltage of 1.48 V to achieve a high current density of 50 mA cm-2 at 80 °C, which is superior to most of the reported electrocatalysts. This work provides a new approach to developing robust electrode materials for electrocatalytic water splitting.

Coupled MoO3-x@CoP heterostructure as a pH-universal electrode for hydrogen generation at a high current density.

Developing high-performance and low-cost self-supporting electrodes as pH-universal electrocatalysts for the hydrogen-evolution reaction (HER) and realizing high-quality hydrogen production at a high current density are highly desirable, but are hugely challenging. We created a self-supporting electrode with a coupled hierarchical heterostructure by simple electrodeposition followed by sulfurization. It comprised oxygen-deficient molybdenum oxide (MoO3-x) and cobalt phosphide (CoP) on nickel foam (NF), which represented a highly active pH-universal electrocatalyst for the HER at a high current density. Benefiting from a plethora of catalytic active sites, improved interfacial charge transfer, and strong electronic interaction, this type of MoO3-x@CoP/NF electrode delivered a superior catalytic performance. Overpotentials of only 100 mV, 135 mV, and 400 mV were needed to realize a high current density of 1 A cm-2 in alkaline, acid and neutral media, respectively, which were superior to those of most other well-developed materials based on non-noble metals. Our experimental work demonstrates the synergistic advantages of a MoO3-x@CoP heterostructure for improving the intrinsic catalytic performance but also paves a new path for the rational design of advanced electrodes for hydrogen generation in a wide range of pH conditions.

Engineering cobalt molybdate nanosheet arrays with phosphorus-modified nickel as heterogeneous electrodes for highly-active energy-saving water splitting.

Electrochemical urea electrolysis has been regarded as a promising strategy to replace traditional water-splitting technology to achieve hydrogen fuel due to its cost savings and high energy efficiency. Designing efficient bifunctional electrocatalysts easily is important but still faces significant challenges. Herein, an interface engineering strategy is used to construct a hybrid material by coupling cobalt molybdate (CoMoO4) nanosheet arrays with phosphorus-modified nickel (P-Ni) particles on copper foam (P-Ni@CoMoO4/CF) through the hydrothermal and in-situ electrodeposition process. Benefiting from the abundant catalytic active sites, low charge transfer resistance, and synergistic coupling effect, the optimal P-Ni@CoMoO4/CF electrocatalyst presents a superior bifunctional activity for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER). In detail, a small overpotential of 125 mV and a low potential of 1.36 V is required to attain the current density of 100 mA cm-2 for HER and UOR, respectively. In the process of urea electrolysis, the P-Ni@CoMoO4/CF-based electrolyzer provides a current density of 100 mA cm-2 with an overall voltage of 1.50 V, about 170 mV less than that in a traditional water electrolyzer. The high performance of P-Ni@CoMoO4/CF outperforms many recently reported electrodes, suggesting its promising application in energy-saving hydrogen production. Our work proposes a novel idea for the rational design and exploitation of low-cost and robust bifunctional electrodes for electrocatalysis.

Engineering Coupled NiSx -WO2.9 Heterostructure as pH-Universal Electrocatalyst for Hydrogen Evolution Reaction.

Exploiting highly active and low-cost materials as pH-universal electrocatalysts for the hydrogen evolution reaction (HER) and achieving high-purity hydrogen fuel is highly desirable but remains challenging. Herein, a novel type of coupled heterostructure was designed by simple electrodeposition followed by a sulfurization treatment. This hierarchical structure was composed of nickel sulfides (NiS, NiS2 , denoted as NiSx ) and oxygen-deficient tungsten oxide (WO2.9 ), which was directly grown on nickel foam (NF) as self-supporting electrodes (NiSx -WO2.9 /NF) for HER over a wide pH range. The systematic experimental characterizations confirmed that the material had abundant catalytic active sites, fast interfacial electron transfer ability, and strong electronic interaction, resulting in the optimized reaction kinetics for HER. Consequently, the NiSx -WO2.9 /NF catalyst required low overpotentials of 96 and 117 mV to reach current densities of 50 and 100 mA cm-2 in an alkaline medium, outperforming most of the reported non-noble metal-based materials. Moreover, this self-supported electrode exhibited impressive performance over a wide pH range, only requiring 220 and 304 mV overpotential at 100 mA cm-2 in 0.5 m H2 SO4 and 1 m phosphate-buffered saline electrolytes. This work may offer a new approach to the development of advanced pH-universal electrodes for hydrogen production.

Universal strategy of iron/cobalt-based materials for boosted electrocatalytic activity of water oxidation.

Low-dimensional cobalt-based materials have proved to be one of the promising catalytic systems for oxygen-evolution reaction (OER). How to develop a facile and universal strategy for significantly improving their catalytic performance is of great significance, but still faces great challenges. Herein, a series of cobalt-based nanowires (CoS2, CoP, CoF2, and Co3O4) are synthesized and used as conceptual examples to explore the universality to enhance their OER catalytic activity. The FeOOH-modified cobalt-based electrocatalysts exhibit significantly improved OER catalytic performance compared to the pristine samples. Especially, the optimal CoS2@FeOOH material delivers the smallest overpotential of 260 mV at 100 mA cm-2, which outperforms most of the reported excellent materials. Notably, the CoP||CoP@FeOOH electrolyzer (1.63 V@30 mA cm-2) delivers higher performance than the CoS2||CoS2@FeOOH electrolyzer (1.72 V@30 mA cm-2) benefiting from the better HER catalytic activity of CoP. In addition, the post-characterizations confirm that the real catalytic structure of those electrocatalysts consists of a surface CoOOH@FeOOH catalytic layer and cobalt-based nanowire core. The Co-Fe catalytic layer provides more active centers for the adsorption and dissociation of water molecules as well as the formation of oxygen, while the nanowire core acts as an electron transport channel to realize better reaction kinetics. Our work not only develops a general strategy to enhance the catalytic activity but also provides new ideas for the facile design of other advanced catalytic materials.

Hierarchically structured nickel/molybdenum nitride heterojunctions as superior bifunctional electrodes for overall water splitting.

Transition metal nitrides (TMNs) are considered to be some of the most promising metallic materials for electrocatalytic water splitting. However, the low density of active sites and weak reaction kinetics still limit their wide industrial application. Herein, we put forward a typical 3D hierarchical heterostructure that is composed of metallic Ni3N, Mo5N6, and Ni grown on nickel foam (denoted as Ni3N@NiMoNx/NF), presenting it as a highly-active bifunctional electrocatalyst for water splitting. This hybrid nanowire heterojunction has an abundant interface structure for more catalytically active sites, while its synergistic effects of strong electronic interaction and intrinsic high conductivity ensure fast electron transfer for rapid reaction kinetics. Remarkably, the Ni3N@NiMoNx/NF electrode delivers small overpotentials of 78 mV and 370 mV at 100 mA cm-2 for the HER and OER, respectively. By utilizing Ni3N@NiMoNx/NF as bifunctional electrodes for water splitting, an alkaline electrolyzer shows a low cell voltage of 1.68 V at 100 mA cm-2 with a superior durability of 80 h. Our work provides an experimental basis for advancing the rational design of efficient and stable bifunctional electrocatalysts for large-scale industrial water electrolysis applications.

Heterostructure engineering of iridium species on nickel/molybdenum nitride for highly-efficient anion exchange membrane water electrolyzer.

Developing highly active electrocatalysts is a pivotal issue for anion-exchange membrane water electrolyzers (AEMWE). However, realizing the continuous hydrogen generation at a large current density remains challenging. Herein, a novel kind of hybrid electrode is successfully developed by introducing trace iridium (Ir) species onto a hierarchical Ni/Mo5N6 heterostructure on Ni foam (Ir-Ni/Mo5N6/NF). The synergistic advantages of high conductivity, abundant active sites, and strong electronic interaction endow superior reaction kinetics, presenting a highly-active bifunctional electrocatalyst. Remarkably, the Ir-Ni/Mo5N6/NF exhibit extremely low overpotentials of 52 mV and 250 mV at 100 mA cm-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). By exploiting the Ir-Ni/Mo5N6 as both anode/cathode, the constructed AEMWE device delivers superior performance. The current density reaches 2.1 A cm-2 at a voltage of 2.0 V and 250 mA cm-2 at 1.8 V in alkaline/neutral media. This work put forward a facile and effective strategy to synthesize advanced bifunctional electrocatalysts for water electrolysis.

Fluorine-anion engineering endows superior bifunctional activity of nickel sulfide/phosphide heterostructure for overall water splitting.

Designing advanced transition metal-based materials for electrocatalytic water splitting is of significance, but their wide application is still limited due to the lack of an effective regulation strategy. Herein, a synergistic regulation strategy of surface/interface is developed to optimize the catalytic activity of nickel sulfide (Ni3S2). The construction of nickel phosphide with Ni3S2 heterostructure by using fluorine (F)-anion modification is successfully developed on nickel foam (F-NiPx/Ni3S2-NF) via a simple fluorination and phosphating treatment. This new kind of electrocatalyst contains plenty of active sites and strong electronic interactions, presenting superior bifunctional activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The overpotentials only need 182 mV and 370 mV to reach the current density of 100 mA cm-2 for HER and OER, respectively. In addition, the F-NiPx/Ni3S2-NF-based electrolyzer delivers promising performance for overall water splitting. A low potential of 1.55 V and 1.7 V can be achieved at the current density of 10 mA cm-2 and 50 mA cm-2. This work provides a new surface/interface regulation strategy for high-efficient bifunctional electrocatalysts.

Electronic regulation of platinum species on metal nitrides realizes superior mass activity for hydrogen production.

Developing high-active electrocatalyst to improve the efficiency of hydrogen evolution reaction (HER) is critical to achieve clean hydrogen. However, the low mass activity and high cost of this technology still limits its wide commercial application. Herein, a new kind of hybrid material is designed by introducing trace Pt species onto a mixed metal nitride matrixs (denoted as NiWNx), presenting as an excellent electrocatalyst for HER. The prepared Pt-NiWNx hybrid possesses abundant heterointerfaces, high conductivity and strong electron interactions, facilitating the reaction kinetics for hydrogen production. As a result, the Pt-NiWNx only needs a small overpotential of 61 mV to reach the geometric current density of 100 mA cm-2 in alkaline electrolyte. Notably, this kind of catalyst delivers a superior mass activity of 32.8 A mgPt-1 at -0.1 V and high durability, exhibiting the promising prospects for industrial application. This work offers a novel design strategy for high-efficient hybrid materials for scaled hydrogen generation.

Highly efficient electrochemical reduction of carbon dioxide to formate on Sn modified Bi2O3 heterostructure.

In this work, Sn species are deposited onto the surface of a Bi2O3 material by a facile disproportionated reaction and the prepared catalyst shows a superior electrocatalytic performance towards CO2 reduction. The deposition of Sn atoms can donate electrons to the Bi2O3 material and increase its electrical conductivity. The SnM-Bi2O3 catalyst with the optimal Sn content delivers a high faradaic efficiency of 95.8% at -1.0 V for formate production. In addition, the partial current density of formate can reach 41.8 mA cm-2. The SnM-Bi2O3 catalyst also exhibits superior stability towards long-term electrolysis. The modification of Sn species not only helps to stabilize the reaction intermediate but also inhibits the hydrogen evolution reaction (HER) pathway, achieving the synergetic enhancement of catalytic activity.

Optimized hierarchical nickel sulfide as a highly active bifunctional catalyst for overall water splitting.

Rational design of non-noble metal electrocatalysts with high intrinsic activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is extremely impressive for sustainable electrocatalytic water splitting systems. However, it still remains a major challenge to engineer bifunctional performance. Here, we put forward a highly efficient water electrolyzer based on Ni3S2-based materials. The hierarchical structure of Ni3S2 can be well regulated for optimizing the HER catalytic activity. The best c-Ni3S2/NF electrode exhibits a much smaller overpotential of 220 mV to reach the current density of 100 mA cm-2. Upon introducing Fe species onto the Ni3S2/NF electrode by a simple dipping/drying method, the intrinsic OER activity can be extremely improved. As a result, the Fe-c-Ni3S2/NF catalyst showed excellent catalytic activity for the OER, including an overpotential of 193 mV at 10 mA cm-2, high specific current density and excellent stability. Post-characterization studies proved that the remaining S anions have an effective influence on improving the OER intrinsic activity. The assembled water electrolyzer also presented superior performance, such as a very low cell voltage of 1.50 V at 10 mA cm-2 and excellent durability for 120 h in alkaline medium. This strategy provides a promising way to design highly active and low-cost materials for overall water electrolysis.

Cobalt phosphide nanowires with adjustable iridium, realizing excellent bifunctional activity for acidic water splitting.

The exploration of highly active bifunctional electrocatalysts for acidic electrochemical water splitting has attracted wide attention due to their importance in polymer electrolyte membrane (PEM) electrolyzers. However, existing catalysts normally suffer from low catalytic efficiency under acidic conditions. Herein, we developed a series of Ir-doped CoP nanowires arrays on carbon cloth (Ir-CoP/CC) materials, realizing prominently improved bifunctional catalytic activity for overall water splitting in an acidic medium. The optimized Ir4-CoP/CC catalyst exhibits the smallest overpotential of 38 mV and 237 mV to reach 10 mA cm-2 for HER and OER, respectively. Through systematic experimental research, we find the best intrinsic activity belongs to Ir3-CoP/CC catalyst, which presents superior bifunctional performance with the most economical usage of Ir. As a result, the best acidic water splitting electrolyzer displays a very low voltage of 1.50 V at 10 mA cm-2. This work provides a novel strategy to develop highly active bifunctional catalysts for acidic electrochemical water splitting.

Dual Vacancies Confined in Nickel Phosphosulfide Nanosheets Enabling Robust Overall Water Splitting.

Exploring highly efficient electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is of great significance for addressing energy and environmental crises. Vacancy engineering has been regarded as a promising way to optimize the catalytic activity of electrocatalysts. Herein, we put forward a conceptually new dual Ni,S vacancy engineering on 2D NiPS3 nanosheet (denoted as V-NiPS3 ) by a simple ball-milling treatment with ultrasonication. This material presents an ideal model for exploring the role of dual vacancies in improving the catalytic activity for overall water splitting. Structural analyses make clear that the formation of dual Ni,S vacancies regulates the electronic structure and catalytic active sites of NiPS3 nanosheet, leading to the superior HER/OER performance. Smaller overpotentials of 124 mV and 290 mV can be achieved at a current density of 10 mA cm-2 for HER and OER, respectively. The OER performance of V-NiPS3 is the best value among all state-of-the-art NiPS3 catalysts. In addition, the assembled two-electrode cell incorporating V-NiPS3 exhibits enhanced catalytic performance with a low cell voltage of 1.60 V at 10 mA cm-2 . This work offers a promising avenue to improve the electrocatalytic performance of the catalysts by engineering dual vacancies for large-scale water splitting.

Dual anions engineering on nickel cobalt-based catalyst for optimal hydrogen evolution electrocatalysis.

The hydrogen evolution reaction (HER) is a pivotal process for renewable energy storage devices. Improving the intrinsically catalytic activity of earth-abundant metals based electrocatalysts for HER is still a huge challenge. Herein, we put forward a dual phosphorus/sulfur (P/S) doped nickel-cobalt bimetallic material that was grown on nickel foam (Sn-NiCoPx-NF, n = 1-4, NF stands for nickel foam) through a facile one-step phosphorization/sulfuration reaction. Those catalysts represent a novel kind of electrocatalysts with vastly optimized catalytic activity for HER. The S2-NiCoPx/NF with optimal P/S ratio achieves unexpectedly highly efficient catalytic activity for HER in alkaline medium. The overpotential at the current density of 50 mA cm-2 is only 144 mV, which is almost 190 mV less than that of pristine nickel-cobalt bimetallic phosphide catalyst (NiCoPx-NF). In addition, the S2-NiCoPx/NF also has fast reaction kinetics with the smallest Tafel slope of 66 mV/dec and exhibits high stability for HER. This work experimentally demonstrates the advantages of a dual anion modification strategy on improving catalytic activity. Our method offers a new approach to design highly efficient and low-cost electrocatalysts for energy storage and conversion devices.

Nitrogen-Incorporated Cobalt Sulfide/Graphene Hybrid Catalysts for Overall Water Splitting.

Water electrolysis is an advanced and sustainable energy conversion technology used to generate H2 . However, the low efficiency of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) hampers the overall water-splitting catalytic performance. Here, a hybrid catalyst was constructed from N-doped CoS2 nanoparticles on N,S-co-doped graphene nanosheets (N-CoS2 /G) using a facile method, and the catalyst exhibited excellent bifunctional activity. Introduction of N atoms not only promoted the adsorption of reaction intermediates, but also bridged the CoS2 nanoparticles and graphene to improve electron transfer. Moreover, using thiourea as both N- and S-source ensured synthesis of much smaller-sized nanoparticles with more surface active sites. Surprisingly, the N-CoS2 /G exhibited superior catalytic activity with a low overpotential of 260 mV for the OER and 109 mV for the HER at a current density of 10 mA cm-2 . The assembled N-CoS2 /G : N-CoS2 /G electrolyzer substantially expedited overall water splitting with a voltage requirement of 1.58 V to reach 10 mA cm-2 , which is superior to most reported Co-based bifunctional catalysts and other non-precious-metal catalysts. This work provides a new strategy towards advanced bifunctional catalysts for water electrolysis.