Hydrothermally/electrochemically decorated FeSe on Ni-foam electrode: An efficient bifunctional electrocatalysts for overall water splitting in an alkaline medium

A new hybrid catalyst based on Ni foam (NF) and FeSe was prepared by a facial hydrothermal method, in which Se-decorated NF was subsequently electrochemically doped by Fe. Binder-free catalyst containing electrodes were directly tested for the hydrogen and oxygen evolution reaction (HER/OER). The FeSe/NF electrode displayed an OER current density of 100 mA cm⁻² at potential of 1.42 V, and a relatively small Tafel slope of 109 mV dec⁻¹ in a 1 M KOH solution. Also, FeSe/NF electrode exhibited reasonable HER overpotential of 200 mV at 10 mAcm⁻² current density with Tafel slope of 145 mV dec⁻¹. The XRD and TEM studies revealed that the formation of heterogeneous interfaces of NiSe₂ and FeSe₂,generated more active sites that can promote better ions and electron transport in the electrode/electrolyte interfaces. Furthermore, HRTEM analysis indicates that FeSe₂ rich in Se vacancy defects can be created with suitable M − O and M − H bond for better OER and HER performance, respectively. In a-two electrode alkaline water electrolyzer, current densities of 10 mA cm⁻² and 50 mA cm⁻² were obtained at cell voltages of 1.52 V and 1.85 V, respectively, using pure FeSe–NF as both the cathode and anode.     

Facile synthesis of copper selenide with fluffy intersected-nanosheets decorating nanotubes structure for efficient oxygen evolution reaction

Rational nanostructure design is the key point to prepare catalysts with superior catalytic performance, and tedious preparation method limits them large-scale application. Here, a Cu₂Se with fluffy intersected-nanosheets decorating nanotubes structure were prepared by a simple and rapid solution-immersion method at room temperature. The hollow hierarchical structure on a good conductor Cu foam (CF) enlarges surface available sites, enhances the conductivity of electrode materials, then endowing the catalyst with quick charge/mass transportation and favorable oxygen evolution reaction (OER) performance. In alkaline medium, our as-prepared Cu₂Se/CF electrode demonstrates high OER performance, especially for lower overpotential (200 mV at 10 mA cm⁻²) compared with the previously reported Cu-based catalysts. Moreover, the Cu₂Se catalyst could afford galvanostatic test of 10 mA cm⁻² test over 12 h and present superior OER tolerance. These results indicate that the Cu₂Se catalyst via cost efficiency and efficient solution-immersion method could be applied to large-scale efficient OER.     

Surface engineering of 2D MOF to construct high-density Co9S8 nanoparticles supported on nitrogen doped carbon for efficient oxygen evolution reaction

Transition metal sulfides and their hybrids are promising alternative to precious metal catalyst for the oxygen evolution reaction (OER). Herein, the high-density Co₉S₈ nanoparticles (NPs) embedded in N-doped carbon has been prepared by using surface-engineered zeolitic imidazolate framework-9 (ZIF-9) nanosheets as precursor. The surface of ZIF-9 was modified with TAA, which is able to create chemical barrier and prevents metal from aggregation in the subsequent pyrolysis, thus making small Co₉S₈ NPs densely anchored on carbon layers. Arising from the unique structure, Co₉S₈@NC affords an optimized electronic structure and rich effective reactive sites for OER. As expected, Co₉S₈@NC exhibits small overpotential of 264 mV at 10 mA cm⁻², low Tafel slope of 68.4 mV dec⁻¹, and superior stability for alkaline OER (0.1 M KOH). The electrolysis cell, which was equipped with Co₉S₈@NC cathode and Pt/C anode, shows low water splitting voltage of 1.58 V at 10 mA cm⁻² in 1.0 M KOH. This work employs an efficacious surface engineering strategy to design metal sulfide-based electrocatalysts for enhancing OER performance.     

Flower-like Co3O4 microstrips embedded in Co foam as a binder-free electrocatalyst for oxygen evolution reaction

Designing appropriate oxygen evolution reaction (OER) electrocatalysts to meet the requirements of high efficiency, long-term durability, and low cost remains the challenge for scientific community. Cobalt oxide (Co₃O₄) has been proven as a promising candidate for OER with attractive activity and stability in alkaline media. In this study, flower-like Co₃O₄ microstrips have been successfully prepared and directly embedded in Co foam (denoted as Co₃O₄@Co foam) by a green and facile two-step strategy including hydrothermal treatment and subsequent annealing process under relatively low temperatures. It demonstrates that the OER performance of the Co₃O₄@Co foam electrode can rival to the commercial RuO₂ on glassy carbon electrode. The Co₃O₄@Co foam electrode displays high OER activity with a low overpotential of 273 mV at a current density of 10 mA cm⁻², and a low Tafel slope of 61.8 mV dec⁻¹. The flower-like Co₃O₄ microstrips greatly increase the active surface area to expose more active sites, and the directly growth of Co₃O₄ microstrips on Co foam with intimate contact improves the electron transport and ensures the stability of the Co₃O₄@Co foam electrode.     

Embedding Co2P nanoparticles into co-doped carbon hollow polyhedron as a bifunctional electrocatalyst for efficient overall water splitting

The reasonable design and construction of non-precious metal electrocatalysts with low cost and high performance is critical for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, a facile polymerization-pyrolysis method is proposed to encapsulate Co₂P nanoparticles in co-doped hollow carbon shell by using ZIF-67 and P-containing polymers as precursor. The unique construction not only effectively prevents nanoparticles from detaching, showing good stability after long-term testing, but also provides abundant active sites, large surface areas and large pore volumes, enabling the electrolyte and electrode material to full contact. As expected, the Co₂P/NPSC-800 performs superior HER performance with low overpotential of 173 mV at 10 mA cm⁻² and excellent stability of 88% retention for 35 h and OER performance with low overpotential of 320 mV at 10 mA cm⁻², which endows Co₂P/NPSC-800 with good catalytic activity in overall water splitting. Furthermore, density functional theory (DFT) calculations reveal that the metallic property and the decreased reaction barriers of Co₂P can promote the catalytic reactions. This work offers an effective route in synthesizing other transition metal phosphides with high catalytic properties.     

One-pot solvothermal synthesis of Co2P nanoparticles: An efficient HER and OER electrocatalysts

Development of an inexpensive electrocatalyst for hydrogen evolution (HER) and oxygen evolution reactions (OER) receives much traction recently. Herein, we report a facile one-pot ethyleneglycol (EG) mediated solvothermal synthesis of orthorhombic Co₂P with particle size ~20–30 nm as an efficient HER and OER catalysts. Synthesis parameters like various solvents, temperatures, precursors ratios, and reaction time influences the formation of phase pure Co₂P. Investigation of Co₂P as an electrocatalyst for HER in acidic (0.5 M H₂SO₄) and alkaline medium (1.0 M KOH), furnishes low overpotential of 178 mV and 190 mV, respectively to achieve a 10 mA cm^?2 current density with a long term stability and durability. As an OER catalyst in 1.0 M KOH, Co₂P shows an overpotential of 364 mV at 10 mA cm^?2 current density. Investigation of Co₂P NP by XPS analysis after OER stability test under alkaline medium confirms the formation of amorphous cobalt oxyhydroxide (CoOOH) as an intermediate during OER process.     

Ir-doped Co3O4 as efficient electrocatalyst for acidic oxygen evolution reaction

Oxygen evolution reaction (OER) is an important bottleneck for large-scale acidic water splitting applications due to its sluggish reaction kinetics. Therefore, the development of highly active, stable, and inexpensive electrocatalysts for OER remains a challenge. Herein, we develop the iridium doped Co₃O₄ (Ir–Co₃O₄) with low Ir content of 2.88 wt% for efficient acidic OER. Considering systemic characterizations, it is probably concluded that Ir can be uniformly doped into the lattice of Co₃O₄ and induce a certain distortion. The electrochemical results reveal that Ir–Co₃O₄ nanoparticles demonstrate significantly enhanced electrocatalytic OER activity and stability in 0.5 M H₂SO₄ solution compared with pure Co₃O₄, in which the overpotential at the current density of 10 mA cm⁻² decreases from 382 mV to 225 mV and the value of Tafel slope decreases from 101.7 mV dec⁻¹ to 64.1 mV dec⁻¹. Besides, Ir–Co₃O₄ exhibits excellent electrocatalytic durability for continuous 130 h's test without any activity attenuation. Moreover, this work provides a kind of high-performance acidic OER electrocatalyst for the development of hydrogen energy.     

Multi-shelled CoS2–MoS2 hollow spheres as efficient bifunctional electrocatalysts for overall water splitting

The exploration of highly efficient non-precious electrocatalysts is essential for water splitting devices. Herein, we synthesized CoS₂–MoS₂ multi-shelled hollow spheres (MSHSs) as efficient electrocatalysts both for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) using a Schiff base coordination polymer (CP). Co-CP solid spheres were converted to Co₃O₄ MSHSs by sintering in air. CoS₂–MoS₂ MSHSs were obtained by a solvothermal reaction of Co₃O₄ MSHSs and MoS₄²⁻ anions. CoS₂–MoS₂ MSHSs have a high specific surface area of 73.5 m²g^-1. Due to the synergistic effect between the CoS₂ and MoS₂, the electrode of CoS₂–MoS₂ MSHSs shows low overpotential of 109 mV with Tafel slope of 52.0 mV dec⁻¹ for HER, as well as a low overpotential of 288 mV with Tafel slope of 62.1 mV dec⁻¹ for OER at a current density of 10 mA cm⁻² in alkaline solution. The corresponding two-electrode system needs a potential of 1.61 V (vs. RHE) to obtain anodic current density of 10 mA cm⁻² for OER and maintains excellent stability for 10 h.     

SrTi0.1CoxFe0.9-xO3-δ Perovskites for enhanced oxygen evolution reaction activity

We developed a series of Fe doping in Co-based perovskites SrTi_0.1Co_xFe_0.9-xO_3-δ (x = 0.5, 0.6, 0.7, 0.9) to investigate their OER activity and stability in alkaline media. Among all the samples, SrTi_0·1Co_0·5Fe_0·4O_3-δ (donated as STCF-154) shows wonderful OER activity with an overpotential of 0.37 V, a current density of 33.65 mA cm⁻² at 1.71 V, and a Tafel slope of 94.82 mV dec⁻¹. Besides, the potential of STCF-154 remained nearly unchanged for at least 8 h at a fixed current density of 10 mA cm⁻²_disk on GC electrode. The improved activity and stability are likely originating from the highly oxidative oxygen species O₂²⁻/O⁻ formed in STCf-154, which can easily migrate from bulk STCF-154 and “spillover” to the surface of the catalyst during OER process. The Fe doping in Co-based perovskites had synergetically enhanced activity and can be considered as a good candidate for the OER in alkaline solution.     

Bundle-shaped cobalt–nickel selenides as advanced electrocatalysts for water oxidation

Searching for high-performance and earth-abundant electrocatalysts for oxygen evolution reaction (OER) is of paramount significance for overall water splitting to produce hydrogen. Herein, an advanced class of CoNi selenides containing rich oxygen vacancies, with a hierarchical bundle-like and holey nanosheets as noble-metal-free catalysts were first synthesized through a facile hydrothermal method. Benefitting from abundant oxygen vacancies, bundle-like nanostructure, as well as strong synergistic effects, such CoNi selenides demonstrate a greatly enhanced surface area to supply more electrocatalytic active sites to contact with electrolyte, accompanied by largely promoted reaction kinetics, which show outstanding electrocatalytic performances for OER. Remarkably, the optimal Co₁N_i0.5Se can display outstanding OER activity with the small Tafel slope of 48 mV dec⁻¹ and low overpotential of 250 mV (at 10 mA cm⁻²), which are much superior to those of Co/Ni-based catalysts. This electrocatalyst can also maintain high activity and structure stability during long-term electrolysis of 35 h, demonstrating a desirable electrocatalyst for OER. This work elucidates the sophisticated construction of well-defined non-noble metal catalysts for the practical applications in water oxidation.     

Se-doped cobalt oxide nanoparticle as highly-efficient electrocatalyst for oxygen evolution reaction

Electrolysis of water has been one of the most promising approaches for renewable energy resources while the efficient oxygen evolution reaction (OER) remains challenging. Herein, a series of different ratio of Se doped Co₃O₄ nanoparticles XSe-Co₃O₄ are prepared by hydrothermal method and applied as OER electrocatalysts. Se^2? is doped into the Co₃O₄ crystal lattice by substituting of O^2? and a large number of oxygen vacancies are generated, which provides more available activity sites for OER. Se doping increases the surface ratio of Co²⁺/Co³⁺ and accelerates the electron transport that favors OER activity promotion. The optimized doping ratio of 6%Se–Co₃O₄ presents low overpotential of 281 mV at 10 mA cm^?2, as well as a low Tafel slope of 70 mV dec^?1 in 1 M KOH solution, which has great advantages compared to the recently reported Co₃O₄-based OER electrocatalysts. This work provides new ideas for the development of efficient Co₃O₄-based OER electrocatalysts.     

Phytic acid-derived Co2-xNixP2O7-C/RGO and its superior OER electrocatalytic performance

A phytic acid-derived Co_2-xNi_xP₂O₇-C/RGO composite was designed and facilely synthesized, in which phytic acid acted as both a phosphoric source and carbon source. Both carbon derived from phytic acid and reduced graphene oxide (RGO) in composite, enhanced the conductivity and thus improve its electrocatalytical capability. As-synthesized Co_1.22Ni_0.78P₂O₇-C/RGO composite exhibited excellent oxygen evolution reaction (OER) catalytic performances: At the current density of 10 mA cm⁻², only a low overpotential of 283 mV and a small Tafel slope of 51 mV dec⁻¹ were observed. Good OER catalytic performance was retained even after 10 h continuously running at a constant voltage, which is even comparable to those of first-rate noble metal catalyst RuO₂. In addition, the performances of Co_2-xNi_xP₂O₇-C/RGO catalysts were also strongly dependent on Ni content.     

Green synthesis of CuCo2O4–CuO composite nanoparticles grown on nickel foam for high-performance oxygen evolution reaction

Among the most critical components for water-derived hydrogen fuel, the study of electrocatalysts as anode for the oxygen evolution reaction (OER) is an important topic in the water splitting process. In this work, the CuCo₂O₄–CuO composite electrode is synthesized directly on nickel foam to evaluate its potential as OER catalyst in an alkaline medium. An interesting strategy is to use flaxseed oil as a polymerizing agent in a sol-gel process combined with hydrothermal. A low overpotential value of 289 mV vs RHE at 10 mA cm⁻² current density and a Tafel slope of 71 mV dec⁻¹ were observed, which represents an electrocatalytic performance superior to other Cu and Co based oxides in the literature. Short-term stability testing of 15 h demonstrates stable overpotential with no observable secondary phase after measurements. The successful outcome of this work is a result of the promising green chemical approach herein used to obtain electrocatalysts grown directly on conductive substrates for water oxidation.     

An alkaline-acid asymmetric electrolyzer using NiCoP/CoP/Co3O4 multi-shell hollow nanoflakes as cathode and Ag as anode to realizing energy efficient production of hydrogen and shape controllable silver oxide

Large scale hydrogen generation by water electrolysis is severely impeded by the high cost of noble metal electrode materials and the kinetic-sluggish anodic oxygen evolution reaction (OER). Here we design a MOF-derived NiCoP/CoP/Co₃O₄ multi-shell hollow nanoflakes as a low-cost cathode electrocatalyst for hydrogen evolution reaction (HER), and replace the OER with more favorable silver oxidation reaction (AOR). The NiCoP/CoP/Co₃O₄ supported on carbon cloth (CC@NiCoP/CoP/Co₃O₄) endows an impressive low overpotential (η) of 90 mV at 10 mA cm⁻² and a low Tafel slope of 81.7 mV dec⁻¹ for HER in 0.5 M H₂SO₄ electrolyte. Coupling it with Ag electrode to forming an asymmetric alkali-acid electrolyzer exhibits superior performance with the requirement of a cell voltage of only 1.16 V to attain 10 mA cm⁻² with nearly 100% of Faradaic efficiencies for both H₂ and Ag₂O generation, showing dramatically lower voltage than that previously reported for conventional water splitting systems. In addition, the size and shape of Ag₂O can be controlled by manipulating current density. Our electrolyzer design provides not only an economical approach to produce H₂ and Ag₂O but also shows great promise for expansion into the electrosynthesis of other value-added chemicals.     

Novel 13X Zeolite/PANI electrocatalyst for hydrogen and oxygen evolution reaction

In this work, first 13X zeolite was prepared by the hydrothermal method. Then, the composite electrode was fabricated by using 13X zeolite and aniline monomer in nickel foam by electropolymerization technique in an acidic medium (13X/PANI). The synthesized 13X zeolite was characterized by physicochemical characterization techniques such as Fourier transform infra-red (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) pattern and nitrogen sorption isotherm. 13X/PANI composite was further analyzed by XRD, XPS and FE-SEM techniques. Furthermore, the catalyst activity of the synthesized 13X, PANI and 13X/PANI composite electrodes was evaluated in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) by using linear square voltammetry (LSV) and Tafel slope method. The Tafel slopes of HER were found to be 203 mV dec⁻¹, 440 mV dec⁻¹ and 282 mV dec⁻¹ for 13X, PANI and 13X/PANI-15 electrodes respectively. While the OER Tafel slopes were found to be 423 mV dec⁻¹, 310 mV dec⁻¹ and 168 mV dec⁻¹ for 13X, PANI and 13X/PANI-15, respectively. 13X/PANI-15 electrodes show excellent catalytic performance about the overpotential at 10 mA cm⁻² for HER and the overpotential at 20 mA cm⁻² for OER. The obtained results suggest fabricated novel electrodes are a potential candidate for HER and OER reaction and can be open new avenue for other electrochemical reactions.     

A novel efficient dual-functional electrocatalyst for overall water splitting based on Ni0.85Se/RGO/CNTs nanocomposite synthesized via different nickel precursors

Synthesizing efficient and affordable electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) remains a crucial problem on the way to practical applications for producing clean H₂ fuel. Herein, high-efficiency and stable transition metal based electrocatalysts Ni_0.85Se-1, Ni_0.85Se-2 and Ni_0.85Se-3 materials with different morphological characteristics were derived via a one-step hydrothermal route using the Ni(OH)₂ and metal-organic framework (Ni-BDC and Ni-BTC) as precursors, respectively. The results showed that Ni_0.85Se-2 exhibited excellent electrocatalytic activity. Subsequently, introducing carbon nanomaterials (RGO and CNTs) to form Ni_0.85Se/RGO/CNTs nanocomposite material further improves the catalytic activity owing to high conductivity. The resulting Ni_0.85Se/RGO/CNTs nanocomposites electrocatalyst showed a low overpotential of 232 mV and 165 mV and a low Tafel slope of 64 mV dec^?1 and 98 mV dec^?1 when the current density was 10 mA cm^?2 for OER and HER, respectively. In addition, the Ni_0.85Se/RGO/CNTs nanocomposites were used as an anode and cathode of the water electrolysis device and the overall water splitting performance was investigated. The results show just a voltage of 1.59 V was required when the current density was 10 mA cm^?2 and good overall water splitting stability for 20 h. The outstanding electrocatalytic performance of Ni_0.85Se/RGO/CNTs is mostly due to its noticeable porous structure, the high conductivity and the large surface area that came from RGO and CNTs.     

Modification of stainless steel fiber felt via in situ self-growth by electrochemical induction as a robust catalysis electrode for oxygen evolution reaction

The development of cost-effective, highly efficient and robust electrodes for oxygen evolution reaction (OER) is greatly significant for water-electrolysis to produce hydrogen. In this paper, we report a stainless steel fiber felt (SSF) electrode with greatly enhanced OER catalytic performance and durability. The SSF is directly treated by cyclic voltammetry (CV) method in alkaline electrolyte, which is more facile and convenient than the traditional measures. The characterization results of X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy indicate that an ultra-thin layer composed of Fe/Ni/Cr hydroxides/oxides with 3D open nanoporous structure is formed on the surface of SSF after CV treatment. The electrochemical tests show that the prepared SSF electrode displays a very low overpotential of 230 mV at 10 mA cm⁻², a small Tafel slope of 44 mV dec⁻¹ and good long-term durability of 550 h in 1 M KOH. The excellent OER performance of SSF electrode is contributed to the formation of hybrid metal hydroxides/oxides on its surface via in situ self-growth by electrochemical induction. Furthermore, the electrode only requires an overpotential of 340 mV at 10 mA cm⁻² in 0.5 M Na₂CO₃/NaHCO₃ solution. It is expectable that the modified SSF will be a promising catalysis electrode for water-electrolysis in large-scale commercial production.     

Three-dimensional hierarchically porous iridium oxide-nitrogen doped carbon hybrid: An efficient bifunctional catalyst for oxygen evolution and hydrogen evolution reaction in acid

Active and durable acid medium electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are of critical importance for the development of proton exchange membrane (PEM) water electrolyser or Fuel cells. Herein, we report a facile method for the synthesis of 3D-hierarchical porous iridium oxide/N-doped carbon hybrid (3D-IrO₂/N@C) and its superior OER and HER activity in acid. In 0.5 M HClO₄, this catalyst exhibited remarkable activity towards OER with a low overpotential of 280 mV at 10 mA/cm² current density, a low Tafel slope of 45 mV/dec and ∼98% faradaic efficiency. The mass activity (MA) and turnover frequency (TOF) are found to be 833 mA/mg and 0.432 s⁻¹ at overpotential of 350 mV which are ∼32 times higher than commercial (comm.) IrO₂. The HER performance of this 3D-IrO₂/N@C is comparable with comm. Pt/C catalyst in acid. This 3D-IrO₂/N@C catalyst requires only 35 mV overpotential to reach a current density 10 mA/cm² with Tafel slope 31 mV/dec. Most importantly, chronoamperometric stability test confirmed superior stability of this catalyst towards HER and OER in acid. This 3D-IrO₂/N@C catalyst was applied as both cathode and anode for over-all water splitting and required only 1.55 V overpotential to achieve a current density of 10 mA/cm² in acid. The outstanding activity of the 3D-IrO₂/N@C catalyst can be attributed to a unique hierarchical porous network, high surface area, higher electron and mass transportation, synergistic interaction between IrO₂ and carbon support.     

Mesoporous nickel-sulfide/nickel/N-doped carbon as HER and OER bifunctional electrocatalyst for water electrolysis

The development of non-precious metal-based highly active bi-functional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is critical factor for making water electrolysis a viable process for large-scale industrial applications. In this study, bi-functional water splitting electrocatalysts in the form of nickel-sulfide/nickel nanoparticles integrated into a three-dimensional N-doped porous carbon matrix, are prepared using NaCl as a porous structure-forming template. Microstructures of the catalytic materials are characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and N₂ adsorption-desorption analysis. The most active catalyst synthesized in this study exhibits a low HER overpotential of 70 mV at 10 mA cm⁻² and a low Tafel slope of 45 mV dec⁻¹. In OER, the optimized sample performs better than a state-of-the-art RuO₂ catalyst and produces an overpotential of 337 mV at 10 mA cm⁻², lower than that of RuO₂. The newly obtained materials are also used as HER/OER electrocatalysts in a specially assembled two-electrode water splitting cell. The cell demonstrates high activity and good stability in overall water splitting.     

Preparation of ultrathin molybdenum disulfide dispersed on graphene via cobalt doping: A bifunctional catalyst for hydrogen and oxygen evolution reaction

The development of highly active and low-cost catalysts for hydrogen evolution reaction (HER) is significant for the development of clean and renewable energy research. Owing to the low H adsorption free energy, molybdenum disulfide (MoS₂) is regarded as a promising candidate for HER, but it shows low activity for oxygen evolution reaction (OER). Herein, graphene-supported cobalt-doped ultrathin molybdenum disulfide (Co–MoS₂/rGO) was synthesized via a one-pot hydrothermal method. The obtained hybrids modified electrode exhibits a high HER catalytic activity with a low overpotential of 147 mV at the current density of 10 mA cm⁻², a small Tafel slope of 49.5 mV dec⁻¹, as well as good electrochemical stability in acidic electrolyte. Meanwhile, the catalyst shows remarkable OER activity with a low overpotential of 347 mV at 10 mA cm⁻². The superior activity is ascribed not only to the high conductivity originated from the reduced graphene, but also to the synergistic effect between MoS₂ and cobalt.