Metal–organic framework-derived Co@NMPC as efficient electrocatalyst for hydrogen evolution reaction: Revealing the synergic effect of pyridinic N–Co

Developing hydrogen economy is one of the feasible routes to reduce carbon emission in response to the energy crisis and global warming. The hydrogen generation by electrochemical water splitting has received widespread attention, but it is still challenging to fabricate high-efficient electrocatalysts to decrease the kinetic energy barrier of hydrogen evolution reaction (HER). Loading transition metal (TM) nanoparticles (NPs) into heteroatom-doped carbon materials (HCM) has been reported as a capable scheme to increase the electrochemical activity and stability, but the synergic effect between TM surface and HCM is still worth exploring. Ascertaining that, we used metal-organic frameworks (MOFs) as the sacrificial precursor to synthesis a series of Co NPs encapsulated in N-doped microporous carbon (NMPC) nanocatalysts (denoted as Co@NMPC) with different N species (such as pyrrolic, pyridinic and graphitic N). The nanocatalyst prepared at an appropriate condition displayed an outstanding HER activity with an overpotential of 193 mV in 1 M KOH solution and 132 mV in 0.5 M H₂SO₄ solution to reach 10 mA cm^?2 current density. Furthermore, the results of in situ shielding tests indicate that the synergy of pyridinic N–Co site owing to the intimate contact between Co surface and NMPC play the pivotal role in boosting HER performance. Density functional theory (DFT) calculations were employed to obtain an in-depth mechanism of synergic effect between Co and NMPC.     

Electrocatalytic hydrogen evolution on iron-cobalt nanoparticles encapsulated in nitrogenated carbon nanotube

Using low-cost nonprecious metals to replace Pt as hydrogen evolution reaction (HER) electrocatalyst is promising, but still limited by their efficiency and stability. Herein, with low-cost dicyandiamide and metal salts as precursor, FeCo alloy nanoparticles encapsulated in nitrogenated carbon nanotubes (FeCo-NCNTs) were facially synthesized as efficient HER electrocatalyst. Addition of iron as second element, though not facilitating the formation of carbon nanotube, was utilized to improve the physicochemical properties of metals. Via optimizing the atomic molar ratios of Fe/Co nanoparticles, the optimal Fe_0.4Co_0.6-NCNTs with thin carbon shell (c.a. 5–10 layer) and equally distribution of embedded alloy nanoparticles was found with outstanding HER activity. To achieve a current density of 10 mA cm⁻², only overpotential of 50 mV, 157 mV and 202 mV were needed in acidic (0.5 M H₂SO₄), alkaline (1 M KOH), and neutral solutions. Its higher electrochemically active surface areas and lower electron transfer resistance may contribute to the excellent electrocatalytic HER. Furthermore, the illustrated current density slightly changed over 20 h, suggesting excellent stability. Hence, the present method provides cost-effective, high efficiency, and stable materials in developing the sustainable energy conversion systems.     

Uniform cobalt nanoparticles embedded in nitrogen-doped graphene with abundant defects as high-performance bifunctional electrocatalyst in overall water splitting

Co nanoparticles with uniform size (about 5 nm) embedded in N-doped graphene (Co-NG) were explored in this work. The introduction of a second carbon source of citric acid during synthesis prevented the Co atoms from growing up, thus regulating the size of the cobalt nanoparticles. N atoms in N-doped graphene had more lone-pair electrons, making it easier to capture electrons from hydrated ions, and facilitating the dynamics procedure of HER. Furthermore, N dopant rendered larger positive charge density on the adjacent carbon atoms, which was conducive to OER and HER. At 10 mA cm^?2 of the current density, the Co-NG/CC catalyst's overvoltage of HER was 78 mV, approaching that of 20% Pt/C (59 mV), an efficient precious metal electrocatalyst for HER, while its overvoltage of OER was about 225 mV, 12.5% lower than that of RuO₂ (257 mV, a common precious metal oxide OER electrocatalyst). In addition, this Co-NG/CC composite bifunctional catalyst displayed good electrochemical stability in alkali solution and might be designed as a dual-function catalyst in the application of overall water splitting. The cell voltage of Co-NG/CC//Co-NG/CC was only 1.66 V, approaching to that of full precious metal cell of Pt/C//RuO₂ (1.52 V), and revealing the good commercial application prospects of this composite bifunctional catalyst.     

Hollow bimetallic M-Fe-P (M=Mn,Co, Cu) nanoparticles as efficient electrocatalysts for hydrogen evolution reaction

Searching for low-cost electrocatalysts with high activity towards the hydrogen evolution reaction (HER) is of great significance to enable large-scale hydrogen production via water electrolysis. In this study, by using inverse spinel MFe₂O₄(M = Mn, Fe, Co, Cu) nanoparticles (NPs) as the precursors, monodisperse bimetallic phosphide M-Fe-P NPs/C with hollow structures were readily obtained by a gas-solid annealing method. These hollow phosphide NPs displayed excellent HER activity in an acidic medium with a low loading amount of 0.2 mg cm⁻². In particular, the Co–Fe–P NPs/C shows highest HER activity that only requiring an overpotential of 97 mV to retain a current density of 10 mA cm⁻². A volcano relation between activity and incorporated elements was revealed. Incorporation of cation with high electronegativity stabilized the FeP active centres, while phase segregation resulted in the loss of activity for Cu–Fe–P NPs/C.     

Structural engineering of hierarchically hetestructured Mo2C/Co conformally embedded in carbon for efficient water splitting

Developing low-cost and high efficient electrocatalysts for both oxygen and hydrogen evolution reaction in an alkaline electrolyte toward overall water splitting is still a significant challenge. Here, a novel hierarchically heterostructured catalyst composed of ultrasmall Mo₂C and metallic Co nanoparticles confined within a carbon layer is produced by a facile phase separation strategy. During thermal reduction of CoMoO₄ nanosheets in CO ambient, in-situ generated nanoscale Co and ultrafine Mo₂C conformally encapsulated in a conductive carbon layer. In addition, some carbon nanotubes catalyzed by Co nanoparticles vertically grew on its surface, creating 3D interconnected electron channels. More importantly, the integrated C@Mo₂C/Co nanosheets assembled into the hierarchical architecture, providing abundant active surface and retaining the structural integrity. Benefiting from such unique structure, the constructed hierarchical heterostructure shows low overpotentials of 280 mV and 145 mV to reach a current density of 10 mA cm⁻² for OER and HER in an alkaline electrolyte. Furthermore, the symmetrical electrolyzer assembled with catalyst exhibits a small cell voltage of 1.67 V at 10 mA cm⁻² in addition to outstanding durability, demonstrating the great potential as a high efficient bifunctional electrocatalyst for overall water splitting.     

Low loading of P modified Rh nanoparticles encapsulated in N,P-doped carbon for boosted and pH-universal hydrogen evolution reaction

Searching for highly efficient and Pt-free electrocatalysts with comparable hydrogen evolution reaction (HER) activities to the benchmark Pt/C catalyst is highly demanded for developing renewable water electrolysis system but still remains challenging. In the current work, low loading of P modified ultrafine Rh nanoparticles encapsulated in N, P dual-doped carbon layers (Rh–P@NPC) have been prepared through a facile polymerization-impregnation followed by high-temperature pyrolysis process. Benefiting from the unique core-shell structural advantages and synergistic effect of Rh–P and NPC components, the resulting Rh–P@NPC catalyst not only exhibits remarkable electrocatalytic activity for HER in the whole pH range with a low overpotential of 31 mV, 65 mV, and 130 mV to drive a current density of 10 mA cm^?2 in 0.5 M H₂SO₄, 1.0 M KOH, and 1.0 M PBS, respectively, but also demonstrates high durability. It is worth to note that all these HER performances are on a par with commercial Pt/C catalysts for HER. This synthetic strategy provides possibility for the fabrication of carbon-based heterostructures with high catalytic activity and durability in harsh environments.     

3D hierarchical nanostructured Ni–Co alloy electrodes on porous nickel for hydrogen evolution reaction

Nanostructured Ni–Co alloys decorated on 3D porous nickel electrodes for hydrogen evolution reaction (HER) are successfully prepared through a facile and effective electrodeposition method. By adjusting the current density of electrodeposition, Ni–Co alloys with different surface morphologies like nanocones, leaf-like structures and flakes can be obtained. The HER catalytic activity has been greatly reinforced with decorated Ni–Co alloys. Meanwhile, the HER performance of nanocone Ni–Co alloys outperforms that of leaf-like and flaky Ni–Co alloys. The nanocone Ni–Co alloys exhibit outstanding HER activity, only requiring an overpotential of 86.7 mV at 10 mA cm⁻², along with a low Tafel slope of 69.8 mV dec⁻¹ and 3.4 Ω charge transfer resistance. This nanocone electrode remains stable for 10 h of chronopotentiometric measurement. Such enhanced catalytic performance stems from the porosity and the high population of sharp edges, as well as surface oxidation/metallic states and synergistic effects between Ni and Co.     

Ultrafine Ru nanoparticles derived from few-layered Ti3C2Tx MXene templated MOF for highly efficient alkaline hydrogen evolution

It is meaningful to search high-efficient and inexpensive electrocatalysts for hydrogen evolution reaction (HER) due to the energy crisis and environmental pollution. Here, we report the preparation of ultrafine Ru nanoparticles from a hybrid of ZIF-L(Co) MOF and polydopamine coated few-layered Ti₃C₂T_x MXene (FL-Ti₃C₂T_x). FL-Ti₃C₂T_x is used as a template to grow regular leaf-shaped ZIF-L(Co) nanosheets through the reaction of Co ions anchored on the MXene surface with 2-methylimidazole. The obtained hybrid is then doped with Ru ions through ion exchange between Ru and Co ions, followed by thermal annealing at a temperature of 350 °C in an Ar atmosphere to produce ultrafine Ru nanoparticles. The obtained Ru@ZIF-L(Co)/FL-Ti₃C₂T_x nanocomposite shows outstanding HER performance with a low overpotential of 16.2 mV at a current density of 10 mA cm^?2, a small Tafel slope of 21.0 mV dec^?1 and excellent stability in 1.0 M KOH solution. This work provides a new strategy for the design and synthesis of highly efficient HER catalyst via MOFs with tunable composition and structure.     

A novel in-situ strategy develops for Mo2C nanoparticles incorporated on N,P co-doped stereotaxically carbon as efficient electrocatalyst for overall water splitting

Developing cost-effective and remarkable electrocatalysts toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performs excelling role in boosting the hydrogen energy application. Herein, a novel in-situ one-pot strategy is developed for the first time to synthesize molybdenum carbide nanoparticles (Mo₂C NPs) incorporated on nitrogen (N) and phosphorous (P) co-doped stereotaxically carbon (SC). The optimized Mo₂C NPs/N, P–SC–800 electrocatalyst exhibits lower overpotentials of 131 and 287 mV for HER and OER to deliver a current density of 10 mA cm^?2 in 1.0 M KOH medium with smaller Tafel slopes of 58.9 and 74.4 mV/dec, respectively. In addition, an electrolyzer using Mo₂C NPs/N, P–SC–800 electrode as cathode and anode delivers a current density of 10 mA cm^?2 at a small voltage of 1.64 V for overall water splitting. The excellent water splitting performance could be ascribed to optimum Mo₂C NPs for more accessible active sites, highly active N, P-SC networks for accelerated electron transfers, and synergetic effect between Mo₂C NPs and N, P-SC networks. The N, P-SC network not only enhances the overall dispersion of Mo₂C NPs but also contributes numerous electroactive edges to enhance the performance of HER, OER, and overall water splitting activity. This research work explores the in-situ one-step strategies of advanced, cost-effective, and non-precious metal electrocatalysts for efficient water splitting and motivates the consideration of a novel class of heteroatom doped stereotaxically carbon nanocomposites for sustainable energy production.     

Metal-organic framework derived Co@NC/CNT hybrid as a multifunctional electrocatalyst for hydrogen and oxygen evolution reaction and oxygen reduction reaction

Seeking a multifunctional electrocatalyst composed of earth-abundant elements for highly hydrogen and oxygen evolution reaction and oxygen reduction reaction (HER, OER and ORR) is technically imperative for the electrocatalytic applications. Herein, we report HER, OER and ORR electrocatalytic performances of metal-organic framework (MOF) derived cobalt nanoparticles encapsulated in nitrogen-doped carbon and carbon nanotube (Co@NC/CNT). The optimized Co@NC/CNT hybrid shows superior HER and OER activities with a small overpotential of 137 mV and 302 mV at a current density of 10 mA cm⁻², respectively. Furthermore, the Co@NC/CNT as an air-cathode in secondary Zn-air battery demonstrates a confined potential gap of 0.88 V over 200 h and a maximum power density of 53.4 mW cm⁻², which are much better than those of Pt/C. The outstanding performances are attributed to the synergistic effects from Co, and N embedded into carbon and CNT. More importantly, the unique surface structure contributes to expose many active sites for superior catalytic activity through allowing a large number of electrons. These outcomes not only prove a facile approach for the preparation of metals/carbon hybrid but also disclose its huge possible as a multifunctional electrocatalyst for sustainable energy systems.     

RhRu alloyed nanoparticles confined within metal organic frameworks for electrochemical hydrogen evolution at all pH values

As an effective way to generate high-purity hydrogen through water electrolysis, electrochemical hydrogen evolution reaction (HER) underpins various clean-energy technologies. Nevertheless, most of the currently reported HER catalysts only exhibited good activity in a narrow pH range (e. g. in acid electrolyte). Thence, developing high-performance electrocatalysts for HER at all pH values is significant and imperative. Herein, we report an active electrocatalyst of Rh_xRu_100-x@UiO-66-NH₂ (x denotes the initial atomic percentage of Rh in RhRu alloys) by in-situ confining RhRu binary alloys within metal-organic framework (MOF) of UiO-66-NH₂. Among the Rh_xRu_100-x@UiO-66-NH₂ samples, Rh₅₀Ru₅₀@UiO-66-NH₂ exhibited the most outstanding HER performance at all pH values, as well as comparable activity and outperformed stability to the commercial Ru/C and Pt/C catalysts. In HER tests, Rh₅₀Ru₅₀@UiO-66-NH₂ displayed an overpotential of 77 mV, 114 mV and 177 mV at the current density of 10 mA cm⁻² in 0.5 M H₂SO₄ (pH = 0.53), 1 M PBS (pH = 7) and 1 M KOH (pH = 14) solutions, respectively. The strategy for confining metal nanoparticles within the cavities of MOFs can enrich the toolbox for design and construction of low cost, efficient, and environment-friendly catalysts for hydrogen production toward clean energy applications.     

Carbon nanorod supported metal alloy nanocubes using polydopamine as location reagent for water splitting

Transition metal catalysts were supposed to be the most likely substitute for commercial noble metal catalysts, and the development of highly active and long-term catalyst for water splitting are the future trend. Herein, Ni rectangular nitrogen doped carbon nanorods@Fe–Co nanocubes (Ni-CNRs@Fe–Co cubes) were fabricated via a facile template-free method. This simple strategy not only realizes the structure tailoring, but also achieves high-quality nitrogen-doping. Specifically, nickel dimethylglyoxime [Ni(dmg)₂] with rectangular rodlike structure was firstly synthesized by solution method, then metal-organic frameworks Fe–Co nanocube with different contents were loaded on rectangular carbon nanorods with polydopamine as the locating and the connecting agent, and finally Ni-CNRs@xFe-Co cubes were obtained by a one-step calcination. A series of electrochemical tests were researched on materials with different metal contents in the 1 M KOH solution. The Ni-CNRs@Fe–Co cubes show excellent electrocatalytic activity in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). For HER and OER, the Tafel slopes were 83.3 mV dec⁻¹ and 71 mV dec⁻¹, the onset potential were −167 mV and 1.62 V, and reached the current densities of 10 mA cm⁻², the overpotential just needed 196 mV and 433 mV, respectively. This novel synthetic strategy will provide a template-free way for cheap electrocatalysts of non-precious metal for OER and HER.     

Co/VN heterostructure coated with holey interconnected carbon frameworks as bifunctional catalysts

The development of transition-metal electrocatalyst is of great importance to bring down costs and enhance performance for fuel cells and water splitting. The multiple efforts have been concentrated on bifunctional electrocatalysts toward hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). Only a few works reach desirable durability and performance levels. Here, Co/VN heterostructure with rational porous structure is formed in response to the sensible cobalt and vanadium ratio. Owing to synergistic interaction of holey interconnected structure with large surface area of 57 m² g^?1 and abundant interfaces between Co and VN phases, Co/VN@NC presents superior bifunctional electrocatalytic performance towards both HER and ORR. Co/VN@NC drives the reaction with low overpotential η₁₀ of 96 mV and Tafel slope of 82 mV dec^?1 along with outstanding stability for HER. Furthermore, Co/VN@NC obtains an onset potential (0.954 V) and half-wave potential (0.796 V) with superior methanol tolerance and durability for ORR.     

Mo-chelate strategy for synthesizing ultrasmall Mo2C nanoparticles embedded in carbon nanosheets for efficient hydrogen evolution

Production of hydrogen from electrochemical water splitting has been regarded as one of the most economic and sustainable techniques for green fuel production. It is significant and challengeable to develop highly efficient and low cost noble metal-free electrocatalysts. Presently, molybdenum-based electrocatalysts were regarded as potential alternatives for the hydrogen evolution reaction (HER). Here, the well-dispersed and ultrasmall Mo₂C nanoparticles (NPs) anchored on 2D carbon nanosheets were synthesized by designing chelate precursor and following pyrolysis, which was proved to be an effective approach for preparing carbon-loaded Mo₂C NPs. The as-obtained Mo₂C/C material exhibits an outstanding activity and stability in hydrogen evolution reaction (HER). It needs an overpotential of 147 mV to drive 10 mA cm⁻² and Tafel slope is 64.2 mV dec⁻¹ in alkaline medium, implying that Mo₂C/C material will be a potential noble metal-free electrocatalyst for HER. The design of Mo-chelate precursor is a feasible route to synthesize ultrafine Mo₂C and it can provide a reference for synthesizing other nanoparticles and hindering particle coalescence at high preparation temperature.     

CO2 assisted synthesis of silk fibroin driven robust N-doped carbon aerogels coupled with nickel–cobalt particles as highly active electrocatalysts for HER

Hydrogen evolution reaction (HER), has been considered as an ideal alternative energy system to alleviate the global energy crisis. Unfortunately, the rational design of a cost-effective, highly active and stable electrocatalyst remains a tough challenge. In this work, a CO₂ assisted synthesis of N- doped carbon aerogel derived from silk fibroin (SFCA) without any additives was used to anchor Nickel–Cobalt (NiCo) nanoparticles as an HER electrocatalyst in basic medium (1 M KOH). The obtained SFCA-NiCo electrocatalyst demonstrated outstanding electrochemical performance having an onset potential of 52 mV and a low overpotential of 179 mV at current density of 10 mA cm^?2, whilst exhibiting long term stability when tested for 24 h. The outstanding electrocatalytic performance marks SFCA-NiCo as a favourable electrocatalyst for HER and the synthesis strategy paves way for constructing novel catalysts even for other areas.     

Mo2C regulated by cobalt components doping in N-doped hollow carbon nanofibers as an efficient electrocatalyst for hydrogen evolution reaction

Hydrogen is a viable substitute to fossil fuels and electrochemically catalyzed hydrogen evolution has attracted wide attention due to its stability and effectiveness. Nevertheless it is still a major challenge to design and prepare highly active noble metal-free electrocatalysts with controllable structure and composition for efficient hydrogen evolution reaction (HER). Herein, Mo₂C regulated by cobalt components (Co and CoO) doping in N-doped hollow carbon nanofibers (marked as Mo₂C/Co/CoO-NHCNFs) are firstly designed and prepared via a facile coaxial electrospinning followed by calcination process. The one-dimensional conductive carbon host, hollow structure and synergistic effect among CoO, Co and Mo₂C can jointly promote electron transfer, augment exposure of active sites and adjust the electronic structure of the active sites, resulting in the excellent of HER performances. The optimized catalyst has a high specific surface area of 101.27 m² g^?1. Meanwhile, it has a low overpotential of 143 mV at a current density of 10 mA cm^?2 and a small Tafel slope of 74 mV dec^?1 in 1.0 M KOH.Satisfactorily, the overpotential is reduced by 231 mV at the same current density compared with Mo₂C doped in N-doped carbon nanofibers (named as Mo₂C-NCNFs). Moreover, the Mo₂C/Co/CoO-NHCNFs also demonstrate superior long-term stability. The formative mechanism of Mo₂C/Co/CoO-NHCNFs is expounded, and the construction technique is established. The design philosophy and the simple and economical method are of significance for development of HER electrocatalysts.     

Electrocatalytic performances of oxygen-deficient titanium dioxide nanosheet coupled palladium nanoparticles for oxygen reduction and hydrogen evolution reactions

The development of multifunctional electrocatalysts is crucial for enhancing the efficiency of electrochemical conversion in energy devices. Here we have synthesized TiO_2-x nanosheets (NSs) supported metallic Pd nanoparticles (Pd/TiO_2-x NSs) as an electrocatalyst using a simple impregnation process. High electrochemical surface areas (ECSAs) and strong metal support interactions (SMSI) of the electrocatalyst showed improved ORR performance throughout a wide pH range under ambient conditions. The outstanding durability of the catalyst was proven by the square-wave potential cycling experiment at 60 °C. Additionally, it was shown that Pd/TiO_2-x NSs showed improved HER activity and stability in 0.5 M H₂SO₄. The catalyst had an overpotential of 19.5 mV for the 10 mA cm⁻² and a low Tafel slope of 41 mV dec⁻¹. The catalyst also showed higher stability for about 30 h in HER performance. This work will help in rationally building nanostructured electrocatalysts loaded on carbon-free support for efficient electrochemical energy storage devices.     

N-doped graphene supported W2C/WC as efficient electrocatalyst for hydrogen evolution reaction

Tungsten carbides (W₂C and WC) materials, as promising non-precious electrocatalysts, possess highly efficient activity for HER. Herein, N-doped graphene supported tungsten carbide (N–W₂C/WC) nanocomposite is synthesized by spray drying process followed with a two-step pyrolysis treatment, which exhibits a remarkable hydrogen evolution reaction (HER) activity and excellent stability in acidic solution and alkaline solution. N–W₂C/WC displays low overpotentials of 166 mV and 125 mV to achieve a current density of 10 mA cm^?2 and small Tafel slopes of 60.97 and 62.66 mV dec^?1 in 0.5 M H₂SO₄ and 1.0 M KOH, respectively. After 1000 cycles, the electrocatalytic activity of N–W₂C/WC is almost no change in acidic media but slightly decreases in alkaline media. This work might provide a new way to explore high comprehensive performance tungsten-based electrocatalyst for HER.     

Polyaniline grafted mesoporous zinc sulfide nanoparticles for hydrogen evolution reaction

Numerous efforts have been directed to fabricate the cost-effective structure for hydrogen evolution reaction (HER). However, it is still a challenging task for clean energy. Herein, mesoporous zinc sulfide nanoparticles with various contents of polyaniline have been synthesized using the solvothermal process. Morphological and structural analysis has been carried out in detail for HER activity in KOH electrolyte at pH 10.20 and 13.55. The hybrid of zinc sulfide and Polyaniline (ZnS-90 mg), exhibits a lower specific surface area of 5.54 m² g^-1 and a greater mesoporous size of 10.10 nm as compared to individual polyaniline nanofibers (75.13 m² g^-1 and 6.02 nm) and zinc sulfide nanoparticles (80.90 m² g^-1 and 6.81 nm) due to interface, which creates the unique characteristics as compared to PANI-Nbs and ZnS-NPs. Hybrid ZnS-90 mg, synergistically, exhibits the greater electrical conductivity of 17.90 × 10^?4 Scm^?1 and reveals the lower over potential of 168 mV with an onset potential of 41 mV at pH 13.55, and an over potential of 345 mV with an onset potential of 69 mV at pH 10.20 of 1 M KOH for HER activity at the state of art current density of 10 mAcm^?2. Hybrid ZnS-90 mg also shows the smaller Tafel slope of 234 mVdec^?1 with the greater turnover frequency of 5.22 ms^-1 at pH 13.55, recommending the better HER activity. A symmetric system consisting of Hybrid ZnS-90 mg reveals the two reduction peaks, where the over potential has been measured as 524 mV at the current density of 2.76 mAcm^?2 and 947 mV at the current density of 10 mAcm^?2 at pH 13.55. The symmetric system exhibits a good Tafel slope of 26 mVdec^?1 and suggests it is the suitable and cost-effective electrode structure for HER to produce clean hydrogen energy.     

Structure-design and synthesis of nickel-cobalt oxide/sulfide/phosphide composite nanowire arrays for efficient overall water splitting

The construction of cost-effective bifunctional electrocatalysts with the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is significant for efficient overall water splitting. Herein, this work demonstrates a novel strategy for the synthesis of nickel-cobalt oxides/sulfides/phosphides composite (denoted as NiCoO–2P/S) nanoarrays on Ni foam. In this method, Ni–Co bimetallic oxide nanowires on Ni foam were partially phosphorized and sulfurized simultaneously in situ to yield Ni–Co oxide/sulfide/phosphide composite. The NiCoO–2P/S arrays have good interfacial effects and display many holes in the nanowires, giving it the advantage of large accessible surfaces on the nanowires and a beneficial for the release of gas bubbles, resulting in an excellent OER performance with a low overpotential (η) of 254 mV at 100 mA cm^?2 and good HER activity (η₁₀ = 143 mV at 10 mA cm^?2). The electrocatalytic test results demonstrate small Tafel slopes (82 mV dec^?1 for HER, 88 mV dec^?1 for OER) and the satisfying durability in an alkaline electrolyte, indicating that the HER and OER activity was enhanced by the introduction of the Ni/Co sulfides and phosphides into Ni–Co oxides composite nanowires. Furthermore, the as-prepared NiCoO–2P/S catalyst can be used as both the anode and the cathode simultaneously to realize overall water splitting in the two-electrode electrolyzer. This system can be driven at low cell voltages of 1.50 and 1.68 V to achieve current densities of 10 and 100 mA cm^?2, respectively. This work provides an alternative strategy to prepare high-performance bifunctional electrochemical materials and demonstrates the advantages of Ni–Co oxide/sulfide/phosphide composites for water splitting.