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.     

One-step fabrication of heterostructured CoNi-LDH@NiCo alloy for effective alkaline hydrogen evolution

Construction of heterostructured electrocatalyst with interface effect is an effective strategy for enhancing the alkaline hydrogen evolution efficiency, whereas this process often requires complex treatments. Herein, we proposed a one-step electrodeposition method to obtain heterostructured CoNi-LDH@NiCo alloy on Ni foam (NF) through a competition reduction between NO₃^? group and metal cations in the electrolyte. The HER performance for the CoNi-LDH@NiCo alloy achieved the current density of 10 mA cm^?2 at overpotential of 69 mV in 1 M KOH solution, improved 60% for η₁₀ by comparing with the pristine NiCo alloy. Utilizing the specialized adsorption of CoNi-LDH for H₂O and the featured attractiveness of NiCo alloy for H atom, the interface effect of the heterostructure electrocatalyst accelerated the dissociation of water molecules and elevated the catalytic kinetics dramatically. This work points out a potential approach towards the easy construction of inexpensive heterostructured electrocatalysts for HER activity in alkaline medium.     

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.     

Metal-organic frameworks derived self-supported Ni2P nanorod arrays for electrocatalytic hydrogen evolution

The development of efficient and low-cost electrocatalysts for hydrogen evolution reaction (HER) is of importance. Herein, we demonstrate a self-supported Ni₂P nanostructure with nanorod arrays morphology, fabricated by directly growing metal-organic frameworks (MOFs) on the commercial nickel foam prior to phosphorization treatment, as an electrocatalyst for HER. This electrocatalyst exhibits remarkable electrocatalytic HER activity in an alkaline electrolyte, affording current densities of 10 and 100 mA cm^?2 at the overpotentials of 120 and 168 mV, respectively, accompanied with a low Tafel slope of 37 mV dec^?1. Furthermore, this electrocatalyst shows a current density of 105 mA cm^?2, and this current density can be retained for more than 20 h, suggesting its superior stability. This remarkable HER performance is believed a result of superiority for its structural integrality and mechanical stability.     

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.     

High throughput preparation of Ni–Mo alloy thin films as efficient bifunctional electrocatalysts for water splitting

The synthesis of cost-effective and high-performance electrocatalysts for water splitting is the main challenge in electrochemical hydrogen production. In this study, we adopted a high throughput method to prepare bi-metallic catalysts for oxygen/hydrogen evolution reactions (OER/HER). A series of Ni–Mo alloy electrocatalysts with tunable compositions were prepared by a simple co-sputtering method. Due to the synergistic effect between Ni and Mo, the intrinsic electrocatalytic activity of the Ni–Mo alloy electrocatalysts is improved, resulting in excellent HER and OER performances. The Ni₉₀Mo₁₀ electrocatalyst shows the best HER performance, with an extremely low overpotential of 58 mV at 10 mA cm^?2, while the Ni₄₀Mo₆₀ electrocatalyst shows an overpotential of 258 mV at 10 mA cm^?2 in OER. More significantly, the assembled Ni₄₀Mo₆₀//Ni₉₀Mo₁₀ electrolyzer only needs a cell voltage of 1.57 V to reach 10 mA cm^?2 for overall water splitting.     

Ni activated Mo2C nanoparticles supported on stereotaxically-constructed graphene for efficient overall water splitting

Exploring cost-effective, high-efficiency and stable electrocatalysts for overall water splitting is greatly desirable and challenging for sustainable energy. Herein, a novel designed Ni activated molybdenum carbide nanoparticle loaded on stereotaxically-constructed graphene (SCG) using two steps facile strategy (hydrothermal and carbonization) as a bifunctional electrocatalyst for overall water splitting. The optimized Ni/Mo₂C(1:20)-SCG composites exhibit excellent performance with a low overpotential of 150 mV and 330 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively to obtain a current density of 10 mA cm^?2 in 1.0 M KOH solution. In addition, when the optimized Ni/Mo₂C(1:20)-SCG composite is used as a bifunctional electrode for overall water splitting, the electrochemical cell required a low cell voltage of 1.68 V at a current density of 10 mA cm^?2 and long-term stability of 24 h. More significantly, the synergetic effects between Ni-activated Mo₂C nanoparticles and SCG are regarded as a significant contributor to accelerate charge transfer and promote electrocatalytic performance in hybrid electrocatalysts. Our works introduce a novel approach to design advanced bifunctional electrodes for overall water splitting.     

Efficient CoMoRu0.25Ox/NF nanoplate architectures for overall electrochemical water splitting

The development of inexpensive electrocatalysts with excellent electrocatalytic activity for the hydrogen and oxygen evolution reactions (HER and OER, respectively) has been challenging. In this study, we synthesized cobalt molybdenum ruthenium oxide with porous, loosely-assembled nanoplate morphology. The CoMoRu_0.25O_x/NF electrocatalyst exhibited the highest electrocatalytic activity, requiring overpotentials of 230 and 78 mV for the OER and HER, respectively, to attain a current density of 10 mA cm^?2; moreover, its long-term stability was outstanding. The electrocatalyst required a cell voltage of only 1.51 V for overall water splitting in an alkaline medium, which was lower than that required by many CoMo-based catalysts.     

Rational design of Ni-induced NC @Mo2C@MoS2 sphere electrocatalyst for efficient hydrogen evolution reaction in acidic and alkaline media

Exploiting efficient and low-cost electrocatalyst for Hydrogen Evolution Reaction (HER) of water electrolysis remains a challenge. Herein, we designed an efficient electrocatalyst of Ni-induced nitrogen-doped carbon @ molybdenum carbide @ molybdenum disulfide sphere (NC@Mo₂C@MoS₂-(Ni)) by two simple coating steps following pyrolysis process. Benefiting from the regular spherical morphology, unique structure, synergistic effect between Mo₂C and MoS₂, inducement effect of elemental Ni that initial added and removed in final synthesis procedure, heteroatom N and P doping. The catalyst NC@Mo₂C@MoS₂-(Ni) exhibits relatively good catalytic performance of overpotentials of 205 and 216 mV at 10 mA cm^?2 and Tafel slopes of 61.4 and 42.7 mV dec^?1 in acidic and basic media, respectively. This work not only fabricate the electrocatalyst of NC@Mo₂C@MoS₂-(Ni) towards HER, but also provides a way to rationally design more efficient other functional electrocatalysts.     

3D self-standing grass-like cobalt phosphide vesicles-decorated nanocones grown on Ni-foam as an efficient electrocatalyst for hydrogen evolution reaction

The growing hydrogen consumption has greatly promoted the development of efficient, stable and low-cost electrocatalysts for the hydrogen evolution reaction (HER). Constructing functional nanostructures is an efficacious strategy to optimize catalytic performance. Herein, we present a feasible route to fabricate distinctive 3D grass-like cobalt phosphide nanocones clad with mini-vesicles on the hierarchically porous Ni foam, which can directly serve as a binder-free electrocatalyst with superior catalytic activity and durability in HER. Thanks to its distinctive 3D microstructure featured with favourable pore-size distribution, abundant active sites provided by mini-vesicles and rapid electron transfer with the assistance of Ni foam, the as-grown grass-like CoP/NF electrocatalyst has shown a favourable overpotential in an acidic solution with an onset overpotential of ∼35 mV, an overpotential of 71 mV at a current density of 10 mA cm⁻², reduced by 60 mV in comparison with that realized by urchin-like CoP/NF nanoprickles. Moreover, it has exhibited an excellent HER activity in the alkaline medium, with an overpotential of 117 mV at 10 mA cm⁻², a Tafel slope of 63.0 mV dec⁻¹ and a long-term electrochemical durability.     

Growth of porous single-crystalline molybdenum nitrides microcubes with enhanced electrocatalysis performance

Porous single crystal has the characteristics of long-range order, continuous lattice and large specific surface area, which could reduce energy losses and keep high activity and stability in electrochemical systems. Here, we grow porous single-crystalline and polycrystalline molybdenum nitrides microcubes from MoO₃ single crystals. These porous microcubes show superior HER and OER performance. The overpotential of Mo₂N porous single crystal microcubes is only 73.13 mV at a current density of 10 mA cm^?2, which is 150.53 mV, 192.76 mV and 255.87 mV lower than that of MoN single crystal, Mo₂N polycrystal and MoN polycrystal, respectively. The advantages of Mo₂N porous single crystals in electrocatalytic properties are also reflected in OER.     

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.     

Bifunctional nanoporous ruthenium-nickel alloy nanowire electrocatalysts towards oxygen/hydrogen evolution reaction

A class of ruthenium-nickel alloy catalysts featured with nanoporous nanowires (NPNWs) were synthesized by a strategy combining rapid solidification with two-step dealloying. RuNi NPNWs exhibit excellent electrocatalytic activity and stability for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in which the RuNi-2500 NPNWs catalyst shows an OER overpotential of 327 mV to deliver a current density of 10 mA cm^?2 and the RuNi-0 NPNWs catalyst requires the overpotential of 69 mV at 10 mA cm^?2 showing the best HER activity in alkaline media. Moreover, the RuNi-1500 NPNWs catalyst was used as the bifunctional electrocatalyst in a two-electrode alkaline electrolyzer for water splitting, which exhibits a low cell voltage of 1.553 V and a long-term stability of 24 h at 10 mA cm^?2, demonstrating that the RuNi NPNWs catalysts can be considered as promising bifunctional alkaline electrocatalysts.     

Cobalt nanoparticles encapsulated in nitrogen-rich carbonitride nanotubes for efficient and stable hydrogen evolution reaction at all pH values

Developing non-precious and high-efficiency Pt free electrocatalysts for the hydrogen evolution reaction (HER) in both acid and base remained as a significant challenge. Herein, a novel Co nanoparticles encapsulated in nitrogen-rich carbonitride (Co@Co–N–C) electrocatalyst was fabricated via a facile approach of melamine polymerization and Co²⁺ in situ deposition and reduction. The optimized Co@Co–N–C catalyst demonstrates outstanding catalytic activity for HER in a wide range pH values. In particular, it shows ultralow onset potentials of 62 mV and 46 mV and overpotentials of 178 mV and 157 mV to achieve current density of 10 mA cm^?2 in acidic and alkaline media, respectively. Moreover, it presents outstanding electrochemical durability without degradation at all pH values. Such highly efficient electrocatalytic performance is mainly attributed to the maximum of synergistic effects between uniform dispersed Co nanoparticles and N-rich carbonitride nanotubes.     

Ultrasmall Mo2C in N-doped carbon material from bimetallic ZnMo-MOF for efficient hydrogen evolution

The exploration and development of cost-effective and highly stable electrocatalysts with the highest possible energy efficiency remain a constant pursuit in the catalyst design and synthesis for electrocatalytic hydrogen evolution reaction (HER). In this work, a convenient approach is proposed to synthesize a type of ultrafine Mo₂C nanoparticles in average sizes of 3–4 nm embedded in hierarchically porous N-doped carbon material calcined from bimetallic ZnMo-MI (MI = 2-methylimidazole) is obtained at 1000 °C, denoted as ZnMo-MI-1000. First of all, the crystalline hybrid metal-organic framework of ZnMo-MI is fabricated from zeolitic imidazolate framework of Zn-MI precursors via solvothermal reaction, in which the conversion from Zn-MI to ZnMo-MI occurs gradually over time. After calcination, the as-obtained ZnMo-MI-1000 sample shows a satisfying HER performance with the small overpotential of 83.0 mV in 0.5 M H₂SO₄ and 100.1 mV in 1.0 M KOH to reach a current density of 10 mA cm^?2, which is attributed to ultrasmall Mo₂C, Mo and N-doped graphitic carbon matrix. The multiporous network of ZnMo-MI-1000 can provide continuous mass transportation with a minimal diffusion resistance that produce effective electrocatalytic kinetics in both acidic and alkaline media, which is utilized as a highly active and durable nonprecious metal electrocatalyst for HER.     

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.     

Zeolite imidazolate framework-8 derived molybdenum carbide/nitrogen-doped carbon for highly-efficient hydrogen evolution reaction

A metal-organic framework-derived method was developed to synthesize highly efficient non-noble metal electrocatalyst for alkaline hydrogen evolution reaction (HER). Zn²⁺, phosphomolybdic acid were coordinated with 2-methylimidazole, and zinc (Zn) and phosphorus (P) species were removed by annealing at 850 °C in N₂ atmosphere, resulting in micro/mesoporous molybdenum carbide (Mo₂C) composited with nitrogen-doped carbon (denoted as ZIF8-xMo-850). The optimized sample ZIF8-12Mo-850 displayed a low overpotential of ~85.7 mV to deliver a current density of 10 mA cm⁻², with a corresponding Tafel slope of ~69.7 mV dec⁻¹ in 1 M KOH. This HER catalytic activity was competitive with the most recently developed Mo₂C-based HER electrocatalysts. From further investigation, the high HER catalytic activity of ZIF8-12Mo-850 is owing to three aspects: (i) The appropriate Mo feeding amount of ZIF8-12Mo-850 resulted in the highest surface content of Mo²⁺ active site; (ii) The evaporation of Zn and P in the ZIF8-12Mo precursor formed its largest average pore diameter of 32.3 nm, which leaded to the highest electrochemically active surface area (ECSA) of 64.29 cm² (iii) The 2-methylimidazole in the precursor resulted in the highest surface content of pyridinic N in ZIF8-12Mo-850 (14.63%), which efficiently improved its conductivity and charge transfer efficiency.     

Ru-doped 3D porous Ni3N sphere as efficient Bi-functional electrocatalysts toward urea assisted water-splitting

Developing efficient, stable and ideal urea oxide (UOR) electrocatalyst is key to produce green hydrogen in an economical way. Herein, Ru doped three dimensional (3D) porous Ni₃N spheres, with tannic acid (TA) and urea as the carbon and nitrogen resources, is synthesized via hydrothermal and low-temperature treated process (Ru–Ni₃N@NC). The porous nanostructure of Ni₃N and the nickel foam provide abundant active sites and channel during catalytic process. Moreover, Ru doping and rich defects favor to boost the reaction kinetics by optimizing the adsorption/desorption or dissociation of intermediates and reactants. The above advantages enable Ru–Ni₃N@NC to have good bifunctional catalytic performance in alkaline media. Only 43 and 270 mV overpotentials are required for hydrogen evolution (HER) and oxygen evolution (OER) reactions to drive a current of 10 mA cm^?2. Moreover, it also showed good electrocatalytic performance in neutral and alkaline seawater electrolytes for HER with 134 mV to drive 10 mA cm^?2 and 83 mV to drive 100 mA cm^?2, respectively. Remarkably, the as-designed Ru–Ni₃N@NC also owns extraordinary catalytic activity and stability toward UOR. Moreover, using the synthesized Ru–Ni₃N@NC nanomaterial as the anode and cathode of urea assisted water decomposition, a small potential of 1.41 V was required to reach 10 mA cm^?2. It can also be powered by sustainable energy sources such as wind, solar and thermal energies. In order to make better use of the earth's abundant resources, this work provides a new way to develop multi-functional green electrocatalysts.     

Self-supported N-Doped Carbon@NiXCo2-XP core-shell nanorod arrays on 3D Ni foam for boosted hydrogen evolution reaction

The development of highly efficient and low-cost electrocatalysts for large-scale hydrogen evolution reaction (HER) is great important but remains a significant challenge. Transition-metal phosphides (TMPs) have attracted intense attention as promising non-noble-metal HER electrocatalysts due to their unique electronic properties and high intrinsic catalytic activities. Herein, we directly grew Ni_XCo_2-XP nanorod wrapped with N-doped carbon shell on 3D Ni foam to fabricate a self-supported electrode with core-shell nanorod array morphology. The obtained hybrid electrode exhibits remarkable electrocatalytic HER activity over a wide pH range with low overpotentials of 121 mV and 181 mV to obtain the current density of 200 mA cm⁻² in 0.5 M H₂SO₄ and 1 M KOH electrolytes, respectively, which is comparable to that of the current state-of-the-art Pt/C electrocatalyst. The experimental results indicate that the elaborate architectural superiority and compositional synergy of this hybrid electrode give rise to the boosted HER performance.     

Directly growth of highly uniform MnS–MoS2 on carbon cloth for advanced H2 evolution electrocatalyst in different pH electrolytes

The activation energy barrier of the H–O bond of water molecules is high, and thus the rate of H₂ evolution reaction (HER) via water splitting is very slow. Hence, chemists are committed to finding high-performance, cheap and stable catalysts for realizing efficient H₂ production. The molybdenum disulfide (MoS₂)-based bimetallic sulfide electrocatalysts are favored by researchers because of their particular structures and properties. Herein, the Waugh type polyoxometalate (POM) is used as raw materials. A series of MnS–MoS₂ electrocatalysts are in-situ coupled on carbon cloth (CC) substrate by a hydrothermal sulfidation method. The catalyst MnS-MoS₂-CC possesses high catalytic activity for HER in a alkaline electrolyte, showing a low overpotential of 54 mV at a current density of 10 mA cm^?2, which is very close to 35 mV of the 20% Pt/C electrode. Meanwhile, under a current density of over 50 mA cm^?2, the overpotential of MnS-MoS₂-CC is less than that of the 20% Pt/C electrode. Moreover, the electrocatalysts show overpotentials of 141 mV and 201 mV at a current density of 10 mA cm^?2 in 0.5 M H₂SO₄ and 1.0 M phosphate buffer solution (PBS), respectively. Besides the high catalytic activity, the MnS-MoS₂-CC electrode shows long-term durability in a wide pH range, which is confirmed by several methods including the tests of linear sweep voltammetry (LSV) curve, current density vs. time (I-t) curve, and scanning electron microscopy (SEM). This work provides a feasible route for the preparation of HER electrocatalysts applied in broad pH conditions, especially for alkaline solutions.