Engineering NiCoP/MoxC heterojunction for highly efficient hydrogen evolution reaction in alkaline and acid solution

A hybrid electrocatalyst composed of NiCoP and Mo_xC has been prepared via the two-step calcination method. Microscopic analysis demonstrates that the heterojunctions formed by the NiCoP and Mo_xC are disordered and stacked irregularly. The NiCoP/Mo_xC heterojunctions are produced during the second calcination treatment. The synergistic effects promote water adsorption and dissociation, and H₂ desorption. More active sites are provided by the irregular structure, the NiCoP/Mo_xC-X catalyst are imparted excellent electrocatalytic activity toward hydrogen evolution reaction (HER) activity. To sustain a current density of 10.0 mA/cm², the overpotentials of NiCoP/Mo_xC-15 are 79.0 and 116.0 mV while the Tafel slopes are 52.3 and 57.4 mV/dec for the electrocatalyst operated in 1.0 M KOH and 0.50 M H₂SO₄, respectively. When operating in alkaline medium for 10.0 h at an overpotential of 123.0 mV, the retaining catalytic activity of this material reaches 93.0%.     

Metal-organic framework derived Ni/Mo2C/Mo2TiC2Tx@NC as an efficient electrocatalyst for enhanced hydrogen production

Metal-organic framework's (MOF) shortcomings, such as poor conductivity, poor stability, and easy aggregation, impede its development in various application fields. Ni/Mo₂C/Mo₂TiC₂T_x@NC, a high-performance electrocatalyst for hydrogen evolution reaction, was prepared by incorporating a Mo₂TiC₂T_x MXene conductive matrix into MOF (namely C–Y). The Ni/Mo₂C/Mo₂TiC₂T_x@NC electrocatalyst demonstrates a remarkable HER ability with an overpotential of 105 and 134 mV and Tafel slope of 58 and 75 mV dec⁻¹ at a current density of 10 mA cm⁻² in 0.5 M H₂SO₄ and 1.0 M KOH, respectively. The outperformed HER activity of Ni/Mo₂C/Mo₂TiC₂T_x@NC catalyst is ascribe to the introduction of conductive Mo₂TiC₂T_x MXene as a carrier to improve the poor conductivity of MOF, the synergistic effect of Ni and Mo₂C nanoparticles, and the protective effect of the carbon layer. The work not only provides an experimental approach to address the problem of poor conductivity of MOF, but also provides a high-performance electrocatalyst for HER reactions. By utilizing MOFs and MXene as the precursor and the conducting carrier, our work provides some experimental reference for fabrication of multi-component inexpensive electrocatalysts.     

Ni modified ultrafine MoxC (x = 1, 2) wrapped by nitrogen-doped carbon for efficient hydrogen evolution reaction in acid and alkaline electrolytes

Hydrogen production is of significance in solving urgent energy and environmental issues, so it is necessary to develop superior electrocatalysts to catalyze the sustainable hydrogen evolution process efficiently. This study reports the synthesis of the Ni modified ultrafine Mo_xC (x = 1, 2) wrapped by nitrogen-doped carbon through a facile one-pot strategy, which can be applied for catalyzing the hydrogen evolution reaction (HER) in both acid and alkaline conditions. Benefiting from the regulating effect of Ni towards Mo_xC (x = 1, 2) and the synergistic mechanism among Ni, Mo₂C and MoC, Ni/Mo_xC-NC exhibits superior electrocatalytic activity, displaying a low overpotential of 141 mV in 0.5 M H₂SO₄ and 110 mV in 1 M KOH at a current density of 10 mA cm⁻² for HER, as well as long-term durability for 20 h.     

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.     

First insight on Mo(II) as electrocatalytically active species for oxygen evolution reaction

The replacement of noble metals with earth-abundant metals is still a big challenge for the practical application of electrocatalysis. In this work, we have developed the Mo_xC-modified alloy@nitrogen-doped carbon hybrid electrocatalysts (Mo_xC-alloy@NC, alloy: FeCo, NiCo) for oxygen evolution reaction (OER) by a simple thermolysis method. Compared with FeCo@NC and NiCo@NC, the OER performances of Mo_xC-FeCo@NC and MoC-NiCo@NC are greatly enhanced, mainly due to the improved electrical conductivity by the introduce of Mo_xC. Moreover, Mo_xC-FeCo@NC exhibits a smaller Tafel slope (80 mV/dec) and a lower overpotential (318 mV) at 10 mA cm⁻² in 1 M KOH solution, compared with MoC-NiCo@NC (186 mV/dec, 352 mV). In consideration of a lower BET area (6.6 m² g⁻¹) of Mo_xC-FeCo@NC than those of MoC-NiCo@NC (25.4 m² g⁻²), the remarkable electrocatalytic activity of Mo_xC-FeCo@NC is mainly attributed to the presence of Mo(II) acting as the OER active species. Although Mo as hydrogen evolution reaction (HER) active species is well known, Mo(II) as the OER active species has not been reported before.     

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.     

Facile construction of porous and heterostructured molybdenum nitride/carbide nanobelt arrays for large current hydrogen evolution reaction

The development of cost-effective, highly efficient and stable electrocatalysts for alkaline water electrolysis at a large current density has attracted considerable attention. Herein, we reported a one-dimensional (1D) porous Mo₂C/Mo₂N heterostructured electrocatalyst on carbon cloth as robust electrode for large current hydrogen evolution reaction (HER). The MoO₃ nanobelt arrays and urea were used as the metal and non-metal sources to fabricate the electrocatalyst by one-step thermal reaction. Due to the in-situ formed abundant high active interfaces and porous structure, the Mo₂C/Mo₂N electrocatalyst shows enhanced HER activity and kinetics, as exemplified by low overpotentials of 54, 73, and 96 mV at a current density of 10 mA cm^?2 and small Tafel slopes of 48, 59 and 60 mV dec^?1 in alkaline, neutral and acid media, respectively. Furthermore, the optimal Mo₂C/Mo₂N catalyst only requires a low overpotential of 290 mV to reach a large current density of 500 mA cm^?2 in alkaline media, which is superior to commercial Pt/C catalyst (368 mV) and better than those of recently reported Mo-based electrocatalysts. This work paves a facile strategy to construct highly efficient and low-cost electrocatalyst for water splitting, which could be extended to fabricate other heterostructured electrocatalyst for electrocatalysis and energy conversion.     

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.     

Facile process to utilize carbonaceous waste as a carbon source for the synthesis of low cost electrocatalyst for hydrogen production

Low cost non-noble metal electrocatalysts are highly desirable for the sustainable production of hydrogen as a renewable energy source. Molybdenum carbide (Mo₂C) has been considered as the promising non-noble metal electrocatalyst for the hydrogen production via hydrogen evolution reaction (HER) through water splitting. The nanostructured nitrogen (N) incorporated carbon (C) coupled with Mo₂C is the potential candidate to boost the HER activity and electrode material for the energy conversion applications. In this work, nitrogen incorporated carbon coated Mo₂C (Mo₂C@C/N) has been synthesized in an eco-friendly way using waste plastic as the carbon source. The pure phase Mo₂C@C/N has been synthesized at 700 and 800 °C for 10 h. The relatively higher temperature synthesized phase shows enhanced HER activity with lower Tafel slope (72.9 mVdec⁻¹) and overpotential of 186.6 mV to drive current density of 10 mAcm⁻². It also exhibits stability up to 2000 cyclic voltammetry (CV) cycles and retains the current density with negligible loss for 10 h. The higher temperature synthesized phase exhibits higher electrochemical active surface area (ECSA) and enhanced HER kinetics.     

Self-standing,hybrid three-dimensional-porous MoS2/Ni3S2 foam electrocatalyst for hydrogen evolution reaction in alkaline medium

Self-standing and hybrid MoS₂/Ni₃S₂ foam is fabricated as electrocatalyst for hydrogen evolution reaction (HER) in alkaline medium. The Ni₃S₂ foam with a unique surface morphology results from the sulfurization of Ni foam showing a truncated-hexagonal stacked sheets morphology. A simple dip coating of MoS₂ on the sulfurized Ni foam results in the formation of self-standing and hybrid electrocatalyst. The electrocatalytic HER performance was evaluated using the standard three-electrode setup in the de-aerated 1 M KOH solution. The electrocatalyst shows an overpotential of 190 mV at ?10 mA/cm² with a Tafel slope of 65.6 mV/dec. An increased surface roughness originated from the unique morphology enhances the HER performance of the electrocatalyst. A density functional approach shows that, the hybrid MoS₂/Ni₃S₂ heterostructure synergistically favors the hydrogen adsorption-desorption steps. The hybrid electrocatalyst shows an excellent stability under the HER condition for 12 h without any performance degradation.     

In-situ crystalline infiltrated Mo2C@C for efficient hydrogen evolution reaction

Molybdenum carbide (Mo₂C) is a promising electrocatalyst for hydrogen evolution reaction (HER) due to the similar electron orbital structure to platinum. Preparing Mo₂C catalyst in nanoscale increases the exposure of active catalyst site and significantly enhances electrochemical reaction and improve HER performance. However, Mo₂C is not a good electron conductor which still requires a more sufficient contact between the catalyst and electrode to transfer electron current. Here, we proposed in-situ Mo₂C growth on carbon nanotubes (CNTs) by using wet impregnation of ammonium molybdate tetrahydrate as Mo source, which established a crystalline transition contact between Mo₂C and CNTs and significantly improved HER performance. Our results further showed the optimized HER performance of Mo₂C@C_amt and achieved a lower Tafel slopes and low onset potential (η_onset) of 46.7 mV dec⁻¹, 51.3 mV dec⁻¹ and 73 mV and 127 mV (vs. RHE) under alkaline and acidic condition, respectively. Furthermore, Mo₂C@C_amt also shows less attenuation after 1000 times of cyclic voltammograms (CV) cycling stability test and 25 h continuous operation under alkaline and acidic condition.     

Heterostructured two dimensional materials of MXene and graphene by hydrothermal method for efficient hydrogen production and HER activities

Recent development on two-dimensional (2D) heterostructured graphene and MXene materials were explored for electrochemical water splitting hydrogen evolution reaction (HER) activity. The hybrid MXene/reduced graphene oxides as two-dimensional (2D) hybrid structures were prepared by facile hydrothermal techniques at 150 °C with MXene and RG hybrid layered composites. As-prepared electrocatalytic active materials have been confirmed through structural and surface morphological studies such as XRD, RAMAN, FT-IR and SEM analysis. The prepared 2D materials were carried out for HER activities due to attractive conductivity and mass transfer process. HER performance were tested from linear sweep voltammetry (LSV) cures. The prepared MX, RG and MX@RG hybrid electrocatalyst exhibited overpotential values as observed as 220 mV, 193 mV, 121 mV respectively at 10 mAcm^?2 cathodic on set. MX@RG hybrid heterostructure exhibited enhanced HER action with lowest overpotential (η = 121 mV) and good H₂ productions as an active future electrocatalyst for energy storage and conversion applications.     

Hydrothermally synthesized nickel molybdenum selenide composites as cost-effective and efficient trifunctional electrocatalysts for water splitting reactions

The development of efficient, cost-effective routes to prepare non-platinum-based electrocatalysts is a significant scientific challenge in water-splitting systems. A multifunctional electrocatalyst for the hydrogen evolution, oxygen evolution, and oxygen reduction reactions (HER/OER/ORR) involved in the water-splitting process was fabricated using a simple and eco-friendly strategy. The present study involves the simple synthesis of nanostructured nickel selenide (NiSe) via a hydrothermal method. The different phases of nickel selenide and their dependency on the precursor concentration were analyzed using X-ray diffraction (XRD). The morphologies of coral-like structured pure and Mo-doped NiSe (Ni_1-xMo_xSe) samples were investigated systematically using scanning electron microscopy (SEM). The as-prepared Ni_0.5Mo_0.5Se material showed an enhanced electrochemical activity of 1.57 V @ 10 mA/cm² for OER and 0.19 V @ 10 mA/cm² to HER, and follows the Volmer-Heyrovsky for HER mechanism. In addition, the electrocatalyst exhibits a large electrochemical surface area and high stability. Therefore, the hydrothermally synthesized Ni_1–xMo_xSe has been proven to be a perfect platinum-free trifunctional electrocatalyst for water splitting process.     

Structure and electrocatalytic hydrogen evolution performance of Mo2C thin films prepared by magnetron sputtering

Mo₂C, which has a unique electronic structure similar to the electronic structure of Pt, is considered as the material with the greatest potential to replace Pt as a catalyst for the electrocatalytic hydrogen evolution reaction (HER). However, Mo₂C thin films have not attracted enough attention in the field of electrocatalysis. This work proposes a method for preparing Mo₂C thin films as a catalyst for electrocatalytic HER through radiofrequency magnetron sputtering. The HER activity of the Mo₂C thin film in acidic and alkaline media is studied by changing the deposition power of the Mo₂C target and doping Ni for structural modification. Results show that increasing the deposition power of Mo₂C can significantly enhance the HER activity of the films in acidic and alkaline media, and metal Ni doping can further enhance the HER activity of the Mo₂C films. In an alkaline environment at a current density of 10 mA cm⁻², the films demonstrate an overpotential of as low as 163 mV with a Tafel slope of 107 mV·dec⁻¹. In acidic media, the films present the corresponding overpotential of 201 mV and a Tafel slope of as low as 96 mV·dec⁻¹. Moreover, the Ni-doped Mo₂C films have excellent HER stability. The synergy between doped Ni and Mo vacancies optimizes the strength of the Mo–H bond and the adsorption and desorption equilibrium of active H, thus enhancing HER kinetics. This work guides the possible structural design of Mo₂C thin films for electrocatalytic HER.     

Facile and rapid synthesis of Pt-NiOx/NiF composites as a highly efficient electrocatalyst for alkaline hydrogen evolution

A highly efficient and stable catalyst is the goal of practical electrolysis of water for hydrogen production. Here, Pt-NiO_x nanocomposites anchoring on Ni foam (Pt-NiO_x/NiF) is synthesized by a flexibility galvanic replacement within 2 h and manifests a considerable application prospect for hydrogen evolution reaction (HER) in alkaline media. Owing to the faster kinetics result from appropriate noncovalent interaction, Pt-NiO_x/NiF achieved respectively a factor of 12 and 1.8 enhancement in HER current density relative to NiO_x/NiF and commercial Pt/C at an overpotential of 200 mV. Moreover, such a heterogeneous electrocatalyst have demonstrated a superior long-term stability of 100 h at a high current density of 50 mA/cm². The low cost, easy scalable synthetic strategy and exceptional HER activity makes the industrial application of Pt-NiO_x/NiF possible.     

Effect of Mo content on hydrogen evolution reaction activity of Mo2C/C electrocatalysts

Recent research suggests that molybdenum carbide (β-Mo₂C) has the potential to be a cheap and active substitute for Pt-based electrocatalyst for hydrogen evolution reaction. In this article molybdenum carbide (Mo₂C) electrocatalysts immobilized on carbon support were synthesized and evaluated for hydrogen evolution reaction (HER). The quantity of Mo in the samples was varied to understand the effect of Mo content in Mo₂C/C electrocatalyst on the structure, morphology, electrochemical properties and HER. The Mo weight percentages determined by ICP-OES technique in four Mo₂C/C samples prepared were found as ~9.3, 15.8, 20.4 and 28.0. SAXS studies revealed that the pore size of the carbon increased with an increase in Mo content, most probably to accommodate the Mo₂C motifs. X-ray photoelectron spectra showed that the amount of low valent Mo increased as we increased the Mo content up to 20 wt % but decreased in the 28 wt % sample. All the samples were active for electrochemical HER with the sample having ~20 wt % Mo showing the highest activity and exhibited a Tafel slope of 69 mVdec⁻¹. Among all samples the 20 wt% Mo sample exhibited the highest electrochemical surface area (ECSA) of ~2.92 mFcm⁻² and minimum charge transfer resistance for the HER. Thus, it is concluded that 20 wt% Mo in Mo₂C/C electrocatalyst evolves with ideal pore size, highest ECSA, smooth charge transfer and thus exhibits the best electrochemical properties for HER.     

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 solution-induced impregnation synthesis of strongly coupled platinum–molybdenum/silicon carbide quantum dots heterostructures encapsulated on reduced graphene oxide sheet as electrocatalyst for hydrogen evolution reaction

Strongly coupled platinum-based transition-metal oxide/carbon hybrids and the development of quantum-dot structures of hybrid catalysts are cost-effective and maximize accessible active sites. However, a significant obstacle still exists for the rational proposal and simple synthesis of hybrid quantum-dot material catalysts. Herein, novel Pt_xMo_1-xSiC quantum dots encapsulated in reduced graphene oxide (rGO) (Pt_xMo_1-xSiC QDs @rGO) for catalyzing the hydrogen evolution reaction (HER) were fabricated through a simple solution-induced impregnation method. The optimized Pt₅Mo₉₅SiC QDs @rGO catalyst only require overpotentials of 18 mV and 25 mV to deliver current densities of 10 mA cm⁻² and 250 mA cm⁻² in acidic media, respectively. The synergistic effects of the inner Pt_xMo_1-xSiC QDs networks and outer conductive rGO sheets that promote electron transfer are responsible for the outstanding HER performance. This work presents a novel method for producing an extremely effective HER catalyst for applications on large-scale.     

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.     

Ni3S2-MoSx nanorods grown on Ni foam as high-efficient electrocatalysts for overall water splitting

In order to solve the problem of large overpotential in water electrolysis for hydrogen production, transition metal sulfides are promising bifunctional electrocatalysts for hydrogen evolution reaction/oxygen evolution reaction that can significantly reduce overpotential. In this work, Ni₃S₂ and amorphous MoS_x nanorods directly grown on Ni foam (Ni₃S₂-MoS_x/NF) were prepared via one-step solvothermal process, which were used as a high-efficient electrocatalyst for overall water splitting. The Ni₃S₂-MoS_x/NF composite exhibits very low overpotentials of 65 and 312 mV to reach 10 mA cm⁻² and 50 mA cm⁻² in 1.0 M KOH for HER and OER, respectively. Besides, it exhibits a low Tafel slope (81 mV dec⁻¹ for HER, 103 mV dec⁻¹ for OER), high exchange current density (1.51 mA cm⁻² for HER, 0.26 mA cm⁻² for OER), and remarkable long-term cycle stability. This work provides new perspective for further the development of highly effective non-noble-metal materials in the energy field.