Self-supporting Atmosphere-Assisted Synthesis of 1D Mo2 C-based Catalyst for Efficient Hydrogen Evolution

One-dimensional materials exhibit fascinating properties in electrocatalytic applications but their fabrication faces the challenge of tedious and complicated operations. We have developed a bottom-up strategy to construct a 1D metal carbide catalyst (Mo₂ C@NC) consisting of ultrafine Mo₂ C nanoparticles embedded within nitrogen-doped carbon layers by simply calcining a mixture of ammonium molybdate, urea and melamine. Experimental results and thermodynamic calculations demonstrate that the retainable pyrolysis-generated self-supporting atmosphere plays a crucial role in the crystalline phase and morphology of materials. When functioned as an electrocatalyst for the hydrogen evolution reaction (HER), the achieved Mo₂ C@NC presents an excellent catalytic activity as well as outstanding stability. This work could shed fresh light onto the facile synthesis of effective HER catalysts with 1D nanostructure.

Porous Molybdenum Carbide Nanostructures Synthesized on Carbon Cloth by CVD for Efficient Hydrogen Production

Molybdenum carbide (Mo₂ C) is a promising noble-metal-free electrocatalyst for the hydrogen evolution reaction (HER), due to its structural and electronic merits, such as high conductivity, metallic band states and wide pH applicability. Here, a simple CVD process was developed for synthesis of a Mo₂ C on carbon cloth (Mo₂ C@CC) electrode with carbon cloth as carbon source and MoO₃ as the Mo precursor. XRD, Raman, XPS and SEM results of Mo₂ C@CC with different amounts of MoO₃ and growth temperatures suggested a two-step synthetic mechanism, and porous Mo₂ C nanostructures were obtained on carbon cloth with 50 mg MoO₃ at 850 °C (Mo₂ C-850(50)). With the merits of unique porous nanostructures, a low overpotential of 72 mV at current density of 10 mA cm^-2 and a small Tafel slope of 52.8 mV dec^-1 was achieved for Mo₂ C-850(50) in 1.0 m KOH. The dual role of carbon cloth as electrode and carbon source resulted into intimate adhesion of Mo₂ C on carbon cloth, offering fast electron transfer at the interface. Cyclic voltammetry measurements for 5000 cycles revealed that Mo₂ C@CC had excellent electrochemical stability. This work provides a novel strategy for synthesizing Mo₂ C and other efficient carbide electrocatalysts for HER and other applications, such as supercapacitors and lithium-ion batteries.

Structural Design and Electronic Modulation of Transition-Metal-Carbide Electrocatalysts toward Efficient Hydrogen Evolution

As the key of hydrogen economy, electrocatalytic hydrogen evolution reactions (HERs) depend on the availability of cost-efficient electrocatalysts. Over the past years, there is a rapid rise in noble-metal-free electrocatalysts. Among them, transition metal carbides (TMCs) are highlighted due to their structural and electronic merits, e.g., high conductivity, metallic band states, tunable surface/bulk architectures, etc. Herein, representative efforts and progress made on TMCs are comprehensively reviewed, focusing on the noble-metal-like electronic configuration and the relevant structural/electronic modulation. Briefly, specific nanostructures and carbon-based hybrids are introduced to increase active-site abundance and to promote mass transportation, and heteroatom doping and heterointerface engineering are encouraged to optimize the chemical configurations of active sites toward intrinsically boosted HER kinetics. Finally, a perspective on the future development of TMC electrocatalysts is offered. The overall aim is to shed some light on the exploration of emerging materials in energy chemistry.

Influence of Transition Metal on the Hydrogen Evolution Reaction over Nano-Molybdenum-Carbide Catalyst

The highly efficient electrochemical hydrogen evolution reaction (HER) provides a promising way to solve energy and environment problems. In this work, various transition metals (Fe, Co, Ni, Cu, Ag, and Pt) were selected to support on molybdenum carbides by a simple organic-inorganic precursor carburization process. X-ray diffraction (XRD) analysis results indicated that the β-Mo2C phase was formed in all metal-doped samples. X-ray photoelectron spectroscopy analysis indicated that the binding energy of Mo2+ species (Mo2C) shifted to a lower value after metal was doped on the molybdenum carbide surface. Comparing with pure β-Mo2C, the electrocatalytic activity for HER was improved by transition metal doping on the surface. Remarkably, the catalytic activity improvement was more obvious when Pt was doped on molybdenum carbide (2% Pt-Mo2C). The 2% Pt-Mo2C required a η10 of 79 mV, and outperformed that of pure β-Mo2C (η10 = 410 mV) and other transition metal doped molybdenum carbides, with a small Tafel slope (55 mV/dec) and a low onset overpotential (32 mV) in 0.5 M H2SO4. Also, the 2% Pt-Mo2C catalyst demonstrated a high stability for the HER in 0.5 M H2SO4. This work highlights a feasible strategy to explore efficient electrocatalysts with low cost via engineering on the composition and nanostructure.

In situ synthesis of molybdenum carbide/N-doped carbon hybrids as an efficient hydrogen-evolution electrocatalyst

The development of non-precious metal based electrocatalysts for the hydrogen evolution reaction (HER) has received more and more attention over recent years owing to energy and environmental issues, and Mo based materials have been explored as a promising candidate. In this work, molybdenum carbide/N-doped carbon hybrids (Mo₂C@NC) were synthesized facilely via one-step high-temperature pyrolysis by adjusting the mass ratio of urea and ammonium molybdate. The Mo₂C@NC consisted of ultrasmall nanoparticles encapsulated by N-doped carbon, which had high specific surface area. They all exhibited efficient HER activity, and the Mo₂C@NC with a mass ratio of 160 (Mo₂C@NC-160) showed the best HER activity, with a low overpotential of 90 mV to reach 10 mA cm⁻² and a small Tafel slope of 50 mV dec⁻¹, which was one of the most active reported Mo₂C-based electrocatalysts. The excellent HER activity of Mo₂C@NC-160 was attributed to the following features: (1) the highly dispersed ultrasmall Mo₂C nanoparticles, which exhibited high electrochemically active surface areas; (2) the synergistic effect of the N-doped carbon shell/matrix, which facilitated the electron transport.

The molybdenum carbide/N-doped carbon hybrids (Mo₂C@NC) were synthesized facilely via one-step high-temperature pyrolysis, which exhibited efficient electrocatalytic hydrogen evolution performance.