Mo2C-Based Ceramic Electrode with High Stability and Catalytic Activity for Hydrogen Evolution Reaction at High Current Density

Developing robust electrodes with high catalytic performance is a key step for expanding practical HER (hydrogen evolution reaction) applications. This paper reports on novel porous Mo2C-based ceramics with oriented finger-like holes directly used as self-supported HER electrodes. Due to the suitable MoO3 sintering additive, high-strength (55 ± 6 MPa) ceramic substrates and a highly active catalytic layer are produced in one step. The in situ reaction between MoO3 and Mo2C enabled the introduction of O in the Mo2C crystal lattice and the formation of Mo2C(O)/MoO2 heterostructures. The optimal Mo2C-based electrode displayed an overpotential of 333 and 212 mV at 70 °C under a high current intensity of 1500 mA cm-2 in 0.5 m H2SO4 and 1.0 m KOH, respectively, which are markedly better than the performance of Pt wire electrode; furthermore, its price is three orders of magnitude lower than Pt. The chronopotentiometric curves recorded in the 50 - 1500 mA cm-2 range, confirmed its excellent long-term stability in acidic and alkaline media for more than 260 h. Density functional theory (DFT) calculations showed that the Mo2C(O)/MoO2 heterostructures has an optimum electronic structure with appropriate *H adsorption-free energy in an acidic medium and minimum water dissociation energy barrier in an alkaline medium.

Recent Tendency on Transition-Metal Phosphide Electrocatalysts for the Hydrogen Evolution Reaction in Alkaline Media

Hydrogen energy is regarded as an auspicious future substitute to replace fossil fuels, due to its environmentally friendly characteristics and high energy density. In the pursuit of clean hydrogen production, there has been a significant focus on the advancement of effective electrocatalysts for the process of water splitting. Although noble metals like Pt, Ru, Pd and Ir are superb electrocatalysts for the hydrogen evolution reaction (HER), they have limitations for large-scale applications, mainly high cost and low abundance. As a result, non-precious transition metals have emerged as promising candidates to replace their more expensive counterparts in various applications. This review focuses on recently developed transition metal phosphides (TMPs) electrocatalysts for the HER in alkaline media due to the cooperative effect between the phosphorus and transition metals. Finally, we discuss the challenges of TMPs for HER.

Carbonaceous FexP Synthesized via Carbothermic Reduction of Dephosphorization Slag as Hydrogen Evolution Catalyst for Water Splitting

Developing the high-efficiency and cheap non-noble catalysts towards hydrogen evolution reaction (HER) is of significance for water splitting. Herein, for the first time, we report a simple method of acid leaching combined with carbothermic reduction with dephosphorization slag to construct a carbonaceous FexP/C catalyst. In alkaline medium, the corresponding overpotential when the output current density was 10 mA cm−2 (η10) was only 145 mV. Additionally, there was no obvious attenuation after 3000 cycles, which showed significantly better activity and stability than that of non-carbonaceous FexP catalysts prepared by gas–solid phosphating. The structure and composition of FexP/C were characterized by X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy, and inductively coupled plasma atomic emission spectrometer. The electrochemical properties of the electrode were evaluated by cyclic voltammetry, linear scanning voltammetry, electrochemical impedance spectroscopy, and cyclic stability. The results showed that the prepared FexP/C was composed of FeP-Fe2P mixed nanocrystals supported on amorphous carbon. Compared with FexP, the synergistic catalysis of the FeP and Fe2P phases as well as the interactive support effect between the FeP-Fe2P mixed nanocrystals and the amorphous carbon support will attribute the rich active sites for electrocatalytic reaction and reduce the charge transfer resistance. Thus, FexP/C has good hydrogen evolution activity and stability. Overall, the preparation of catalysts with high additional value based on dephosphorization slag was preliminarily explored.

NH4F-Induced Morphology Control of CoP Nanostructures to Enhance the Hydrogen Evolution Reaction

Developing non-noble metal catalysts with superior catalytic activity and excellent durability is critically essential to promote electrochemical water splitting for hydrogen production. Morphology control as a promising and effective strategy is widely implemented to change the surface atomic coordination and thus enhance the intrinsic catalytic performance of current electrocatalysts. Herein, a series of cobalt phosphide (CoP) electrocatalysts with tunable morphologies of nanosheets, nanowires, nanorods, and nanoblocks have been prepared for the enhanced hydrogen evolution reaction (HER) by only adjusting the amount of ammonium fluoride (NH₄F) in the hydrothermal process. Benefiting from the large active area, high surface activity, and favorable ion and gas diffusion channels, the clustered CoP nanorods obtained at a concentration of 0.15 M NH₄F show the best HER performance with only an overpotential of 71 mV at a current density of 10 mA cm^-2 and a low Tafel slope of 60.75 mV dec^-1 in 1 M KOH. After 3000 CV cycles and 24 h durability tests, there is only a very slight degradation of performance owing to its outstanding stability and robust substrate adhesion.