Big to Small: Ultrafine Mo₂ C Particles Derived from Giant Polyoxomolybdate Clusters for Hydrogen Evolution Reaction

Due to its electronic structure, similar to platinum, molybdenum carbides (Mo₂ C) hold great promise as a cost-effective catalyst platform. However, the realization of high-performance Mo₂ C catalysts is still limited because controlling their particle size and catalytic activity is challenging with current synthesis methods. Here, the synthesis of ultrafine β-Mo₂ C nanoparticles with narrow size distribution (2.5 ± 0.7 nm) and high mass loading (up to 27.5 wt%) on graphene substrate using a giant Mo-based polyoxomolybdate cluster, Mo₁₃₂ ((NH₄ )₄₂ [Mo₁₃₂ O₃₇₂ (CH₃ COO)₃₀ (H₂ O)₇₂ ]·10CH₃ COONH₄ ·300H₂ O) is demonstrated. Moreover, a nitrogen-containing polymeric binder (polyethyleneimine) is used to create MoN bonds between Mo₂ C nanoparticles and nitrogen-doped graphene layers, which significantly enhance the catalytic activity of Mo₂ C for the hydrogen evolution reaction, as is revealed by X-ray photoelectron spectroscopy and density functional theory calculations. The optimal Mo₂ C catalyst shows a large exchange current density of 1.19 mA cm^-2 , a high turnover frequency of 0.70 s^-1 as well as excellent durability. The demonstrated new strategy opens up the possibility of developing practical platinum substitutes based on Mo₂ C for various catalytic applications.