Big to Small: Ultrafine Mo ₂ C Particles Derived from Giant Polyoxomolybdate Clusters for Hydrogen Evolution Reaction

Due to its electronic structure, similar to platinum, molybdenum carbides (Mo ₂ C) hold great promise as a cost-effective catalyst platform. However, the realization of high-performance Mo ₂ 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-Mo ₂ 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, Mo ₁₃₂ ((NH ₄ ) ₄₂ [Mo ₁₃₂ O ₃₇₂ (CH ₃ COO) ₃₀ (H ₂ O) ₇₂ ]·10CH ₃ COONH ₄ ·300H ₂ O) is demonstrated. Moreover, a nitrogen-containing polymeric binder (polyethyleneimine) is used to create MoN bonds between Mo ₂ C nanoparticles and nitrogen-doped graphene layers, which significantly enhance the catalytic activity of Mo ₂ C for the hydrogen evolution reaction, as is revealed by X-ray photoelectron spectroscopy and density functional theory calculations. The optimal Mo ₂ 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 Mo ₂ C for various catalytic applications.