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 MoN 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.