Ultrafine Molybdenum Carbide Nanocrystals Confined in Carbon Foams via a Colloid-Confinement Route for Efficient Hydrogen Production

Precise size-controlled synthesis and multiscale assembly of ultrafine non-noble-metal-based catalysts play a key role in electrochemical energy conversion. Herein, a novel colloid-confinement strategy for facile synthesis of ultrafine molybdenum carbide nanocrystals with sub-2 nm average size assembled in carbon foams (uf-Mo₂C/CF) is reported. First, uniformly sized colloidal SiO₂ nanospheres are chosen to confine the metal source (NH₄)₆Mo₇O₂₄ molecules and the glucose is as carbon source. Subsequently, by a high temperature reduction–carbonization, Mo₂C nanocrystals are achieved and uniformly assembled on the in situ formed amorphous carbon foams. The as formed uf-Mo₂C/CF demonstrates superior hydrogen evolution activity and outstanding stability in the whole pH range. These results indicate the validity of size control and multiscale structural assembly of metal carbide nanocrystals by consideration of the overall mass transport, accessibility, and quantity, as well as the capability of the active sites toward efficient electrocatalytic hydrogen evolution reaction. This strategy can also be expanded to other energy-related application.