Nano-Cu-Mediated Multi-Site Approach to Ultrafine MoO2 Nanoparticles on Poly(diallyldimethylammonium chloride)-Decorated Reduced Graphene Oxide for Hydrogen Evolution Electrocatalysis.

Catalysts with high atom utilization efficiency accompanied by improved reactivity and durability are highly desired. Metallic MoO2 with its small size easily agglomerates, making it difficult to use in water splitting to obtain hydrogen by electrolysis. Here, the nano-Cu-mediated multi-site method is proposed to prepare ultrafine MoO2 nanoparticles (NPs) dispersed on poly(diallyldimethylammonium chloride)-decorated reduced graphene oxide (denoted as MoO2 /PDDA-rGO). The introduction of Cu NPs increases the number of growth sites for MoO2 on the PDDA-rGO and simultaneously promotes the growth rate of MoO2 on PDDA-rGO. As a consequence, the resulting size of the MoO2 NPs is only 2 nm and these are evenly dispersed on PDDA-rGO. Significantly, the optimized catalyst has a low onset potential of -42 mV versus reversible hydrogen electrode (RHE), a calculated Tafel slope of only 42 mV dec-1 , and good cycling stability of more than 40 h. This favored hydrogen evolution reaction (HER) activity is caused by the synergistic effects of MoO2 and PDDA-rGO, rapid charge transport, and sufficient exposed active sites of MoO2 /PDDA-rGO.