Nano-Cu-Mediated Multi-Site Approach to Ultrafine MoO₂ Nanoparticles on Poly(diallyldimethylammonium...

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.