Nano-Cu-mediated multi-sites approach for growing ultrafine MoO2 nanoparticles on PDDA-rGO as a robust hydrogen evolution electrocatalyst.

The catalyst with high atom utilization efficiency accompanied by improved reactivity and durability is highly desired. Metallic MoO2 with small size is easy to agglomerate, making it difficult to water splitting for hydrogen by electrolysis. Here, the nano-Cu-mediated multi-sites method is proposed for the first time 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 growing sites for MoO2 on PDDA-rGO and simultaneously promotes the growing rate of MoO2 on PDDA-rGO. As a consequence, the resulting size of MoO2 NPs is only 2 nm and evenly disperse on PDDA-rGO. Significantly, the optimized catalyst possesses an onset potential low to -42 mV vs. reversible hydrogen electrode (RHE), a calculated Tafel slope only 42 mV dec-1 and good cycling stability more than 40 h. This favored hydrogen evolution reaction (HER) activity is aroused by the synergistic effect of MoO2 and PDDA-rGO, rapid charge transport and sufficient exposed active sites of MoO2/PDDA-rGO.