High valence state of Ni and Mo synergism in NiS2-MoS2 hetero-nanorods catalyst with layered surface structure for urea electrocatalysis

Abstract

High valence state species are significant in the energy-relevant electrochemical oxidation reactions. Herein, the high active state of Ni3+ formation induced by Mo6+ and their efficient synergism in NiS2-MoS2 hetero-nanorods powder catalyst with the rough layered structure are demonstrated, as proof of concept, for the urea-assisted water electrolysis. This catalyst can be derived from the sulfidation of NiMoO4 nanorods that can realize individual metal sulfides sufficiently mixing at a domain size in the nanoscale which creates lots of active sites and nanointerfaces. The high valence state of Mo6+ and Ni3+ formation and increased conductive phase of 1 T MoS2 in the hetero-nanorods compared to the counterpart pure phases are revealed by spectral study and microscopic analysis; high electrochemical surface area and active site exposure are found due to the nano-interface formation and layered rough nanosheets over the surface of nanorods. They show much higher catalytic performance than their pure phases for urea oxidation, including high catalytic activity, stability, charge transfer ability and catalytic kinetics resulting from more active Ni3+ species formation and electronic synergism of high valence metals. Transformation of 1 T MoS2 to Mo6+ and increased amount of Mo6+ and Ni3+ after stability test indicate their involvement and synergism for the catalysis reaction. The current work offers a novel understanding of the synergistic effect based on the high valence state synergism for heterogeneous catalysts in electrocatalysis.