Rational design of NiCo2S4 nanowire arrays on nickle foam as highly efficient and durable electrocatalysts toward urea electrooxidation

A 3D NiCo2S4 nanowire arrays directly grown on Ni foam electrode (NiCo2S4/NF) is prepared by two-step simple hydrothermal process. The morphology and phase composition of NiCo2S4/NF are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). As expected, in the following electrocatalytic measurement, the binder-free, self-made NiCo2S4/NF electrode exhibits much higher catalytic activity, lower onset potential, better stability and greater tolerance towards urea electrooxidation compared with the Ni3S2/NF electrode synthesized under the same reaction conditions. The NiCo2S4/NF electrode delivers a current density of 720 mA cm(-2) at 0.18 V (vs. Ag/AgCl) in a solution containing 5 mol L-1 KOH and 0.33 mol L-1 urea. The impressive electrocatalytic activity of the NiCo2S4/NF catalyst is largely ascribed to its distinctive structure, which exposes more electrochemical active sites at the electrode-electrolyte interface. Besides, the high intrinsic electronic conductivity also largely boosts the charge transfer rates for urea electrooxidation. The results demonstrate that the NiCo2S4/NF electrode showing a beneficial application prospect in the wastewater treatment and direct urea fuel cells.