Traditional NiCo2S4 Phase with Porous Nanosheets Array Topology on Carbon Cloth: A Flexible, Versatile and Fabulous Electrocatalyst for Overall Water and Urea Electrolysis

We report on our recent finding here that bimetallic nickel-cobalt sulfide nanosheet arrays on carbon cloth (NiCo2S4 NS/CC) by anion exchange from its NiCo-precursor could act as a flexible, versatile and fabulous electrocatalyst for both the overall water splitting and urea electrolysis in base. The overall water-splitting efficiency of this material is higher than that for reported NiCo2S4 nanowire array on CC with just needing a voltage of 1.66 V to afford 10 mA cm(-2). Moreover, this material also shows fabulous catalytic activity and selectivity for urea oxidation reaction (UOR) with an ultralow potential of 0.249 V vs SCE to obtain 10 mA cm(-2), surpassing all reported transition-metal based UOR catalysts. An urea-assisted energy-saving alkaline hydrogen-production system was further built here by replacing anodic oxygen evolution reaction with UOR. This whole urea electrolysis cell driven by NiCo2S4 NS/CC (+,-) affords 10 mA cm(-2) at a relative low voltage of 1.49 V, which is 210 mV less than that for urea-free counterpart and also comparable to those for other reported catalysts. The amazing catalytic performances should be due to the intrinsic high activity and metallic feature of NiCo2S4 phase, the nanoporous and open-shelled nanosheet topology that exposes more catalytic active sites and accelerates the diffusion of electrolyte and the generated gas bubbles, as well as the spinel structure and mixed valence states of Ni and Co elements in NiCo2S4 phase that offers richer redox reactions.