Porous cobalt/tungsten nitride polyhedra as efficient bifunctional electrocatalysts for overall water splitting

The construction of porous bifunctional electrocatalysts is highly desirable for efficient overall water splitting, which however remains a challenge. Herein, porous cobalt/tungsten nitride (Co/WN) polyhedra were successfully synthesized by the growth of a polyhedral Co-W oxide precursor on Ni foam followed by a controlled nitridation as a bifunctional electrocatalyst for high-efficiency hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The porous structure of the Co/WN polyhedra can provide more reactive sites and promote mass/charge transfer. Moreover, the synergy between Co and WN can adjust the electronic structure, thus facilitating the adsorption/desorption of intermediates on the catalyst. Due to the above advantages, the optimized Co/WN polyhedra exhibit superior bifunctional performance in alkaline electrolyte with low overpotentials of 27 and 232 mV (without iR compensation) at a current density of 10 mA cm(-2) for the HER and OER, respectively. Especially, the Co/WN-600 sample shows better performance than commercial Pt/C and RuO2 at high current densities. Furthermore, the self-supported Co/WN polyhedra enable overall water splitting at a low cell voltage of 1.51 V to obtain a current density of 10 mA cm(-2) with outstanding catalytic durability.