Transition metal-doped ultrathin RuO2 networked nanowires for efficient overall water splitting across a broad pH range

Abstract

Although water splitting has been successfully achieved in recent years, the design of highly efficient bifunctional catalysts applicable across a broad pH range, especially in harsh acidic conditions, remains full of challenges. Here, we report a general strategy to create transition metal-doped ultrathin RuO2 nanowires (M-doped RuO2 NWs, M = Fe/Co/Ni) featuring a networked structure, a high density of defects and grain boundaries, as superior water splitting catalysts over a broad pH range. The detailed electrocatalytic results reveal that the M-doped RuO2 NWs exhibit a volcano-like electrocatalytic performance as a function of the transition metal doped. The optimized Co-doped RuO2 NWs exhibit superior oxygen evolution reaction activity with an overpotential of 200 mV to generate a current density of 10 mA cm−2 under acidic conditions, while the Ni-doped RuO2 NWs show robust hydrogen evolution reaction activity with an overpotential of 52 mV in an alkaline environment. First-principles calculations show that these distinct electrocatalytic performances can be attributed to the balanced adsorption free energy of the intermediates triggered by modulation of d-band center theory after transition metal doping. Significantly, the M-doped RuO2 NWs are further demonstrated as the best catalysts for overall water splitting with superior activities and excellent stabilities under universal pH conditions, and the optimized Co-doped RuO2 NWs‖Ni-doped RuO2 NWs deliver a very low potential of 1.537 V and a small Tafel slope of 58.2 mV dec−1 under acidic conditions, which are much lower values than those of the commercial Ir/C‖Pt/C system (1.642 mV and 80.2 mV dec−1). We have therefore demonstrated an unprecedented class of electrocatalysts with excellent performances for electrochemical water splitting across a broad pH range.