(NixFeyCo6-x-y)Mo6C cuboids as outstanding bifunctional electrocatalysts for overall water splitting

Composition design of multi-metallic carbides generates an outstanding bifunctional catalyst, (NixFeyCo6-x-y)Mo6C, for electrolytic water splitting. [Display omitted] •Design multicomponent catalysts based on volcano plots of suitable descriptors.•Synthesize (NixFeyCo6-x-y)Mo6C as an outstanding bifunctional electrocatalyst.•Achieve an ultralow cell voltage of 1.47 V for delivery of 10 mA cm−2.•Enhance OER via synergistic effects between multiple active intermediates.•Identify Volmer-Heyrovsky route for HER via in-situ XAS study. Bifunctional multi-component electrocatalyst, (NixFeyCo6-x-y)Mo6C, developed based on volcano plots of suitable descriptors, achieves ultralow overpotentials of 20 and 194 mV for hydrogen evolution reaction (HER) and 212 and 336 mV for oxygen evolution reaction (OER) at current densities of 10 and 500 mA cm−2, respectively. When serving as both anode and cathode for overall water splitting, it requires ultralow cell voltages of only 1.47 and 1.77 V to deliver current densities of 10 and 500 mA cm−2, respectively and exhibits ultrastability, experiencing chronoamperometric decay of only 6.2 % at an ultrahigh initial current density of 500 mA cm−2 for 50 h. The outstanding OER performances may be attributed to formation of and synergistic effects between multiple active intermediates during the OER, as revealed with an in-situ Raman spectroscopic study. With an in-situ X-ray absorption spectroscopic examination, the HER is identified to proceed through the Volmer-Heyrovsky route.