MOF-derived ultrasmall Ru@RuO2 heterostructures as bifunctional and pH-universal electrocatalysts for 0.79 V asymmetric amphoteric overall water splitting

Abstract

Developing heterostructures in nano-electrocatalyst has been demonstrated as a feasible method to enhance electrocatalytic activities for water splitting, since it still remains a grand challenge to develop highly efficient and stable electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) within a wide pH range. Herein, we report a facile pyrolysis strategy of Ru-MOF for rationally constructing ultrasmall Ru@RuO2 heterostructures, which exhibit extremely remarkable electrocatalytic performance toward both HER and OER in pH-universal electrolytes. Impressively, optimal Ru@RuO2-250 achieves ultralow overpotentials for both OER (198 mV, 263 mV and 182 mV @ 10 mA cm−2 in acidic, neutral and alkaline media) and HER (31 mV, 43 mV and 32 mV @ 10 mA cm−2 in acidic, neutral and alkaline media) due to the full exposure of highly active sites, which are derived from the synergism of abundant heterointerfaces, ultrafine heterostructure size and hierarchical porous structure with high surface area. Theoretical calculations reveal the charge rearrangement and electron conduction intensification near Ru-RuO2 heterointerfaces, the electronic structure changes of the active sites optimize the adsorption behavior toward various reaction intermediates, reducing the activation barriers and speeding up the reaction kinetics. Deservedly, an asymmetric-electrolyte electrolyzer employed with Ru@RuO2-250 is assembled to acquire an ultralow applied voltage of 0.79 V at 10 mA cm−2 based on amphoteric water electrolysis (HER in acidic electrolyte while OER in alkaline electrolyte).