Graphene composites with Ru-RuO2 heterostructures: Highly efficient Mott–Schottky-type electrocatalysts for pH-universal water splitting and flexible zinc–air batteries

Development of high-efficiency electrocatalysts for pH-universal overall water splitting is a critical step towards a sustainable hydrogen economy. Herein, graphene nanocomposites with Ru-RuO2 Mott-Schottky heterojunctions (Ru-RuO2@NPC) are prepared pyrolytically and exhibit a remarkable electrocatalytic activity at pH = 0–14 towards both oxygen/hydrogen evolution reactions and overall water splitting, as compared to commercial RuO2 and Pt/C. Ru-RuO2@NPC can also be used as an effective air cathode catalyst for flexible, rechargeable zinc-air batteries. Density functional theory calculations show that the formation of Ru-RuO2 heterojunctions moderately enhances the surface charge density of metallic Ru and brings the d states closer to Fermi level, as compared to that of RuO2 alone, leading to improved intrinsic electrocatalytic activity towards these important reactions. These results demonstrate the significance of Mott-Schottky heterojunctions in the development of high-efficiency electrocatalysts for various new energy technologies.