Scalable synthesis of hcp ruthenium-molybdenum nanoalloy as a robust bifunctional electrocatalyst for hydrogen evolution/oxidation

Abstract

The hydrogen evolution reaction (HER) is the cathodic process of water splitting, and its reverse, the hydrogen oxidation reaction (HOR), is the anodic process of an H2-O2 fuel cell; both play important roles in the development of hydrogen energy. The rational design and scalable fabrication of low-cost and efficient bifunctional catalysts for the HER/HOR are highly desirable. Herein, ultrasmall Mo-Ru nanoalloy (Mo0.5Ru3 and MoRu3) particles uniformly distributed on mesoporous carbon (MPC) were successfully synthesized by a simple method that is easy to scale up for mass production. After the incorporation of Mo atoms, the as-prepared Mo0.5Ru3 and MoRu3 nanoalloys maintain a hexagonal-close-packed crystal structure. In acidic media, Mo0.5Ru3 exhibits excellent Pt-like HER and HOR activity, as well as good stability. Density functional theory (DFT) calculations reveal that the H adsorption free energy (ΔGH*) on the Mo0.5Ru3 (0 0 1) surface (−0.09 eV) is much closer to zero than that of metallic Ru (−0.22 eV), which contributes to the enhanced catalytic activity. In alkaline media, Mo0.5Ru3 also presents outstanding HER and HOR activity, even significantly outperforming Pt/C. The DFT results confirm that optimal binding energies with H* and OH* intermediate species, and low energy barriers in the water dissociation and formation steps, efficiently accelerate the alkaline HER/HOR kinetics of Mo0.5Ru3. This study provides a new avenue for the scalable fabrication of high-efficiency bifunctional electrocatalysts for the HER and HOR in both acidic and alkaline media.