Stress-mediated copper-molybdenum alloy enables boosted hydrogen evolution activity

Abstract

Guided by the Sabatier volcano principle, we designed a severe plastic deformation-based strategy to obtain high-performance metallic electrocatalysts with boosted hydrogen evolution activity. Cu-Mo system was selected due to their opposite Gibbs free energies of adsorbed hydrogen and surface mechanical treatment was utilized to fine-tune the adsorption energy. A surface compressive stress layer with high values of -464±37 MPa was realized under the cryogenic severe plastic deformation process. The treated metallic catalysts exhibit ultra-low overpotential (79±3 mV at 10 mA cm^-2 at the alkaline condition and 31±2 mV at 10 mA cm^-2 at the acidic condition). The effective Tafel slope of acidic hydrogen evolution treated in the cryogenic environment is 141.2 mV decade^-1, showing a fast Tafel-dominated Volmer-Tafel reaction mechanism. The density function theory calculation showed a transformation of the hydrogen adsorption site with increased external compressive stress, which contributed to the adsorption site adjacent to the supersaturated solid solution Mo atom. Bader charge analyses showed that the Mo atom lost more electrons, causing the surrounding Cu atoms to enter a stronger electronegative state, which significantly enhanced the adsorption capacity of Cu atoms for hydrogen with near-zero adsorption energy.