Optimizing hydrogen binding on Ru sites with RuCo alloy nanosheets for efficient alkaline hydrogen evolution.

Ruthenium (Ru)-based catalysts, with considerable performance and desirable cost, become highly concerned candidates to replace platinum (Pt) in alkaline hydrogen evolution reaction (HER). The hydrogen binding at Ru sites (Ru-H) is an important factor limiting the HER activity. Herein, density functional theory (DFT) simulations show that the essence of Ru-H binding energy is the strong interaction between the 4dz 2 orbital of Ru and 1s orbital of H. The charge transfer between Ru sites and substrates (Co and Ni) causes the appropriate downward shift of the 4dz 2 -band center of Ru, which results in a Gibbs free energy of 0.022 eV for H* in RuCo system, much decrease compared to 0.133 eV in pure Ru system. This theoretical prediction has been experimentally confirmed using RuCo alloy nanosheets (RuCo ANSs). They were prepared via fast co-precipitation method followed with a mild electrochemical reduction. Structure characterizations reveal that the Ru atoms are embed into Co substrate as isolated active sites with the planar symmetric and Z-direction asymmetric coordination structure, obtaining an optimal 4dz 2 modulated electronic structure. Hydrogen sensor and temperature program desorption (TPD) tests demonstrate the enhanced Ru-H interactions in RuCo ANSs than pure Ru nanoparticles. As a result, the RuCo ANSs reach an ultra-low overpotential of 10 mV at 10 mA/cm 2 and a Tafel slope of 20.6 mV/dec in 1 M KOH, outperforming that of the commercial Pt/C. This holistic work provides a new insight to promote alkaline HER by optimizing metal-H binding energy of active sites.