Hydrogen Adsorption on Solid and Liquid Surfaces of Ga–Sn and Ga–In

Abstract

Dynamic liquid metal catalysts have remarkable activity and selectivity toward certain reactions, such as carbon dioxide reduction. The surface hydrogen coverage may play a role in this, including controlling competing reactions such as hydrogen evolution. Using a novel method of statistically selecting relevant snapshots from a dynamic liquid metal trajectory, the hydrogen adsorption energy is reported across liquid surfaces of Ga–Sn and Ga–In via density functional theory. A fully dynamic sampling of hydrogen adsorption to the liquid metal is also conducted with ab initio molecular dynamics at temperature. The results indicate that hydrogen only associates weakly with Ga–Sn and Ga–In surfaces, with minimal difference between the two materials. Hydrogen adsorbs only slightly more stably (≈0.1 eV) to the liquid surfaces compared to the solid. A low hydrogen coverage is predicted on the liquid metal of ≈0.03 H Å−2 at potentials of around –1.15 V (vs RHE). However, the mobility of hydrogen on the liquid surface is much greater due to a novel mechanism whereby the dynamic surface rearranges, opening pathways for diffusion. The results suggest that the unique catalytic behavior of these liquid metal materials may be due to changes in adsorbate diffusivity when the metals are melted.