Efficient hydrogen evolution reaction due to topological polarization

Materials carrying topological surface states (TSS) provide a fascinating platform for the hydrogen evolution reaction (HER). Based on systematic first-principles calculations for A3B (A = Ni, Pd, Pt; B = Si, Ge, Sn), we propose that topological electric polarization characterized by the Zak phase can be crucial to designing efficient catalysts for the HER. For A3B, we show that the Zak phase takes a nontrivial value of π in the whole (111) projected Brillouin zone, which causes quantized electric polarization charges at the surface. There, depending on the adsorption sites, the hydrogen (H) atom hybridizes with the TSS rather than with the bulk states. When the hybridization has an intermediate character between the covalent and ionic bonds, the H states are localized in the energy spectrum, and the change in the Gibbs free energy (ΔG) due to the H adsorption becomes small. Namely, the interaction between the H states and the substrate becomes considerably weak, which is a highly favorable situation for the HER. Notably, we show that ΔG for Pt3Sn and Pd3Sn are just -0.066 and -0.092 eV, respectively, which are almost half of the value of Pt.