Efficient hydrogen evolution reaction due to topological polarization

TL;DR

This study demonstrates that topological electric polarization in certain materials enhances hydrogen evolution reaction efficiency by facilitating optimal hydrogen adsorption, with specific compounds showing near-ideal Gibbs free energy values.

Contribution

It reveals that topological polarization characterized by the Zak phase can be used to design more efficient HER catalysts, a novel approach in catalyst development.

Findings

Zak phase is nontrivial in $A_3 B$ compounds, leading to surface polarization.

Hydrogen hybridizes with topological surface states, reducing Gibbs free energy.

Pt$_3$Sn and Pd$_3$Sn show near-optimal $ riangle G$ for HER.

Abstract

Materials carrying topological surface states (TSS) provide a fascinating platform for the hydrogen evolution reaction (HER). Based on systematic first-principles calculations for $A_3 B$ ($A$ = 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 $A_3 B$, we show that the Zak phase takes a nontrivial value of $\pi$ in the whole (111) projected Brillouin zone, which causes quantized electric polarization charge 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 bond, the H states are localized in the energy spectrum, and the change in the Gibbs free energy ($\Delta G$) 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 $\Delta G$ for Pt$_3$Sn and Pd$_3$Sn are just -0.066 and -0.092 eV, respectively, which are almost half of the value of Pt.