Multiple-Fold Fermions and Topological Fermi Arcs Induced Catalytic Enhancement in Nanoporous Electride C12A7

TL;DR

This study reveals that multiple-fold fermions in the electride C12A7 create topological surface states with long Fermi arcs, significantly enhancing its catalytic activity, especially for hydrogen evolution reactions.

Contribution

It uncovers the role of multiple-fold fermions and topological surface states in boosting electride catalytic performance, providing a new understanding of topological quantum catalysts.

Findings

Multiple-fold fermions are present in C12A7 due to interstitial electrons.

Long Fermi arcs on the surface correlate with high catalytic activity.

Shifting Fermi arcs away from the Fermi level reduces catalytic efficiency.

Abstract

Topological materials are recently regarded as the idea catalysts due to the protected surface metallic states and high carrier mobility, however the fundamental mechanism and the underlying relationship between the catalytic performance and topological states are in debate. Here, by means of symmetry analysis and first-principles calculations, we discover that the electride material of C12A7 hosts the multiple-fold fermions due to the interstitial-electrons, with the sixfold- and fourfold- degenerate points locating at high symmetric points near the Fermi energy, which are identified as the underlying reason of the enhanced catalytic ability in C12A7-based catalysts. The multiple-fold fermions exhibit much longer Fermi arcs on the (001) surface than traditional Weyl/Dirac fermions, the surface is thus highly chemical active and possesses a low Gibbs free energy for the hydrogen evolution reaction. The underlying relationship between catalytic performance and the topological surface state is explicitly verified by artificially hole doping, external strain and similar electride without the Fermi arcs, where the Gibbs free energies are significantly increased when the Fermi arcs is shifted to higher energy level. This work offers a guiding principle for understanding catalytic nature of electrides and the topological quantum catalysts.