# Topological nodal line states and a potential catalyst of hydrogen evolution in the TiSi family

## TL;DR

This paper introduces a new topological nodal line semimetal in the TiSi family that shows promise as a catalyst for hydrogen evolution, leveraging its surface states and topological properties for efficient water splitting.

## Contribution

It reports the discovery of a TiSi-type topological nodal line semimetal with near-zero hydrogen adsorption free energy, proposing it as a novel quantum catalyst for HER based on topological surface states.

## Key findings

- TiSi family exhibits a closed Dirac nodal line in the bulk.
- Hydrogen adsorption on TiSi surfaces yields near-zero ΔG_{H*}.
- Topological charge participates in the HER process.

## Abstract

Topological nodal line (DNL) semimetals, formed by a closed loop of the inverted bands in the bulk, result in the nearly flat drumhead-like surface states with a high electronic density near the Fermi level. The high catalytic active sites associated with the high electronic densities, the good carrier mobility, and the proper thermodynamic stabilities with $\Delta G_{H^*}$$\approx$0 are currently the prerequisites to seek the alternative candidates to precious platinum for catalyzing electrochemical hydrogen (HER) production from water. Within this context, it is natural to consider whether or not the DNLs are a good candidate for the HER because its non-trivial surface states provide a robust platform to activate possibly chemical reactions. Here, through first-principles calculations we reported on a new DNL TiSi-type family with a closed Dirac nodal line consisting of the linear band crossings in the $k_y$ = 0 plane. The hydrogen adsorption on the (010) and (110) surfaces yields the $\Delta G_{H^*}$ to be almost zero. The topological charge carries have been revealed to participate in this HER. The results are highlighting that TiSi not only is a promising catalyst for the HER but also paves a new routine to design topological quantum catalyst utilizing the topological DNL-induced surface bands as active sites, rather than edge sites-, vacancy-, dopant-, strain-, or heterostructure-created active sites.