High-throughput theoretical optimization of the hydrogen evolution reaction on MXenes by transition metal modification

Electrocatalysis has the potential to become a more sustainable approach to generate hydrogen as a clean energy source and chemical feedstock. Finding a stable, eco-friendly, low cost and highly efficient catalyst is one of the prerequisites to realize large-scale industrial electrocatalytic hydrogen production. Two-dimensional metal carbide and nitride (MXene) materials have shown characteristics of promising hydrogen evolution reaction (HER) catalysts, but challenges in terms of both hydrogen adsorption strength and reaction rate still need to be addressed. In addition, previous theoretical studies of MXenes for the HER focus mainly on the thermodynamics (e.g. hydrogen adsorption energy) rather than the kinetics of the reaction (e.g. energy barrier and reaction rate). In this work, we utilize high-throughput computational methods to study both the HER thermodynamics and kinetics of M2XO2 type MXenes and how their HER activity can be enhanced by the modification of different transition metal (TM) adatoms. Compared to the relatively weak HER activity observed for the majority of pristine MXenes, the addition of TM adatoms on the MXene surface is predicted to enhance their HER activity significantly. The presence of TM not only optimizes the Gibbs free energy of hydrogen adsorption (DGH) but also reduces the H-2 production activation barrier. Intriguingly, we observed a HER mechanism preference switch from Volmer-Heyrovsky observed on pristine MXenes to Volmer-Tafel after modification with TM adatoms. On the basis of in-depth and systematic exploration of the electronic structure and interaction between hydrogen and MXenes, the origin of the mechanism preference switch is linked to the TM-induced electron redistribution on the surface of the MXene.