Origin of surface reconstruction via oxygen termination and improved hydrogen evolution reactions in MXenes

Abstract

Aspects of the catalyst surface, including the active sites and the presence of surface termination groups and their distribution, influence the overall catalytic activity. Surface reconstruction of the catalyst modulates catalytically active sites, and the availability of these active sites affects the catalytic performance. The present work explores materials from the 2D class known as MXenes for catalytic activity using density functional theory. We systematically determined the equilibrium coverage of the termination group over the MXene surface using the Monte Carlo simulation and cluster expansion method by considering various adsorbate–adsorbate interactions of the termination groups. To identify the origin of the equilibrium coverage and understand its behaviour, the adsorbate–adsorbate interaction was further detailed to its fundamental subcomponents. To understand the effect of termination group coverage, hydrogen evolution reactions (HERs) were studied over pristine, fully terminated surface and surface with equilibrium coverage. We also incorporated the various factors that affect the HER activity, such as the type and placement of termination groups and different stacking configurations of MXenes. It was observed that the stacking configuration, type of surface termination groups, their distribution over the MXene surface, and their equilibrium coverage were the key factors that controlled the HER activity of MXenes.