Trends in competing oxygen and chlorine evolution reactions over electrochemically formed single-atom centers of MXenes†

Abstract

Single-atom catalysts (SACs) have garnered widespread attention in the catalysis community due to their ability to catalyze transformations relevant to energy conversion and storage with high activity and selectivity and maximum atomic efficiency. Although considerable efforts are being made to develop synthetic routes for SACs based on non-noble metal atoms, the state-of-the-art SACs are largely based on rare Pt-group metals. MXenes, a new class of two-dimensional materials, offer the exciting possibility of synthesizing single-atom centers with structural similarity to archetypical SACs and without the need for scarce metal atoms such as Pt or Ir. Instead of a dedicated synthetic protocol, only a sufficiently large anodic electrode potential is required to enable the activation of the MXene basal plane by surface oxidation, and the as-formed single-atom centers are sufficiently stable under anodic bias. The electrochemically formed single-atom centers of MXenes based on surface reconstruction differ significantly from previous studies based on SAC sites obtained by doping with foreign metal atoms. In the present work, we demonstrate that the in situ formed single-atom centers of MXenes can be effectively used to catalyze energy conversion processes relevant to the chemical industry. By combining electronic structure theory calculations and descriptor-based analysis, we determine activity and selectivity trends in competing oxygen and chlorine evolution reactions and derive activity and selectivity trends for a noble metal-free electrochemical synthesis of gaseous chlorine. Our results indicate that electrochemically formed single-atom centers of two-dimensional materials can play a crucial role for the development of next-generation catalysts for sustainable energy.