Stability of Single-Atom Centers of MXenes under Anodic Polarization Conditions

Abstract

MXenes─few-layered two-dimensional transition metal carbides and nitrides─are a promising class of materials for energy conversion and storage. Only recently, it was predicted that the basal planes of MXenes reconstruct under positive bias under the formation of catalytically active single-atom centers, whose structure is reminiscent of a single-atom catalyst (SAC). In this work, we assess the stability of the SAC-like motif of MXenes under anodic polarization conditions. By combining density functional theory calculations and a Born-Haber cycle, we derive dissolution potentials and Pourbaix diagrams of 19 SAC-like motifs of M2X1O MXenes (M = Cr, Fe, Hf, Mo, Nb, Ta, Ti, V, W, Zr; X = C, N) for two different scenarios─(a) preoxygen evolution reaction (OER) conditions (U < 1.23 V vs reversible hydrogen electrode; RHE) without the formation of gaseous oxygen during demetalation of the active metal at the SAC site, and (b) OER conditions (U > 1.23 V vs RHE) by considering the formation of gaseous oxygen during demetalation at the SAC site. Our work not only provides an approach to capture the stability of archetypical SAC or SAC-like sites under electrochemical conditions but also offers theoretical guidance for the development of durable electrocatalysts for water splitting.