Advances in MXene-based single-atom catalysts for electrocatalytic applications

Single-atom catalysts (SACs) possess excellent electrocatalytic activity due to their high atom utilization, unique electronic structure and unsaturated coordination environment. However, the intrinsically high surface free energy of single atoms tends to aggregate into nanoparticles or clusters during the preparation and electrocatalysis of SACs, thus endowing the attenuation of catalytic activity. Transition metal carbides/nitrides (MXene), as a new type of two-dimensional material, is an ideal carrier for fixing single atoms due to its large specific surface area, ample anchoring sites and excellent conductivity. In this review, we first summarize the advantages of MXene as a single atom carrier. Subsequently, the synthesis strategies and identification methods of MXene-based SACs are systematically explicated. Afterwards, we encapsulate the electrocatalytic mechanism of MXene-based SACs from both in situ analysis and theoretical calculations. Moreover, the electrocatalytic applications of MXene-based SACs catalysts are explored extensively, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), CO2 reduction reaction (CO2RR) and nitrogen reduction reaction (NRR). Finally, we put forward some forward-looking perspectives and future development directions, aiming to provide professional and targeted guidance for the rational design and precise preparation of highly active MXene-based SACs.