Termination-Property Coupling via Reversible Oxygen Functionalization of MXenes

[Image: see text] MXenes are a growing family of 2D transition-metal carbides and nitrides, which display excellent performance in myriad of applications. Theoretical calculations suggest that manipulation of the MXene surface termination (such as =O or −F) could strongly alter their functional properties; however, experimental control of the MXene surface termination is still in the developmental stage. Here, we demonstrate that annealing MXenes in an Ar + O(2) low-power plasma results in increased =O functionalization with minimal formation of secondary phases. We apply this method to two MXenes, Ti(2)CT(x) and Mo(2)TiC(2)T(x) (T(x) represents the mixed surface termination), and show that in both cases, the increased =O content increases the electrical resistance and decreases the surface transition-metal’s electron count. For Mo(2)TiC(2)O(x), we show that the O content can be reversibly altered through successive vacuum and plasma annealing. This work provides an effective way to tune MXene surface functionalization, which may unlock exciting surface-dependent properties.