Oxidation of Molybdenum-Based Single-Metallic/bimetallic Carbide MXenes in Aqueous Suspensions: Mechanistic Insights

Molybdenum carbide MXenes have garnered considerable attention in electronics, energy storage, and catalysis. However, they are prone to oxidative degradation, but the associated mechanisms have not been systematically explored. Therefore, the oxidation mechanisms of Mo-based single-metallic/bimetallic carbide MXenes including Mo₂CT_x, Mo₂TiC₂T_x, and Mo₂Ti₂C₃T_x in aqueous suspensions were investigated for the first time in this study. Similar to Ti₃C₂T_x MXene, Mo-based MXenes were found to undergo oxidative degradation in their aqueous dispersions, leading to the disruption of their crystal structure and subsequent loss of optical and electronic properties. Notably, the Mo₂CT_x MXene deviated from this typical oxidation behavior as it produced an amorphous product with Mo ions instead of highly crystalline Mo-oxides during oxidation. Similarly, the Mo₂TiC₂T_x and Mo₂Ti₂C₃T_x MXenes did not yield crystalline Mo-oxides; instead, they produced highly crystalline anatase TiO₂ and a Mo-ion-containing amorphous product simultaneously. Furthermore, high-temperature annealing of the oxidized Mo₂CT_x MXene powder at 800 °C transformed the amorphous Mo-containing product into highly crystalline MoO₂ crystals. These findings highlight the unconventional oxidation behavior of Mo-based MXenes, which suggests that the formation of crystalline Mo-based oxides requires a higher activation energy during oxidation than that of TiO₂. The unique oxidative pathway reported herein can help elucidate the oxidation mechanisms of Mo-based MXene dispersions and their products. The insights from this study can pave the way for fundamental studies in academia as well as broaden the applications of Mo-based MXenes in various industries.