Stabilizing Ti3C2TxMXene flakes in air by removing confined water

Abstract

MXenes have demonstrated potential for various applications owing to their tunable surface chemistry and metallic conductivity. However, high temperatures can accelerate MXene film oxidation in air. Understanding the mechanisms of MXene oxidation at elevated temperatures, which is still limited, is critical in improving their thermal stability for high-temperature applications. Here, we demonstrate that Ti3C2Tx MXene monoflakes have exceptional thermal stability at temperatures up to 600 °C in air, while multiflakes readily oxidize in air at 300 °C. Density functional theory calculations indicate that confined water between Ti3C2Tx flakes has higher removal energy than surface water and can thus persist to higher temperatures, leading to oxidation. We demonstrate that the amount of confined water correlates with the degree of oxidation in stacked flakes. Confined water can be fully removed by vacuum annealing Ti3C2Tx films at 600 °C, resulting in substantial stability improvement in multiflake films (can withstand 600 °C in air). These findings provide fundamental insights into the kinetics of confined water and its role in Ti3C2Tx oxidation. This work enables the use of stable monoflake MXenes in high-temperature applications and provides guidelines for proper vacuum annealing of multiflake films to enhance their stability.