Electrochemical Stability of MXenes in Water Based on Constant Potential AIMD Simulations

MXene has been recently explored as promising electrocatalytic materials to accelerate the electrocatalytic process for hydrogen evolution, but their dynamic stability under electrochemical conditions remains elusive. Here we performed first-principle ab initio molecular dynamics calculations to reveal the electrochemical stability of Ti₂CT_x MXene in different aqueous environments. The results revealed the high vulnerability of the pure and vacancy-defected Ti₂CO₂ MXene towards water attack, leading to surface oxidation of MXene under neutral electrochemical condition that formed adsorbed oxygen species to Ti and dissociated proton in solution. The surface oxidation of Ti₂CO₂ could be prevented in the acid condition or in the neutral condition under the negative potential. Differently, the fully F- or OH-functionalized Ti₂CF₂ and Ti₂C(OH)₂ as well as the mixed functionalized Ti₂C(O_0.5OH_0.5)₂ and Ti₂CO_1.12F_0.88 are highly stable under various electrochemical conditions, which can effectively prevent close contact between water and surface Ti atoms via electronic repulsion or steric hindrance. These findings provide atomic level understanding of the aqueous stability of MXene and provide useful strategies to prevent degradation and achieve highly stable MXenes.