In situ oxidized Mo₂CT_x MXene film via electrochemical activation for smart electrochromic supercapacitors

Mo₂CT_x MXenes have great potential for multifunctional energy storage applications because of their outstanding electrical conductivity, superior cycling stability, and high optical transmittance. In this study, we fabricate Mo₂CT_x film electrodes (referred to as Mo₂C) on fluorine-doped tin oxide (FTO) substrates using the layer-by-layer (LbL) self-assembly technique. To improve the energy-storage performance of Mo₂CT_x film electrodes, we develop a convenient electrochemical activation process to prepare in situ oxidized Mo₂CT_x/MoO₃ film electrodes (referred to as EA-Mo₂C). The Mo₂CT_x/MoO₃ hybrid film benefits from the addition of MoO₃, which introduces extra redox sites and enhances the charge-storage capacity. Furthermore, the unique layered structure of Mo₂CT_x significantly reduces the diffusion energy barrier for cations. The synergistic interaction between Mo₂CT_x and MoO₃ results in superior electrochemical performance, and the EA-Mo₂C displays a remarkable increase in areal specific capacitance, achieving 23.29 mF cm^-2 at a current density of 1.5 mA cm^-2, which is 518 % higher than that of Mo₂C. The electrochromic supercapacitor, assembled using EA-Mo₂C as the ion-storage layer and polyaniline (PANI) as the electrochromic layer, enables power visualization and quantitative display. In summary, this study utilizes in situ electrochemical activation to derive high-performance electrode materials, offering an innovative strategy for advancing MXene-based energy-storage materials.