In situ electrochemical redox tuning of MXene-Co-MOF to MXene/TiO2@Co3O4 nanosheet with enhanced activity and stability

Supercapacitors have witnessed significant development in recent years due to their high power density, fast charging rate, and excellent cycle stability, which can be used in wearable devices, electric wheel loader, and other energy storage systems for needing high discharge rate. Designing a simple synthetic protocol to simultaneously produce electrode materials with high activity and stability is a significant challenge for high-performance supercapacitors. Herein, we developed an one-step in situ electrochemical oxidation method to develop MXene/TiO₂@Co₃O₄ nanosheets at room temperature and neutral solution from their corresponding MXene-Co-MOF. The dual role of in-situ electrochemical oxidation reaction was presented: (1) the electrochemical oxidation reaction facilitates the decomposition of Co₃(HHTP)₂ MOF to Co₃O₄ and the transformation of the part of MXene to TiO₂; (2) the electrochemical oxidation reaction enhances the Faradaic activity of electrode materials by forming more active sites on weak crystalline MXene/TiO₂@Co₃O₄. The electrochemically tuned MXene/TiO₂@Co₃O₄ nanosheets grown directly on the Ni foam electrodes exhibit high specific capacitance of up to 2403 F g⁻¹ at current density of 1 A g⁻¹. When assembled into an asymmetric supercapacitors (ASC) device, the MXene/TiO₂@Co₃O₄//AC device obtains a high energy density of 55.8 Wh kg⁻¹ at a power density of 799.7 W kg⁻¹ and appears 78.6% retention after 5000 cycles stability test. The improved activities are attributed to the introduction of oxygen vacancies, more active sites with poor-crystalline phase. This work provides a promising in situ electrochemistry strategy to develop electrode materials alternatives for supercapacitor applications.