High-Power Energy Storage and Stability of Ti3C2Tx MXene at Extreme Temperatures

Pseudocapacitors have the potential to achieve high energy and high power density simultaneously, a holy grail for electrochemical energy storage. MXene-based pseudocapacitors achieve higher energy and power densities than carbon-based supercapacitors, but their electrochemical stability and degradation mechanisms under extreme temperatures remain underexplored, limiting their widespread application. Herein, we show that Ti ₃ C ₂ T _x MXene electrodes exhibit excellent rate capability in 5 M H ₂ SO ₄ electrolyte from − 40°C to 100°C, delivering 700 F cm ^− 3 (200 F g ^− 1 ) and a capacity of ~ 80 mAh g ^− 1 at a rate of 300C (12-sec charge/discharge time) with over 90% capacitance retention at 70°C during floating tests at -0.83 V vs. Hg/Hg ₂ SO ₄ over a month. By systematically varying electrochemical potential, pH, and temperature, we identify titanium dissolution as the principal degradation pathway in strong acids and establish a direct correlation between titanium loss and capacitance decay. Reducing potential suppresses titanium dissolution, thereby extending electrode lifetime. To rationalize the effects of potential and pH, we constructed computational Pourbaix diagrams for Ti ₃ C ₂ T _x at room temperature. The experimentally observed potential- and pH-dependent stability trends are consistent with the predicted thermodynamic stability domains. Our findings position Ti ₃ C ₂ T _x as a promising negative-electrode material in protic aqueous electrolytes for high-power aqueous energy storage over a wide temperature range and demonstrate how computational Pourbaix analysis, combined with temperature-dependent degradation measurements, can guide the selection of durable electrode–electrolyte combinations for aqueous electrochemical systems.