Accelerating Charge Transfer in Supercapacitor Electrodes through Built-In Electric Fields

The commercial development of supercapacitors (SCs) heavily depends on a stable electrochemical performance with a long life span. However, insufficient charge transfer within the SC electrodes is a major challenge. This paper introduces an interface engineering strategy to enhance charge transfer by creating a built-in electric field (BIEF) at the interface of MXene electrode material. Ti₃C₂T MXene decorated with Ti₂N nanocubes was selected as the electrode material, and a stable BIEF was formed at the Ti₂N/Ti₃C₂T interface due to the different surface potentials of Ti₂N and Ti₃C₂T. Our results show that the designed Ti₂N/Ti₃C₂T electrode exhibits a high capacitance of 250.3 F g^-1, an excellent rate capability of 63.6% at 20 A g^-1, and an outstanding cycling stability of 95.8% at 10 A g^-1 after 10,000 cycles in a three-electrode system. The assembled two-electrode device with activated carbon (AC) as the anode, the Ti₂N/Ti₃C₂T//AC, demonstrates an excellent energy storage performance, with an energy density of up to 50.8 Wh kg^-1 and an outstanding cycling stability of 96.77% over 10,000 cycles. The improved energy storage performance and cycling stability are attributed to the accelerated ion transportation and adsorption/desorption on the electrode surface, driven by the electric field force generated by the BIEF. In addition, the in-situ growth of Ti₂N on the Ti₃C₂T surface is conducive to improving the structural stability of the electrode material and promoting the stable existence of the BIEF. This work provides a new pathway for developing ultrastable and high-performance SCs.