(345d) Micro-Supercapacitors Based-on Mxene Quantum Dots with Ultra-High Rate Capability and Fast Frequency Responsibility

Among the several existing micro-/nano-scale energy storage systems, micro-supercapacitors (MSCs) as promising candidates to power miniaturized portable/wearable electronics have attracted tremendous attention due to their unique merits. However, several key issues such as the relatively low energy density, unsatisfactory rate capability, and narrow operating voltage need to be improved before further applications. Here, we report that the Ti₃C₂T_x MXene-derived quantum dots (QDs) with rich functional groups and abundant active sites are synthesized and employed as electrode material for the MSCs. The resulting MSCs exhibit high-specific capacitance, outstanding rate performance, and fast frequency responsibility in both aqueous electrolytes and ionic liquid electrolytes. This device also displays an excellent high-rate capability demonstrated by the perfect rectangle CV shape even at ultra-high scan rate up to 1000 V·s^-1, a high area specific capacitance of 828.6 μF·cm^-2, and a long-term cycling stability manifested by high capacitance retention after 5000 cycles. The remarkable capacitor performance presented here is attributed to the unique surface and structural features as well as the chemical state, enabling well-exposed Ti₃C₂T_x QDs to the electrolyte and easy transport of the ions and electrons during the charge/discharge process.