MXene-copper/cobalt hybrids via Lewis acidic molten salts etching for high performance symmetric supercapacitor.

MXenes have attracted great interests as supercapacitors due to their metallic conductivity, high density, and hydrophilic nature. Herein we report Ti3C2-Cu/Co hybrids via molten salt etching in which the existence of metal atoms and their interactions with MXene via surficial O atoms were elucidated by XAFS for the first time. The electrochemical investigation of Ti3C2-Cu electrode demonstrated the pseudocapacitive contribution of Cu and a splendid specific capacitance of 885.0 F g-1 at 0.5 A g-1 in 1.0 M H2SO4. Symmetric supercapacitor Ti3C2-Cu//Ti3C2-Cu was demonstrated with operating voltage of 1.6 V, areal capacitance of 290.5 mF cm-2 at 1 mA cm-2, and stability over 10000 cycles. It delivered an areal energy density of 103.3 μWh cm-2 at power density of 0.8 mW cm-2, based on which a supercapacitor pouch was fabricated. It provides deeper insights into the molten salt mechanism and strategies for designing MXene-based materials for electrochemical energy storage.