Boosting the capacitance of MOF-derived carbon-based supercapacitors by redox-active bromide ions

Supercapacitors have attracted tremendous attention due to their merits of excellent cycling stability, remarkable power density and low cost. Nevertheless, the low energy density of supercapacitors has encumbered their further development for practical applications. Development of advanced high-energy supercapacitors is considered to be of crucial importance. In this work, the capacitance of MOF-derived carbon-based supercapacitor is dramatically improved by addition of soluble redox-active LiBr electrolyte additive. The post analysis of this redox-active electrolytes reveal that the Br−/Br2 couple are the main pseudocapacitance contribution in the early cycles stages (<140 cycles), which gradually reaches an equilibrium state and converts into Br–/Br3– redox couples after 160 cycles. The achieved specific capacitance of the assembled supercapacitors is up to 825.6 F g−1 in the added-bromide-ion (ABI) electrolyte. The performance is over seven-fold as high as bromide-free (BF) electrolyte at current density of 1 A g−1.