Diphenylcarbazide-based carbon materials: Novel redox additives for simply and largely improving the electrochemical performance

• Diphenylcarbazide acts as both carbon source and redox additive.
• Electron and proton transfers occur in the redox additive–carbon material system.
• Introducing redox additive has highly improved the supercapacitor performance.
• Redox additive into KOH electrolyte can be realized at ambient condition.

In this work, we demonstrate two kinds of novel redox additives, diphenylcarbazide (abbr. DC) and phenylazoformic acid 2-phenylhydrazide (abbr. PP), with quick and reversible redox reaction incorporated into carbon-based supercapacitors. It is revealed that the 4-electron and 4-proton transfer occurring in the redox additive–carbon material system within the electrode can result in additional capacitance. When introducing 24 mg DC or PP substance into 24 mg carbon system, largely improved specific capacitances of 544.3 or 427.6 F g− 1 are achieved, which are almost 4.31 and 3.39 times, respectively, than that of the pristine carbon (126.1 F g− 1) at the current density of 2 A g− 1. Besides, their corresponding capacitance retentions can reach up to 78.9% and 75.6%, respectively, after 5000 charge–discharge cycles, and both of them are somewhat smaller than that of the pristine carbon (96.8%) due to the incremental electronic resistances. The present commercially available, low-cost and highly effective redox additives of DC and PP are quite promising and expected to be implemented for high performance supercapacitors.