A simple and high-effective electrolyte mediated with p-phenylenediamine for supercapacitor

A redox intermedium p-phenylenediamine (PPD) with quick reversible faradaic processes is introduced into KOH electrolyte, referred to as pseudocapacitive effect occurring on the electrode/electrolyte surface. The KOH + PPD electrolyte as potential electrolyte for supercapacitors is investigated by UV-Vis spectroscopy and electrochemical methods. As expected, the supercapacitor with KOH + PPD electrolyte has a much higher electrode specific capacitance (605.225 F g−1) than the one with conventional KOH electrolyte (144.037 F g−1) at the same current density of 1 A g−1. Simultaneously, the supercapacitor with KOH + PPD electrolyte exhibits a much higher energy density (19.862 W h kg−1) than the supercapacitor with conventional KOH electrolyte (4.458 W h kg−1). Furthermore, the supercapacitor with KOH + PPD electrolyte shows superior charge–discharge stability. After 4000 cycles, its capacitive retention ratio is still as high as 94.530%.