Graphitic carbon nitride/zinc oxide composite electrodes for all-solid-state photo-supercapacitor with ion exchange membrane separator

Photo-supercapacitor (PSC) devices, which have the ability to convert solar energy into electricity and store it at the same time, are groundbreaking in the field of renewable energy. However, performing energy conversion and storage on the same system with an efficient and compact design is a very challenging task. In this work, novel graphitic carbon nitride (g-CN)/zinc oxide nanowire (ZnO NW) composites have been synthesized as photoactive electrode material. All-solid-state two-electrode PSC has been assembled by using the lithiated Nafion® membrane as the electrolyte and separator. Compared to the standard filter paper (FP) separator, the Li-form Nafion® membrane provided 5-times higher energy density under UV-illumination, at 1.5 V working potential and at 26.7 mAg current density. Moreover, g-CN/ZnO NW-based PSC having Li-form Nafion® membrane showed excellent cycling stability over 25,000 charge/discharge cycles with exceptional capacitance retention and Coulombic efficiency of 90.2 % and 99.9 %, respectively. In addition, UV illumination resulted in prolonged discharge time. In other words, energy density increased 21.5-fold with UV-illumination and reached 11 Wh kg at 1.5 V working voltage and 20 mAg current density.