Self-discharge of redox electrolyte enhanced supercapacitors based on nanosheet-like CoS2

Transition metal sulfides used as electrode materials are becoming increasingly attractive to researchers because of their excellent conductivity and capacitance in supercapacitors with alkaline electrolytes (KOH). However, the mechanism of self-discharge at an open circuit is still unclear. Herein, KOH electrolyte was replaced with redox electrolyte KOH + K3Fe(CN)6 (PFC) to explore the self-discharge mechanism of nanosheet-like CoS2/CC. It was found that the CoS2/CC electrode in the redox electrolyte has high specific capacitance (2325.5 mF cm−2) at the current density of 1 mA cm−2. Afterwards, the self-discharge mechanism and influential factors of redox electrolyte enhanced supercapacitors were investigated using open circuit potential tests and mathematical models. It is worth noting that the device voltage assembled with CoS2/CC electrode decreased from 1.6 V to 0.8 V after the 2680 s in the redox electrolyte, which was faster than the self-discharge time (6435 s) in the KOH electrolyte. The main reason for the rapid self-discharge phenomenon is the limited surface area of the CoS2/CC electrode which has a weak adsorption capacity for redox active groups, allowing charged redox active substances to be transported freely in the electrolyte. At the same time, it objectively shows that the energy stored in the device is constantly dissipating.