The effects of electrolytes on nickel oxide-based electrochemical capacitors

X-ray Photoelectron Spectroscopy was used to characterize the origin of the pseudo-capacitance in nickel oxide-based electrochemical capacitors. The performance of these capacitors varied as a function of the type of electrolyte solution used to fill the capacitor. In aqueous electrolytes, OH-ions represent the predominant counter ions in the double layer and their related surface redox reactions are major contributors to the pseudo-capacitance in this system. A 1 M LiOH electrolyte provides the highest specific capacitance (265 F/g) in these electrochemical capacitor systems. In a non-aqueous electrolyte solution, Li+ ions and their surface insertion reactions contribute to the pseudo-capacitance in this system. This nonaqueous system may be the first electrochemical capacitor that utilizes Li+ insertion reactions as major mechanism for charge storage.