Fluorine-doped tin oxide/ hematite/ Ni(OH)2/ Prussian white photoelectrode for use in a visible-light-assisted pseudocapacitor

Abstract

Herein, a fluorine-doped tin oxide/hematite/nickel hydroxide/Prussian white photoelectrode is fabricated for use in a visible-light-assisted pseudocapacitor. A visible-light-assisted pseudocapacitor is a two-electrode device that uses both electrical and solar energy sources to charge and store energy. The photoelectrode consists of a thin layer of Prussian white deposited on a nickel hydroxide modified hematite film. The hematite is used as a photoactive material, nickel hydroxide and Prussian white are employed as the pseudo-capacitive electroactive materials. Fluorine-doped tin oxide/hematite/nickel hydroxide/Prussian white has a much higher charge-discharge time and areal capacitance under illumination. A galvanostatic charge-discharge curve shows an areal capacitance of 2.16 mF cm−2 under illumination, that is 940-fold higher than that in the dark. This behavior is attributed to the presence of photogenerated charges that increase the conductivity and facilitate charge transfer reactions. The electrochemical impedance spectroscopy shows that the charge transfer resistance under illumination is 633 Ω which is more than three times lower than 2220 Ω under dark. Therefore, under dark pseudocapacitive charge storage reactions do not occur significantly, because of the high resistance of semiconductor. While under illumination, photogenerated charges reduce charge transfer resistance. Thus, the pseudocapacitive reaction is progressed and the charge is stored.