Impedance Analysis of Inherently Redox‐Active Ionic‐Liquid‐Based Photoelectrochemical Cells: Charge‐Transfer Mechanism in the Presence of an Additional Redox Couple

An intensive electrochemical impedance study was carried out to understand the charge‐transfer processes in photoelectrochemical (PEC) cells based on ionic liquid (IL) electrolytes. Three different electrolytes were utilized to understand the role of redox species as well as the medium on the charge‐transfer mechanism. The negligible diffusion resistance, despite the presence of two different redox species in the case of Fe(CN)₆^?4/?3 in IL, was explained on the basis of charge transfer between species of two different redox couples. Accordingly, the redox species are not required to travel through the bulk of the electrolyte for the removal of accumulated charges, as short‐range charge transfer between the IL and the Fe(CN)₆^?4/?3 species facilitates the removal of accumulated charges. It is also shown that PEC cells utilizing dual redox couples are highly stable with larger photoelectrochmeical windows, >3 V.