The effect of electrolyte additives on dye regeneration kinetics of indoline dye-sensitized ZnO photoanodes investigated via scanning electrochemical microscopy.

Approach curves in the feedback mode of scanning electrochemical microscopy (SECM) are used for the analysis of the dye-regeneration kinetics on DN216-sensitized porous zinc oxide electrodes in electrolytes containing a cobalt-bipyridine complex as a redox mediator as well as lithium cations and 4-tert-butylpyridine as additives. The mass transport limitation of the mediator through the porous electrode is addressed by tuning the thickness of photoanodes. Continuum simulations of the mediator transport, the electron transport in the semiconductor, photooxidation, dye regeneration and loss processes help to reveal the combined effects of a variety of phenomena in porous photoanodes on the externally measured quantities for different photoanode thicknesses, electrolytes and illumination conditions.