Electrochemistry in mesoporous electrodes: influence of nanoporosity on the chemical potential of the electrolyte in dye sensitized solar cells

The illumination of a dye sensitized solar cell (DSSC) shifts the chemical potential of the electrolyte positively with respect to its dark value. This shift is a result of the charge separation process in which electrons are injected into the TiO₂ electrode and positive charges are transferred to the electrolyte. In this study, we attempted to measure the electron density in TiO₂ under operating conditions by monitoring the hole concentration (chemical potential) in the electrolyte solution. However, the results obtained showed that the chemical potential of the electrolyte in DSSCs is not solely determined by the redox concentrations. The charging of the mesoporous medium alters the electrochemical parameters inside the electrode volume. These changes refer to the ionic strength, the ionic activity, or the standard potential. Consequently, we describe a phenomenon to control the electrochemical potential of an electrolyte solution by altering the nanometric pore size of the TiO₂ matrix. While significant for both the analysis and the design of DSSCs, this new phenomenon opens a path for the manipulation of electrochemical processes utilizing mesoporous electrodes.