The photo-electrochemistry of the Rhodamine B-hydroquinone system at optically transparent bubbling gas electrodes

Use of the technique called ‘bubbling gas electrode’ yields very reproducible polarograms on solid electrodes. It is applied here to study the photoelectrochemistry of the Rhodamine B-hydroquinone system on optically transparent n-type SnO₂ and gold electrodes, in order to understand the operation of a photovoltaic cell based on due-supersensitizer couples.Rhodamine alone gives no photo-currents on gold, and weak ones on SnO₂; added hydroquinone gives rise to very intense photo-currents on both electrodes. Increasing supersensitizer concentrations lead to a plateau, allowing an estimate of the lifetime of an electro-active transient.Two mechanisms for supersensitization are envisioned: hydroquinone can donate an electron to the photo-electrogenerated oxidized rhodamine, reducing thus the cathodic tunnel-current; or the diphenol might transfer an electron to the photo-excited dye, producing thus a new oxidizable species. Taken alone, the second mechanism is unable to explain all findings.Action spectra, recorded for a large number of experimental conditions suggest a major contribution from adsorbed dye molecules; in the presence of hydroquinone, some contributions from the solution may be operative.