Nano-TiO 2-flavin adenine dinucleotide film redox processes in contact to humidified gas | salt electrolyte

Redox processes in nano-TiO 2-flavin adenine dinucleotide (TiO 2-FAD) layer-by-layer assembled films on ITO substrate electrodes are investigated and compared in contact to aqueous electrolyte media (for dilute and saturated electrolyte) and in contact to solid humidified salt electrolyte (for extreme salt levels and different types of salts). Under these unusual conditions an aqueous microphase present at the gas | salt | electrode interface allows voltammograms to be obtained and redox processes to be analysed. It is demonstrated that the 2-electron 2-proton reduction of FAD can be used as reporter redox system to determine local pH at the electrode | gas | salt interface as pH 15, 12, 7 for contacts to K 3PO 4, K 2HPO 4, and KH 2PO 4, respectively. Exposure to gases such as carbon dioxide is shown to lead to unexpected changes in surface pH. In the future, bio-electrochemical microphase processes under halophilic conditions could be useful for air-quality and rapid gas sensing devices.