Aldol condensation products during photocatalytic oxidation of ethanol in a photoelectrochemical cell

Electric current was produced in a photoelectrochemical cell during photocatalytic oxidation of ethanol, which was used as a representative organic compound present in wastewater from biomass processing industries. Thus, the cell behaved as a PhotoFuelCell that consumed waste material to produce electricity. The cell consisted of two compartments separated by a silica frit. The anode electrode was a Fluorine-doped Tin Oxide transparent electrode bearing nanocrystalline titania Degussa P25, applied as a paste and calcined at 550 °C. The cathode electrode was a carbon-cloth bearing Pt/Carbon-Black catalyst. The electrolyte was 1.0 M NaOH. When 20%v. ethanol was added in the anode compartment, the cell gave 0.75 mA/cm2 short-circuit current density (calculated over 12 cm2 electrode area) and 1.1 V open-circuit voltage. The anode compartment of the cell was operated under three different conditions: (1) under continuous air flow, i.e. oxygen-rich conditions; (2) under Ar flow, i.e. anaerobic conditions; and (3) exposed to ambient air but without any gas flow through the cell, i.e. oxygen-deficient, mass transfer-limited conditions. In the latter two cases, the oxidation of ethanol and its photo-oxidation products was incomplete and resulted in aldol condensation reactions that produced various aldehydes, some of them of high molecular weight and insoluble. It was concluded that in order to avoid such reactions, which impede mineralization process, measures should be taken for continuous oxygen supply and for optimal combination of the quantity of the photocatalyst and the concentration of the photodegradable substance. Thus only 1%v. ethanol can give 75% of the maximum current obtained in the presence of large ethanol concentration.

Figure optionsDownload as PowerPoint slideResearch highlights▶ Electric current is produced by photocatalytic oxidation of ethanol in a PhotoFuelCell. ▶ Under oxygen-deficient conditions in the anode compartment, the performance of the cell can be impeded by aldol condensation reactions.