Semiconductor-sensitised thermal cells (STC) are a new type of thermal energy conversion system that makes effective use of waste heat even at low-temperature. This system generates electricity via the redox reactions of electrolyte ions caused by thermally-excited carriers in the semiconductor electrode. However, there has been no direct proof of the redox reactions. In this manuscript, these reactions were directly observed via the change in colour of copper electrolyte ions, depending on their valence. This observation indicated that the oxidation reaction occurred at the semiconductor electrode and the reduction reaction occurred at the counter electrode, as we expected. These results will lead to the clarification of the principles and improvement of the STC performance.

Single-phase powders of LaMnO 3 and LaCoO 3 , lanthanum-based perovskites, were synthesized using the citric acid combustion method. The surface concentration of La in the obtained powder was higher in LaCoO 3 than in LaMnO 3 . These samples decomposed 2-naphthol in water in the dark. The decomposition reaction is attributed to the Marsvan Krevelen (MvK) mechanism because of the temperature dependence, activation energy, valence change during the reaction, and the amount of ion elution into water. A disproportionation reaction was confirmed for Mn in LaMnO 3 . Both samples exhibited antibacterial and antiviral activity against Escherichia coli, Staphylococcus aureus, bacteriophage Q¢, and bacteriophage ¯6. The antibacterial activity was higher than the antiviral activity. LaCoO 3 tended to have higher antibacterial and antiviral activity than LaMnO 3 had. Results show that these materials had less ion leakage than that reported earlier for La 2 Mo 2 O 9 .