Photochemical Experiments with Ag/AgCl Electrodes

Abstract

Quantitative experiments on the photo-induced chlorine evolution in aqueous dispersions of silver zeolites containing chloride ions have shown that the system is capable of spectral sensitization, an effect we call self-sensitization. There was an argument that the photoproduction of chlorine with visible light is only possible immediately after exposing the system to UV-photons. We now deliver experimental results which unequivocally prove that this is wrong. The large driving force of the back reaction Ag + ½ Cl₂ → AgCl of E° = 1.14 V must be considered to approve the photoproduction of chlorine with visible light. Despite of the high electrochemical potential, the recombination reaction is kinetically blocked. Based on these observations we have succeeded to construct a photogalvanic {Ag/AgCl||Cl^⊖/Cl₂} cell with a theoretical open-circuit potential of 1.14 V. Experimental open-circuit potentials of 1.05 V are regularly obtained and the power voltage curves exhibit a maximum around 730 mV. Encouraging experiments carried out with sunlight show the interesting performance of the system and the advantage of the short-time storage capacity.