Department of Chemistry and Biochemistry, University of Berne
Freiestrasse 3, CH-3012 Bern, Switzerland
Silver chloride layers on different substrates evolve O2 from water with high quantum yield when irradiated with near-UV and visible light under appropriate conditions. The reaction showing self-sensitization is favoured in the presence of a small excess of Ag+ ions that act as electron acceptors, according to eqn. (1).
| [nAg+,mAgCl] | + | r/2 H2O | ---> | [(n-r)Ag+ mAgCl rAg0] | + | rH+ | + | r/4 O2 | (1) |
We have now found a route to reoxidize the reduced silver electrochemically according to eqn. (2), which means that photocatalytic water oxidation with thin AgCl layers on different electrode substrates can be achieved [1].
| [(n-r)Ag+ mAgCl rAg0] | ---> | [nAg+ mAgCl] | + | re- | (2) |
In a photochemical experiment the result of which is shown in the Figure the O2 evolution of an electrochemically prepared, thin AgCl layer on an SnO2 electrode was measured during alternating illumination (350-750 nm, ~50 mW/cm2) and dark periods. Simultaneously the electrode was polarized at 0.0 V vs. Hg / Hg2SO4 (+0.64 V vs. NHE) and the current was measured. The amount of O2 that was produced until the experiment was stopped after 12 h corresponded to more than 5 turnovers of the AgCl layer, and more turnovers can be achieved by longer illumination. The reduced silver was almost quantitatively reoxidized in this experiment, as calculated from the current signal.
| [1] | M. Lanz and G. Calzaferri, J. Photochem. Photobiol. A: Chem. 109 (1997) 87. |
