Photocatalytic oxidation of water to O2 on AgCl-coated electrodes

Abstract Sustained photocatalytic oxidation of water to O2 on AgCl-coated electrodes is reported. Thin silver chloride layers on different electrode substrates evolve oxygen under near-UV–Vis illumination in aqueous solution at appropriate conditions. The AgCl layers work photocatalytically in the oxidation of water to O2 in the presence of a small excess of Ag+ ions, with a maximum O2 evolution rate at pH 4–5. The light sensitivity in the visible is due to self-sensitization caused by reduced silver species. Many catalytic turnovers with respect to the total amount of AgCl were experimentally realized. Reduced silver species produced during the photocatalytic oxidation of water to O2 on AgCl-coated electrodes can be electrochemically reoxidized by anodic polarization of the electrode. Electrochemical reoxidation can be performed simultaneously with the photochemical water oxidation reaction. The photocurrent is of reversed sign with respect to what has been known as the Becquerel-type photocurrent. Different electrode preparation techniques were investigated, and electrochemical reoxidation turned out to be more efficient on electrochemically prepared AgCl layers than on precipitated AgCl layers. Very stable photoelectrodes have been obtained on SnO2 : F-coated glass plates modified with a very thin gold layer. Such electrodes were employed as the anodic part in a photoelectrochemical cell for light-assisted water splitting.