Photoelectrochemical Cells for the Oxidation of Water and Bromide Ions by Visible Light

Anodic oxidation of water to molecular oxygen and of bromide ions to Br2photosensitized by tris‐bipyridylruthenium(II), Ru(bpy)32+, has been investigated in photoelectrochemical cells. An irreversible photoredox reaction between Ru(bpy)32+and electron acceptors (S2O2–, Tl3+, Co(NH3)5Cl2+) generates Ru(bpy)33+which is reduced at the cathode (Pt or Carbon) with concomittant oxidation of H2O or Br−with RuO2, Pt (or Carbon) anodes respectively. Cell performances have been examined in terms of photocurrents, potentials under illumination, stability, turn‐overs, and the data explained in terms ofi‐ecurves of the redox couples involved in Evans‐type diagrams. Under optimal conditions, photocurrents upto 10 mA (with a 250 W lamp) have been drawn and 2 · 10−4mdes Br2generated in one hour photolysis. Possible extensions, scope and limitations are discussed.