The Effect of Chloride Anions on Charge Transfer in Dye-Sensitized Photoanodes for Water Splitting

The photoelectrochemical behavior of dye-sensitized photoelectrochemical cells based on a TiO₂ layer sensitized with ruthenium components, including an absorber, ruthenium(II)bis(2,2'-bipyridine)([2,2'-bipyridine]-4,4'-diylbis(phosphonic acid)) dibromide (RuP), and a catalyst, ruthenium(II) tris(4-methylpyridine)(4-(4-(2,6-bis((l1-oxidanyl)carbonyl)pyridin-4-yl)phenyl) pyridine-2,6-dicarboxylic acid) (RuOEC), was investigated in the following water-based electrolyte configurations: KCl (pH ≈ 5), HCl (pH ≈ 3), ethylphoshonic acid (pH ≈ 3) with a different KCl concentration, and a standard phosphate buffer (pH ≈ 7). The rate of charge transfer on the photoanode's surface was found to increase in line with the increase in the concentration of chloride anions (Cl^-) in the low pH electrolyte. This effect is discussed in the context of pH influence, ionic strength, and specific interaction, studied by cyclic voltammetry (CV) in dark conditions and upon illumination of the photoanodes. The correlations between photocurrent decay traces and CV studies were also observed.