InP and CdS Photoanodes in Concentrated Aqueous Iodide Electrolytes

Conditions for the efficient photo-oxidation of iodide for both n-CdS and n-InP are demonstrated by theoretical collection properties in rotating ring-disk electrode configurations. A specific I-CdS surface interaction promoting hole transfer kinetics is evidenced by open-circuit potential shifts of illuminated disks with iodide concentration and nearly quantitative disk iodine production at low iodide concentrations. For n-InP, however, high concentrations of CaI₂ and control of hydrogen ion levels are both needed to maintain a thin, charge conducting semiconductor-oxide film and adequate kinetics for solution iodide oxidation. Acidified concentrated iodide is the first electrolyte with an n-InP photoanode to handle solar current densities.