text: The photo-reduction of CO on p-type semiconductor photo-electrodes has been achieved in both aqueous and non-aqueous media. Main difference between aqueous and non-aqueous media is the solubility of CO. The solubility of CO in aqueous media at 1 atm. of CO is around ≈ 35 mM; whereas solubility of CO in methanol is around 210 mM and in acetonitrile is around 210 mM.