All chemicals were of analytical grade and used without further purification. Throughout all experiments, deionized water (pH 7.3, 18.3 MΩ cm -1 ) in the laboratory was sourced on Milli-Q ultrapure (Type 1) water purification system (Biopak® Polisher, Merck, USA). Before use, the fluorine-doped tin oxide (FTO, surface resistivity ∼7 Ω sq -1 , Sigma Aldrich) coated glass substrates were ultrasonically cleaned with isopropanol, acetone, and a mixture of alkaline concentrate (Hellmanex III) and deionized water for 10 min each.