Photodeposition of Ag₂S Quantum Dots and Application to Photoelectrochemical Cells for Hydrogen Production under Simulated Sunlight

UV light irradiation of TiO(2) (λ > 320 nm) in a mixed solution of AgNO(3) and S(8) has led to the formation of Ag(2)S quantum dots (QDs) on TiO(2), while Ag nanoparticles (NPs) are photodeposited without S(8). Photoelectrochemical measurements indicated that the Ag(2)S photodeposition proceeds via the preferential reduction of Ag(+) ions to Ag(0), followed by the chemical reaction with S(8). The application of this in situ photodeposition technique to mesoporous (mp) TiO(2) nanocrystalline films coated on fluorine-doped SnO(2) (FTO) electrodes enables formation of Ag(2)S QDs (Ag(2)S/mp-TiO(2)/FTO). Ag(2)S/mp-TiO(2)/FTO has the interband transition absorption in the whole visible region, while in the spectrum of Ag/mp-TiO(2)/FTO, a localized surface plasmon resonance absorption of Ag NPs is present centered at 490 nm. Ag(2)S QD-sensitized photoelectrochemical cells using the Ag(2)S/mp-TiO(2)/FTO and Ag/mp-TiO(2)/FTO photoanodes were fabricated. Under illumination of one sun, the Ag(2)S photoanode cell yielded H(2) at a rate of 0.8 mL·h(-1) with a total conversion efficiency of 0.29%, whereas the Ag/mp-TiO(2)/FTO photoanode is inactive.