Photosensitizing ruthenium(ii)–dye multilayers: photoinduced charge separation and back electron transfer suppression

Abstract

Photocatalytic H₂ evolution activity of three types of Ru(II)-photosensitizer(PS)-multilayered Pt-cocatalyst loaded TiO₂ nanoparticles, RuCP²@Pt–TiO₂, RuCP²–Zr–RuP⁶@Pt–TiO₂, and RuCP²–Zr–RuP⁴–Zr–RuP⁶@Pt–TiO₂ were investigated in the presence of the redox-reversible iodide electron donor aqueous solution. The apparent quantum yield (AQY) significantly improved by about 40 times by increasing the number of Ru(II)–PS layers and decreasing the loading amount of Pt cocatalyst on the surface of TiO₂ nanoparticles. The zeta potential measurement suggests that the Zr⁴⁺ cations between the PS-layers acted as the iodide capturing sites to promote the electron donation. Photocurrent–voltage characteristics of the Ru(II)–PS-multilayered photoelectrodes RuCP²@TiO₂–ITO, RuCP²–Zr–RuP⁶@TiO₂–ITO, and RuCP²–Zr–RuP⁴–Zr–RuP⁶@TiO₂–ITO in aqueous I⁻/I₃⁻ electrolyte solution revealed that the thicker Ru(II)–PS-layer with the Zr⁴⁺ cations contributes not only to suppressing the back electron transfer from Pt–TiO₂ surface to the oxidized iodine species but also to enhancing the photoinduced electron injection.