Scanning Photoelectrochemical Microscopic Study in Photoinduced Electron Transfer of Supramolecular Sensitizers-TiO₂ Thin Films Systems

Abstract

Crafting charge transfer channels at titanium dioxide (TiO₂) based photoanodes remain a pressing bottleneck in solar-to-chemical conversion technology. Despite the tremendous attempts, TiO₂ as the promising photoanode material still suffers from sluggish charge transport kinetics. Herein, we propose an assembly strategy that involves the axial coordination grafting metalloporphyrin-based photosensitizer molecules (MP) onto the surface-modified TiO₂ nanorods (NRs) photoanode, forming the composite MP/TiO₂ NRs photoelectrode. As expected, the resulted unique MP_B/TiO₂ NRs photoelectrode displays significantly improved photocurrent density as compared to TiO₂ NRs alone and MP_A/TiO₂ NRs photoelectrode. Scanning photoelectrochemical microscopy (SPECM) and intensity modulated photocurrent spectroscopy (IMPS) were employed to systematically evaluate the continuous photoinduced electron transfer (PET) dynamics for MP/TiO₂ NRs photoelectrode. According to the data fitting, it is found that the photoelectron transfer rate (k_eff) constant for the MP_B/TiO₂ NRs is about 2.6 times higher than that for the pure TiO₂ NRs under light irradiation. The high kinetic constant for the MP_B/TiO₂ NRs was ascribed to that the conjugated molecules MP_B of D-A structure can effectively accelerate intramolecular electrons transfer as well as promote electrons taking part in the reduction reaction of I₃^- to I^- in the novel charge transfer channel. The results demonstrated in this study are expected to shed some light on investigating the mechanism in the charge transfer process of artificial photosynthesis and constructing efficient photoelectrodes.

Keywords

photosensitizer / TiO₂ nanorods / Scanning photoelectrochemical microscopy / photoexcited electron transfer

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