Long-time charge separation in porphyrin/KTa(Zr)O3 as water splitting photocatalyst

Artificial photosynthesis is one of the chemists' dreams and the separation of charges with long lives is fundamental for achieving artificial photosynthesis. In actual photosynthesis, Z-scheme excitation separates electronic charge with high efficiency using solar light. Here we report that photo-excitation in Cr-tetraphenylporphyrin chroride (Cr-TPPCl)/Zr doped KTaO3 (KTa(Zr)O-3) is analogous to the Z-scheme in photosynthesis, and that we achieve complete charge separation at room temperature. Photovoltaic decay and transient fluorescence spectra measurements showed that the photo-excited charge in KTa(Zr)O-3 transferred to the HOMO of Cr-TPPCl within a few hundred pico-seconds on charge transfer. In contrast, the reduced state of the Cr-TPPCl species that was formed by the electronic injection from KTa(Zr)O-3 was observed for more than 0.5 s at room temperature in the transient decay of the absorption spectra change after the initial excitation of KTa(Zr)O-3. The formed reduced state of Cr-TPPCl was highly stable and was detected by static ESR measurements.