Charge-transfer mechanism in Pt/KTa(Zr)O₃ photocatalysts modified with porphyrinoids for water splitting

The mechanism of photocatalytic splitting of H₂O into H ₂ and O₂ on Pt/KTa(Zr)O₃ modified with various porphyrinoids was investigated. The photocatalytic activity of KTaO₃ catalysts is improved by dye modification. Cyanocobalamin (vitamin B ₁₂) is the most effective for improving watersplitting activity, and the formation rates of H₂ and O₂ achieved values of 575 and 280 μmolg_cat ^-1h^-1, respectively. X-ray photoelectron spectroscopy spectra of KTa(Zr)O₃ photocatalysts showed that Pt loaded onto dye-modi-fied KTaO₃ was slightly oxidized and had low catalytic activity for the H₂ oxidation reaction. Photoluminescence (PL) spectra of KTaO₃ catalysts suggested that excitation energy was transferred between KTaO₃, tetraphenylporphyrinatochromium(III) (Cr-TPP), and the Pt cocatalyst. The wavelength dependence of the activity of dye-modified KTa(Zr)O₃ photocatalysts indicated that excitation of both KTa(Zr)O₃ and the dye was essential for achieving increased photocatalytic activity. This result suggests that twostep excitation occurred in the dyemodified KTa(Zr)O ₃ photocatalysts. Because the lifetime of the charge-separated state increased, this study reveals that modification with porphyrinoids is effective for increasing watersplitting activity.