Primary photocatalytic water reduction and oxidation at an anatase TiO2 and Pt-TiO2 nanocrystalline electrode revealed by quantitative transient absorption studies

[Display omitted] •Quantitative assessment of electron and hole transfer dynamics at anatase nanocrystalline TiO2 / water interface.•TiO2 conduction band electron, trapped electron and trapped hole absorption spectra were derived by comparing TA spectra.•Water reduction occurs with two single exponential components with difference in time scale of 6∼7 orders of magnitudes.•Water oxidation: Water oxidation reactions occur multi-exponentially in 25 ns to 200 ms.•Pt nanoparticle on the TiO2 surface catalyses both water reduction and oxidation reaction. Quantitative assessments of electron and hole transfer dynamics with water on anatase nanocrystalline TiO2 films were conducted by employing a series of transient absorption spectrometers. For water reduction reactions, both conduction band and trapped electrons decay with two different single exponential components with the difference in time scale of 6∼7 orders of magnitudes. The faster reaction occurs in 8–16 ns, while the slower component shows a lifetime of 0.1∼1.4 s. Pt nanoparticle deposition on the TiO2 surface switches the slower single exponential reaction to a stretched exponential with an accelerated half lifetime of 2–7 ms, indicating that this slower reaction is limited by the electron trapping-detrapping movements inside the TiO2. Water oxidation reactions occur multi-exponentially from 100 ns to 200 ms with a half lifetime of 10 μs. Pt on the TiO2 surface catalyses water oxidation, occurring from 25 ns with a half lifetime of 8 μs.