Charge Recombination with Fractional Reaction Orders in Water-Splitting Dye-Sensitized Photoelectrochemical Cells

• DOI: 10.1021/jacs.8b04878
• Publication Date: 2018-08-27T04:36:15Z
• Authors: Pengtao Xu; Christopher L. Gray; Langqiu Xiao; Thomas E. Mallouk
• Keywords: Charge carrier; Photoelectrochemistry; Photoelectrochemical cell

In water-splitting dye-sensitized photoelectrochemical cells (WS-DSPECs), charge recombination competes with catalytic water oxidation to determine the overall efficiency of system. The kinetics these processes have been difficult understand because transient absorbance (TA) experiments typically show nearly complete on submillisecond time scale; in contrast, electrochemical measurements such as open circuit photovoltage decay suggest a scale that is 2–3 orders magnitude longer. Here we explore nanocrystalline TiO2 and TiO2/Ta2O5 core–shell photoanodes aqueous electrolytes using TA spectroscopy, intensity-modulated spectroscopy (IMVS), impedance (PEIS). fast rates measured by result from strong laser excitation leads high electron occupancy TiO2, whereas IMVS modulates concentration charge-separated states near solar irradiance levels. methods IMVS, PEIS, are discharging injected electrons evidenced close agreement between first-order probed RC constants derived PEIS data. However, at variable probe light intensity reveal reaction for oxidized sensitizer molecules far unity. This kinetic analysis relevant understanding steady-state full WS-DSPECs which molecular nanoparticle catalysts used oxidize water.