Photoelectrochemistry is a promising approach for converting solar energy to storable chemical energy in chemical fuels. The efficiency of these photoeletrodes depends critically on efficient transfer of charge carrier across the electrode liquid interface to drive chemical transformation. Although transient absorption spectroscopy is a powerful tool for probing interfacial dynamics in high surface area electrodes, it is often not applicable on planar electrodes because the observed signal is often dominated by carrier dynamics in the bulk. In this paper, we report a study of carrier dynamics in planar photoelectrodes using transient reflection spectroscopy. Compared to transient absorption, this method is more sensitive to surface carrier density that can be more directly correlated to catalysis. We showed that transient reflectance change can be used to follow charge carrier dynamics and their amplitude can be directly correlated to IPCE for water reduction on TiO2 protected p-GaP single crystals. Our finding suggests that IPCE is determined by the efficiency of initial ultrafast (&lt; hundreds of ps) charge separation across the GaP/TiO2 interface despite the much slower water reduction reaction. It is also observed that transient band flattening by high charge carrier density is a key loss mechanism in these devices. In ongoing studies we are applying transient reflectance spectroscopy to photoanodes for water oxidation and developing new methods that can directly probe the extend of transient band flattening.

In situ transient reflectance probe of water reduction/oxidation kinetics at semiconductor photoelectrode/liquid interface

2019 Fall National Meeting

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