Unveiling the Effects of Nanostructures and Core Materials on Charge-Transport Dynamics in Heterojunction Electrodes for Photoelectrochemical Water Splitting.

Understanding the photogenerated charge-transport dynamics of metal oxide electrodes is the key to providing a strategy for practical improvement in the photoelectrochemical reaction activity. Here, we analyze the electron transport of a 3D bicontinuous SnO2/BiVO4 nanostructured photoelectrode by intensity-modulated photocurrent spectroscopy. We compare this electrode with 3D WO3/BiVO4 and planar-type bilayer SnO2/BiVO4 electrodes. In the results, we observe an order of magnitude faster electron transport in the 3D electrodes relative to the bilayer electrode. Moreover, we observe trap-limited transport on widely applied WO3/BiVO4 electrodes but confirm rapid trap-free transport on 3D SnO2/BiVO4. We also characterize the effect of electron transport on the water-splitting reaction. The electron-transport rate is directly related to the charge-separation efficiency in the water-splitting reaction. The fast transport time of the 3D SnO2/BiVO4 leads to the achievement of a significantly higher charge separation efficiency of 94%.