Interface Engineering and its Effect on WO3-Based Photoanode and Tandem Cell.

During photoelectrochemical (PEC) water splitting, the reactions occur on the surface of the photoelectrode. Therefore, the properties of the interfaces between the various components of the electrode (semiconductor/semiconductor, semiconductor/catalyst, or photoelectrode/electrolyte) affect the PEC performance of the composite material. Notably, surface trap states may hinder charge transfer and transport properties, and also cause Fermi pinning, affecting the quasi-Fermi level and onset potential under illumination, which may in turn influence the PEC performance of the corresponding tandem cells. In this study, plate-like WO3 array films prepared by an aqueous chemical growth method were employed to highlight the effect of interfacial properties on the performance of a WO3-based photoanode. The Mott-Schottky and linear sweep voltammetry experiments prove the existence of surface trap states and Fermi pinning for pristine WO3, which are alleviated after an "etching" treatment and disappeared after surface passivation by a Ga2O3 layer. Both etching and passivation increase the oxygen evolution activity and the Faradaic efficiency for the oxygen evolution reaction (OER). After loading a permeable catalyst (FeOOH), the photocurrent is further increased, and there is a synergistic effect between loading of the electrocatalyst with etching or passivation. The onset potentials of the samples follow the trends: etch-WO3/FeOOH < WO3/FeOOH ≤ WO3/Ga2O3/FeOOH < etch-WO3 < WO3 < WO3/Ga2O3, indicating that the interfacial properties have a significant effect on the PEC performance. Meanwhile, the modified WO3-based electrode was combined with a dye-sensitized solar cell to fabricate tandem cell, which showed 2.42-fold photocurrent density compared with the pristine WO3-based tandem cell.