Solvation effect promoted formation of p–n junction between WO3 and FeOOH: A high performance photoanode for water oxidation

• FeOOH is a cheap water oxidation catalyst that can be photodeposited on WO3.
• FeOOH enhances the charge injection efficiency as well as photocurrent of WO3.
• The formation of hydrogen peroxide on the surface of WO3 can be avoided by FeOOH.
• A p–n junction between WO3 and FeOOH forms under solvation effect.
• FeOOH acts as not only the catalyst but also a hole extractor in the p–n junction.

The accumulation of H2O2 on the surface of WO3 in the process of photoelectrochemical (PEC) water splitting leads to the decrease of photoactivity of WO3. To solve this problem, a thin layer of FeOOH acting as water splitting catalyst was coated on the active sites of WO3 surface. The WO3/FeOOH anode, with a deposition time of 20 min, showed a maximum photocurrent of 1.3 mA/cm2 at 1.23 V vs reversible hydrogen electrode (RHE) under simulated solar illumination (AM 1.5G, 100 mW/cm2). Furthermore, long time photostability of WO3 was achieved by depositing the FeOOH layer ascribed to its water oxidation ability to generate O2 rather than H2O2. Interestingly, we found that a p–n junction between WO3 and FeOOH formed due to the different solvation effects on WO3 and FeOOH. The existence of p–n junction favored the transfer of holes from the WO3 to the FeOOH.

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