Ferroelectric polarization is a potential way to enhance electron-hole carrier separation in photocatalysts for the water-splitting reaction, a pathway to hydrogen fuel from sunlight and water. Here, we show that the application of electric fields (85 kV/cm) to particle films of barium titanate (BaTiO3, Eg = 3.0 eV) and strontium titanate (SrTiO3, Eg = 3.2 eV) leads to increased water oxidation photocurrents (BaTiO3 = 10.4 µA cm-2, SrTiO3 = 70 µA cm-2) under UV illumination (24 mW cm-2). For BaTiO3, the enhancement occurs after electrical polarization at room temperature, which suggests it is due to a ferroelectric polarization of the material. For SrTiO3, which is non-ferroelectric, the observed photocurrent enhancement is most dominant after annealing the material at 1050 oC in forming gas atmosphere (10% H2 in argon). This treatment is known to produce oxygen vacancies, which appear to be involved in the polarization. Both materials were further characterized with Kelvin probe measurements and surface photovoltage spectroscopy (SPS). These confirm that the orientation of the electric field controls the contact potential difference (CPD) and the direction of carrier separation. Additionally, X-ray photoelectron spectroscopy was used to determine the local chemical composition and workfunction of the materials. The impact of these findings on the development of improved water splitting photocatalysts will be discussed.

Investigation of electrical polarization for enhancement of photoelectrochemical water splitting in barium titanate and strontium titanate particle films

ACS Spring 2022

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