Bias-free Photo-electrochemical Water Splitting Driven by Large Photopotential of Epitaxial (Pb,La)TiO₃ Ferroelectric Thin Films

Recently, photo-electrochemical (PEC) water splitting has been spotlighted as a promising technique for H₂ production using solar energy. To enhance the solar-to-hydrogen (STH) conversion efficiency by preventing the recombination of photogenerated charges inside photoactive materials, investigations have been initiated on ferroelectrics that inherently possess internal electric fields. (Pb,La)­TiO₃ (PLT) is a renowned material because of its excellent ferroelectric characteristics. We deposited c-axis-oriented epitaxial-PLT thin films on platinized MgO001. Using PLT/Pt/MgO, PEC performances were evaluated and photocathodic responses were verified. In particular, a giant photopotential (V_ph) of more than 2.42 V was obtained, attributing to a highly stabilized polarization in PLT. Such a V_ph was sufficiently larger than the potential required for water splitting (1.23 V + overpotential, η), and it enabled the hydrogen evolution reaction (HER) under bias-free conditions.