Bias-free photoelectrochemical water-splitting using epitaxial (Pb,La)TiO₃ thin films

Photoelectrochemical (PEC) water splitting is known to be an effective method for H₂ production. For practical usages, however, it is desirable that the PEC cells are operated under a bias-free condition which does not require any consumption of additional energy. Since a few years ago, investigations on ferroelectric materials have been conducted because they inherently possess internal electric fields. (Pb,La)TiO₃ (PLT) is a renowned material because of its good ferroelectric characteristics. We deposited c-axis oriented epitaxial-PLT thin films on platinized MgO001 (PLT/Pt/MgO). From above, photocathodic responses were verified, and specifically, quite large photopotential (V_ph) of more than 2.42 V were observed. The V_ph is attributed to a highly stabilized polarization in the PLT, and the value was sufficiently larger than the potential required for water splitting (1.23 V + overpotential, η). It enabled the hydrogen evolution reaction (HER) under bias-free conditions.

Fig. Schematics for a photocathode including an epitaxial PLT thin film as a photoactive material at an equilibrium state (left) and under a sufficient illumination (right).