Boosting hematite photoelectrochemical water splitting by decoration of TiO₂ at the grain boundaries

Hematite has been one of the most promising candidates for solar water splitting while addressing its poor bulk charge transfer has been always challenging towards its practical application. We show here an efficient strategy of boosting the charge transfer of hematite photoanode by decorating the grain boundaries in Fe₂O₃ film with TiO₂ based on a simple chemical bath deposition. Such strategy resulted in dramatically improved photocurrent density up to 2.90 mA cm⁻² at 1.23 V vs. RHE. The IPCE and APCE of the Fe₂O₃/TiO₂ photoanode demonstrated a significant increase to 68% and 95% at 360 nm, respectively. Further investigations reveal that the enhanced PEC performance can be attributed to the improved charge separation efficiency, increased charge carrier density, as well as the enlarged contact area between electrolyte and photoanode. Moreover, modification of the Fe₂O₃/TiO₂ nanoporous film with FeOOH catalyst could achieve a photocurrent of 3.15 mA cm⁻² at 1.23 V vs. RHE. We thus believe that our study of decorating grain boundaries by an inorganic layer provides an alternative to address the charge transfer of hematite based photoelectrodes.