Unravelling the pH-depended mechanism of ferroelectric polarization on different dynamic pathways of photoelectrochemical water oxidation

Ferroelectric polarization is considered to be an effective strategy capable of improving the oxygen evolution reaction (OER) of photoelectrocatalysis. The frontier challenge is to clarify how the polarization field control the OER dynamic pathway from molecular details. Here, using the electrochemical fingerprints tests together with theoretical calculations, we systematically investigate the free energy change of oxo and hydroxyl intermediates on TiO2-BaTiO3 core-shell nanowires (BTO@TiO₂) under polarization in different pH environments. We demonstrate that in the adsorbate evolution mechanism (AEM) dominated in acid environment, both positive and negative polarization result in a reduction of the oxo free energy, thereby inhibiting the reaction kinetics. In the oxide path mechanism (OPM) occurred mainly in alkaline condition, ferroelectric polarization exhibits a repulsive adsorbate-adsorbate interactions for OH- coverage and free energy shift of hydroxyl groups. We elucidate that a weakly alkaline electrolyte is the optimal application environment for ferroelectric polarization, the positive polarization promotes the OH- coverage and facilitate reaction pathway transfer from AEM to OPM, thus BTO@TiO2 exhibited a record polarization enhancement of 0.52 mA/cm2 at 1.23 VRHE in pH=11. This work provides a more accurate insights into the pH-depended effect of ferroelectric polarization on OER dynamic pathway than conventional models that are based solely on the band bending regulation.