Ferroelectric polarization controlled surface potential and charge transport across ITO-Nd-doped BiFeO₃ polycrystalline ceramic bulk for photoelectrochemical solar water splitting

The spontaneous polarization in ferroelectrics provides an effective way to engineer interfacial charge distribution at the ferroelectric heterojunctions, thereby depletion width in p-n junction and energy band structures. Here, we integrated p-type multiferroic 7% neodymium-doped bismuth ferrite Bi_0.93Nd_0.07FeO₃ (BFO7Nd) polycrystalline ceramic bulk with n-type transparent conductive indium tin oxide (ITO) to demonstrate the influence of ferroelectric polarization on surface potential and its effect on photoelectrochemical (PEC) water reduction. Kelvin probe force microscopy (KPFM) results reveal the surface potential change during ferroelectric polarization switching, suggesting that the polarization bound charges may have an effect on space charge region between ITO-BFO7Nd, thus dominating surface potential at the electrode/electrolyte interface. This implies that the interface barrier between ITO and BFO7Nd can be easily modulated by polarization bound charges. The electron lifetime of upward-polarization (P-up) ITO-BFO7Nd is estimated 29.30 ms, about 15 times longer than unpoled ITO-BFO7Nd. The photocurrent density of P-up ITO-BFO7Nd is ∼1.2 × 10⁻⁶ A/cm² (at 0 V vs RHE), which is one-order higher compared to that of the unpoled and P-down states under illumination with an intensity of 100 mWcm⁻². This work shows that ferroelectric polarization combined with photogenerated carriers is an effective approach for effective charge transfer in multiferroic ceramic to boost PEC solar water splitting.