Ferroelectric-Photocatalyst Nanocomposite Thin Films for Enhanced Photoelectrocatalytic Activity

Low-cost, oxide-based photo-electrocatalysts (PEC), such as Fe₂O₃, BiVO₄, CuWO₄, are gaining increased attention to achieve unassisted water splitting to produce solar fuels. Although they possess ideal bandgaps in the range of 2-2.5 eV, they suffer from a high level of surface recombination and low carrier mobility¹. Ferroelectric polarization has emerged as a new strategy in photocatalysis to induce opposite band bending at material surfaces facilitating increased charge separation and promoting selective redox reactions². However, most ferroelectric have wide bandgaps, and therefore do not absorb visible light, and are insulating therefore cannot transport photogenerated charges. Therefore, herein, we combine ferroelectric BaTiO₃ with the photocatalyst Fe₂O₃ in parallel at the nanoscale to combine the benefits of ferroelectrics and photocatalysts in a nanocomposite film.<br/> <br/>To produce this structure, porous BaTiO₃ (pBTO) thin films were synthesized by the soft template-assisted sol-gel method. Using different concentrations of organic template, the porosity of pBTO was controlled to obtain suitable thin films for photocatalyst integration. The overall porosity and surface area of the pBTO thin films is determined by SEM analysis and ellipsometry.<br/> <br/>The ferroelectric phase of pBTO is confirmed by XRD analysis and Raman spectroscopy. The switching of spontaneous polarization of pBTO by an electric field is verified by Piezoresponse Force Microscopy (PFM). The alignment of polar dipoles to the ferroelectric surface (P_up or P_down) is evaluated by testing the PEC performance of pBTO after electrochemical (EC) poling at ±8V, which show that the photoanode performance is improved for P_down.<br/> <br/>Lastly, the pBTO/Fe₂O₃ thin film shows an enhancement of the photocurrent density compared to either the bare Fe₂O₃ (by ∼2 times) and pBTO thin films (by ∼20 times), which could be correlated to the upward band bending induced by the ferroelectric polarization of pBTO. The PEC response in pBTO/Fe₂O₃ is accordingly regulated by EC poling without altering the Fe₂O₃ layer chemically (as confirmed by XPS), leading to further enhancement of the photocurrent. This research work shows a facile and low-cost approach for the development of novel ferroelectric/photocatalyst photoanodes with switchable control of their PEC performance, which possess a great potential for photoelectrochemical applications.<br/> <br/><b>References </b><br/>S. Kment, Chem. Soc. Rev., 2017, <b>46</b>, 3716.<br/>F. Chen, <i>Angew. Chem. Int. Ed.,</i> 2019, <b>58</b>, 10061-10073.