多铁性BiMnO3纳米结构的光/光电催化性能及其与压电/铁电极化的关联性研究

Semiconductor photocatalysis technology is one of the most ideal routes for hydrogen production. However, the current developed photocatalysts suffer from low solar energy conversion efficiency. In piezoelectric/ferroelectric materials, the built-in electric field formed by spontaneous polarization can drive the separation of photogenerated electrons and holes effectively, providing a new strategy for developing high-efficiency photocatalytic materials. However, conventional piezoelectric/ferroelectric materials usually have large band gap (> 3 eV), which limits their utilization of the full solar spectrum. To solve these problems, this project intends to develop a novel multiferroic BiMnO3 nanomaterial with narrow bandgap for solar water splitting. The ferroelectric/piezoelectric polarization can be controlled by applying external field (electric field or mechanical force field), which will separate the photogenerated carriers effectively and enhance the photocatalytic water splitting efficiency. We are aiming to optimize the photocatalytic/photoelectrochemical hydrogen production properties and understand the underlying mechanism by revealing the intrinsic relationship between the size/microstructure, ferroelectric/piezoelectric properties of multiferroic BiMnO3 materials. This study may provide useful guidance for designing high efficient photocatalytic water splitting materials and devices based on multiferroic nanostructures.

半导体光催化分解水技术是最为理想的氢能开发手段之一，而目前所研制的光催化剂普遍存在能量转换效率低的瓶颈。压电/铁电材料的自发极化形成的内建电场可以有效驱动光生电子和空穴的分离，为开发高效光催化剂提供了新途径。然而，传统的压电/铁电材料通常具有较大的禁带宽度（大于3eV），限制了其对太阳光谱的充分利用。本项目拟发展新型窄带隙多铁性BiMnO3纳米光解水催化材料，并针对光生载流子分离效率低的问题，提出了利用材料的铁电及压电性质，通过外场作用（电场、机械力场等）激发和调控内部极化电场从而促进光生载流子分离的新思路。通过揭示材料的尺寸/微观结构、压电/铁电性质和光/光电催化性能之间的内在联系，最终优化多铁性BiMnO3纳米材料光解水制氢性能，并完善压电/铁电极化对材料能带结构及光生载流子输运的调控机制。项目的研究有望为设计高氢能-光能转换效率的多铁性材料及器件提供一定的实验依据和理论指导。

利用压电/铁电材料的极化电场可以有效调控表面能带弯曲及载流子输运，为高效机械能/光能-化学能转换提供了崭新的途径，有望在诸多催化领域获得新应用。本项目以两种典型的压电材料KNbO3和Bi0.5Na0.5TiO3为研究对象，揭示了关键参数(微观结构、压电系数、电导率)对压电催化性能的影响机制。对不同微观形貌的KNbO3纳米材料对比研究发现，KNbO3纳米片的压电催化性能明显优于纳米立方体。压电原子力显微测试(PFM)和有限元模拟(FEM)理论计算均表明，在外加应力下，KNbO3纳米片产生了更大的压电电势。上述结果表明，具有高纵横比的纳米结构具有更优异的压电催化性能，为设计高效纳米压电催化材料提供了依据。并且可通过铁电极化有效调控光电流，该研究为高效压电催化材料和智能光电器件的设计提供了指导方案。此外，本项目通过系统分析多种压电材料的压电系数、电导率和压电催化效率之间的关系，首次提出电导率对压电催化性能起到决定性作用。为获得最优性能，需要协同优化压此发现，申请人将同时具有良好的压电性能及相对较高的电导率的Bi0.5Na0.5TiO3首次引入压电催化领域。与已经报道的压电材料体系相比，Bi0.5Na0.5TiO3纳米材料具有更高的催化性能，该研究为开发高性能压电催化材料提供了新的视角和筛选标准。