基于钙钛矿型氮氧化物BaTaO2N的高效光电催化水分解光阳极的开发

Perovskite-type oxynitride BaTaO2N is a direct band gap semiconductor with wide visible light absorption and proper band positions, which is a very suitable photoanode light absorber for photoelectrocatalytic water splitting. However, currently the performance of BaTaO2N photoanode is still very low. This is because the synthesis methods developed so far are only suitable for the preparation of power sample. Photoelectrode prepared from BaTaO2N power has several limitations including low charge collection efficiency and high interfacial recombination. Developing fabrication method of high quality thin film structure that is suitable for integrating into photoelectrode is expected to greatly improve the photoelectrocatalytic water splitting performance of BaTaO2N photoanode. Therefore, we propose to use a dual-electron beam co-evaporation method to deposit BaTaOx precursor film, which is then nitrided in ammonia at high temperature to obtain BaTaO2N film. Ba and Ta ions in the electron beam co-evaporated precursor film distribute uniformly and the film is amorphous. This will greatly lower the thermodynamic barrier for ion diffusion and rearrangement, which is beneficial for improving the crystallinity of the BaTaO2N film. Furthermore, the opto-electronic properties of the BaTaO2N film will be thoroughly characterized, which can provide guidance for the optimization of film quality. Based on the obtained high-quality BaTaO2N thin film, hybrid photoanode consisted of p-n junction, protection layer, and oxygen-evolution catalyst layer will be constructed to realize high efficiency and high stability photoelectrocatalytic water splitting.

钙钛矿型氮氧化物BaTaO2N是一种具有宽可见光吸收、合适能带位置的直接带隙半导体，适合作为光阳极吸光材料用于光电催化水分解。但是，目前BaTaO2N光阳极的性能还很低。这是由于目前的制备方法仅适用于粉末样品，用粉末来构筑光电极存在低电荷采集效率、高界面复合等限制。开发适合光电极组装的高质量薄膜结构的制备方法，有望显著提升BaTaO2N光阳极的光电催化水分解性能。因此，我们拟采用双电子束共蒸的方法沉积BaTaOx前驱体薄膜，再使用氮化的方法制备BaTaO2N薄膜。电子束共蒸的方法可以使前驱体薄膜为非晶态且Ba、Ta离子均匀分散，这将大大降低氮化过程中离子扩散和重排的热力学壁垒，有利于提高BaTaO2N薄膜的晶体质量。进一步地，将对BaTaO2N薄膜光电性质系统地表征，为优化薄膜质量提供指导。在此基础上，通过p-n结、保护层、产氧催化剂层的构筑实现高效率、高稳定性的光电催化水分解复合光阳极。

本项目围绕如何提升薄膜光阳极材料吸光能力、促进光生电荷分离、增强表面催化转化等关键科学问题，在BaTaO2N及Ta3N5等氮（氧）化物薄膜的可控制备、氮（氧）化物薄膜光阳极的同质结/异质结构筑、高效析氧助催化剂修饰等方面开展了系统地研究工作。开发了使用双电子束共蒸和氮化方法可控制备BaTaO2N薄膜及Mg、La掺杂Ta3N5薄膜的工艺，研究了通过梯度Mg掺杂在Ta3N5薄膜内部构筑梯度能带结构的方法，使用Mg掺杂GaN和In掺杂GaN分别修饰Ta3N5薄膜的上下界面构筑“p-i-n”型异质结光阳极，并通过异质掺杂的策略构筑梯度Mg:Ta3N5/La:Ta3N5同质结以解耦薄膜光吸收和载流子传输性能，以及开发高效自修复析氧助催化剂用于增强表面催化转化等。通过本项目的实施，显著提升了钽基氮（氧）化物光阳极光电催化分解水的水氧化效率，实现了半电池太阳能-氢能转化效率（HC-STH）最高为4.07%的世界纪录值。相关成果已经有23项公开发表在学术刊物上（均标注了本项目基金号，其中18项为第一标注），包括Nature Catalysis、Nature Communications（3篇）、Angewandte Chemie、ACS Catalysis（3篇）、ACS Energy Letters等第一标注论文，并申请了相关专利3项。