g-C3N4/碳纳米管双层复合薄膜的制备及光电化学性能研究

In recent years, graphitic carbon nitride (g-C3N4) has attracted great attention due to its potential applications as multipurpose metal-free photocatalysts. A new task in this research area is to construct high-performance photoelectrochemical cells based on g-C3N4 thin films. There still remain significant challenges to enhance the structural uniformity as well as to improve the extremely poor conductivity of g-C3N4 thin films. In this proposal we plan to fabricate highly uniform g-C3N4 thin films by using a vapor-condensation deposition technique, to suppress the drawback of the boundary effect. On the other hand, we plan to fabricate g-C3N4/carbon nanotube (CNT) double-layer composite thin films, in which the conductivity could be improved and the photoinduced charge carriers could be rapidly separated and transported. We propose to carry out the following studies: 1) to develop a double-zone deposition system with more controllable parameters, fabricate high-quality g-C3N4 thin films and reveal their formation and growth mechanism; 2) to fabricate g-C3N4/CNT double-layer composite thin films, demonstrate the interfacial interaction and the transport progress of the photo-induced charger carriers; 3) to construct prototypical photoelectrochemical devices by using the composite thin films as photoanodes, investigate the effect of CNT thin film on the device performance, which could possess remarkably enhanced photocurrent densities up to 300 μA/cm2 under the standard measurement conditions.

近年来石墨相氮化碳（g-C3N4）的光催化特性备受关注，构建基于g-C3N4薄膜的高性能光电化学器件是该领域所面临的新挑战。如何提高g-C3N4薄膜的结构均匀性，改善它的导电特性是目前所要解决的关键性问题。本项目拟通过改进气相聚合沉积技术来制备结构高度均匀的g-C3N4薄膜，消除颗粒边界效应的不利影响；通过构建g-C3N4/碳纳米管双层复合薄膜来改善其导电性，促进光生电荷的快速分离与传导。具体研究内容：1）g-C3N4薄膜制备：采用双温区设计来增加气相沉积的可控性，制备结构均匀的高质量薄膜并阐明其形成和生长机理；2）双层复合薄膜：在g-C3N4薄膜上沉积碳纳米管薄膜，揭示其间的界面结合以及载流子传导机制；3）光电化学性能：以双层复合薄膜为光电极构建原理性器件，研究表层的碳纳米管薄膜对器件性能的影响规律，在标准测试条件下使其光电流密度提高到300 μA/cm2以上。

石墨相氮化碳（g-C3N4）具有理想的能带结构和优异的化学稳定性，在光催化和光电催化领域的应用备受关注。构建基于g-C3N4薄膜的高性能光电化学器件是该领域所面临的新挑战。如何提高g-C3N4薄膜的结构均匀性，改善它的导电特性是目前所要解决的关键性问题。本项目发展了两步法气相聚合沉积新技术，制备出结构均匀致密、表面平滑、透光度良好的高质量g-C3N4薄膜，消除了颗粒边界效应的不利影响；通过构建g-C3N4/碳纳米管双层复合薄膜改善了表面导电特性，促进了光生电荷在薄膜/电解液界面之间的快速分离与传导，实现了光电化学性能的显著提升。取得的研究结果包括：（1）g-C3N4薄膜的可控制备及表征：发展了两步法气相聚合沉积g-C3N4薄膜的新方法，改善了薄膜的结构均匀性和表面粗糙度，揭示了薄膜结构对其光电化学特性及稳定性的影响规律；（2）g-C3N4薄膜的生长机理及厚度控制：阐明了g-C3N4热解聚合的反应动力学过程，分析了g-C3N4薄膜的成膜和生长机理，揭示了薄膜厚度对光电化学性能的影响规律；（3）双层复合薄膜的制备及光电化学性能研究：构建了g-C3N4/碳纳米管双层复合薄膜，分析了薄膜的光生载流子分离与传导机制，对双层复合薄膜的光电化学性能进行了优化；（4）g-C3N4及其中间产物的电子结构及红外光谱表征：计算了g-C3N4及其中间产物的电子结构，模拟了它们的红外光谱，为分析g-C3N4与碳纳米管之间的相互作用及相关体系的光谱表征提供了理论支撑。在标准测试条件下，双层复合薄膜的光电流密度稳定在270 μA/cm2左右，比g-C3N4薄膜提高了4倍。本项目的研究结果表明通过构建g-C3N4/碳纳米管双层复合薄膜能够显著提升其光电化学性能，在光电化学催化和分解水析氢领域具有重要的应用前景。