半导体量子点敏化光电极与其表面分子组装的界面电荷转移动力学研究

This proposed project seeks ways to further improve the photocatalytic efficiency of water splitting and to construct a photoelectrochemical tandem cell for total water splitting. Currently, molecular catalyst based photo-electrodes encounter two major kinetic challenges. One is fast interfacial charge recombination rates in microseconds to hundreds of microseconds time scale. The other is that multiple charge accumulation rates to the catalytic center is approximately in the same time window. Therefore, we propose to study photoinduced charge transfer kinetics at the interfaces of the photo-electrodes. We design wide band gap nanocrystalline metal oxide semiconductor modified by II-VI semiconductor quantum dots (QD) as the light harvester. The surface of the semiconductor QD will be functionalized by charge transfer molecules and catalytic molecules. Solution processing will be the main method to assemble and modify the QD sensitized photo-electrodes. We will focus on the investigation of photoinduced surface charge migration and interfacial charge recombination kinetics by using UV-Vis transient absorption spectroscopy and transient anisotropy. In addition, we will evaluate the light conversion efficiency to oxygen or hydrogen from water by using the photoanodes and the photocathodes with various assemblies. The link among photo-electrode assembly, interfacial kinetics, and light conversion efficiency will be explored. Finally, a photoelectrochemical tandem cell consisting the selected high efficiency photoanode and photocathode will be attempted to construct for total water splitting without external applied biases.

为寻求进一步提升分子光催化水分解产能效率，构筑全水分解光催化串联器件，并且针对目前分子光催化电极的光生电荷复合速率快（微秒至几百微秒量级）而多电荷聚集速率慢（几乎与电荷复合同等时间量级）的两大动力学问题，本项目拟设计使用II-VI族半导体量子点修饰的纳米晶型宽禁带金属氧化物半导体为光吸收主体，对量子点表面进行电荷传递分子和催化分子功能化，从而研究光生电子空穴对在此类光电极界面的电荷转移动力学。该项目拟采用溶液法对半导体量子点敏化电极进行组装和修饰，重点运用紫外可见瞬态吸收光谱和瞬态各向异性光谱对光激发后量子点界面电荷传递和电极界面电荷复合进行系统性的动力学研究，同时对不同光阳极和光阴极进行产氧和产氢性能测试，探索光电极组装、界面动力学与光能转化三者的内在联系，最后串联高效率光阳极和光阴极，尝试构筑无需外加电压辅助的光催化全水分解器件。

为寻求进一步提升分子光催化水分解产能效率，构筑全水分解光催化串联器件，并且针对目前分子光催化电极的光生电荷复合速率快（微秒至几百微秒量级）而多电荷聚集速率慢（几乎与电荷复合同等时间量级）的两大动力学问题，本项目设计并合成了半导体量子点修饰的纳米晶型宽禁带金属氧化物半导体作为光吸收主体，通过在量子点表面进行电荷传递分子和催化分子的功能化，研究了光生电子和空穴在半导体和量子点界面的电荷转移动力学。重要结果包括: 1）通过对硫化镉量子点表面的空穴传递分子修饰，光生空穴的寿命得到数量级的提升，光电催化水氧化反应效率随电荷转移动力学的优化而显著提升，以钒酸铋为半导体的光阳极产氧效率逼近理论值，研究成果为光电催化电池器件应用于太阳能的高效转化与利用提供了新的电极组装思路。2）染料分子修饰的金纳米簇界面电荷分离态达近秒级别，实现高效光催化还原硝基芳香类底物。3）利用半导体界面修饰分子的空穴传递，实现了无偏压辅助，纯太阳能驱动串联电池全水分解产氢0.11%的效率，为所有报道的染料分子敏化光电合成电池中的最高值，为光电合成电池走向太阳能高效转化的实际应用迈出了坚实的一步。