氧空位在低维氧化铁基光阳极材料中的水分解性能研究

Photoelectrochemical (PEC) water splitting has been widely regarded as one of the most promising routes for fuels converted from solar energy. Hematite offers decisive advantages such as a suitable band gap for sun light absorption and being earth abundant, nontoxic, and chemically stable under photoanodic conditions. However, the water splitting efficiency of hematite was still low, as of some key problems have not been solved, which are mainly focused on the limited light absorption and the corresponding conversion, the serious recombination of electron-hole pairs, and poor oxygen evolution reaction kinetics. According to the previous research results, we propose the combination of introducing oxygen vacancy and construct heterojunction. The aim is to improve charge separation, suppress bulk electro-hole recombination on time scales of millisecond to seconds, and to improve the photocatalytic activity of hematite. On the basics of hematite nanoflakes, oxygen vacancy will be firstly induced on the surface of hematite, and then α-Fe2O3/CuO andα-Fe2O3/Co3O4 heterojunction will be constructed. Through studying the α-Fe2O3/CuO heterojunction, the mechanism that hole transport played a role in photoelectrochemical water splitting will be illustrated. Meanwhile the reasonable explanation about suppression recombination of bulk electron-hole pairs to promote the photoelectrochemical water splitting will be displayed. We will study the photoelectrochemical performance of the hematite-based heterojunction with and without inducing oxygen vacancy on hematite, and explore the role of oxygen vacancy during the interface of hematite-based heterojunction. The ultimate goal is to illustrate the kinetics of the charge carriers in photoelectrochemical water splitting from the view of hole transport and recombination of electron-hole pairs, and to provide new ideas and convictive evidence in photoelectrochemical water splitting.

光电化学水分解是利用太阳能制备燃料的理想途径之一，氧化铁(α-Fe2O3)由于其合适的带隙、无毒以及很好的稳定性可以作为一种非常好的光催化材料。由于对光的吸收转化有限、光生电子-空穴复合严重，以及析氧反应动力学差等，目前α-Fe2O3分解水的效率仍然很低。结合前期工作,申请者提出通过引入氧空位与构建异质结相结合的方式，提高光生电荷分离效率，克服电子-空穴复合严重的问题，提高样品的光催化活性。基于α-Fe2O3纳米片结构，引入氧空位并构建α-Fe2O3/CuO与α-Fe2O3/Co3O4异质结；探索空穴输运和体电子-空穴复合对光电化学水分解性能的影响。通过分析α-Fe2O3基引入氧空位前后所构建异质结的光电化学性能，研究氧空位对α-Fe2O3基异质结光电极中的性能影响，阐明空穴输运与体电子-空穴复合在光催化水分解中的载流子动力学机制，为提高光电化学水分解效率提供新的研究思路与科学依据。

光电化学水分解为有效收集和储存太阳能提供了一种非常有前景的方法与途径。为了更经济、更高效地收集转化太阳能，半导体材料需要具有较高的光吸收、高的转换效率，以及催化活性。在金属氧化物半导体中，氧化铁由于其理想的带隙、性质稳定、无毒、成本低等特点，使其能够成为较好的半导体光电极材料。但是由于α-Fe2O3的低导电率、短的扩散长度、快的电子-空穴复合速率，以及由于光生空穴导致的缓慢的析氧反应，使得α-Fe2O3目前的效率距离理论效率还相差甚远。在本项目中，我们选用了铁箔作为基底，研究了不同的退火温度对氧化铁样品光电化学性能的影响。通过光电流密度和起始电位两个方面分析不同退火条件下α-Fe2O3光电极的光电化学性能，可以发现600℃退火条件的α-Fe2O3样品在1.6V具有最高的光电流密度，其光电流密度达到1.2mA/cm2；但是其起始电位为1.05V，相对较大。我们结合表面形貌与样品结晶度对α-Fe2O3光电极的光电流密度影响进行了探究。为了减少α-Fe2O3光电极的起始电位并进一步提升其光电流密度，我们进一步构建了与CuO的异质结，研究了不同厚度的CuO层对α-Fe2O3光电极在光电化学水分解性能方面的影响。通过结构表征，证实所制备的沉积层为CuO，通过光电化学性能测试，找到α-Fe2O3/CuO异质结的最优性能参数。研究发现，α-Fe2O3/CuO异质结在1.6V的偏压下，光电流可以达到1.5mA/cm2，相比较与α-Fe2O3光电极提升了25%。最后，通过Mott-Schottky测量与电化学阻抗谱数据分析研究发现，α-Fe2O3/CuO异质结更有助于传输累积在氧化铁内的光生空穴，并进一步阐述了CuO在促进α-Fe2O3光电极在光电化学水分解性能中的作用与机制。本项目中α-Fe2O3/CuO异质结的制备与构建对相关半导体光电极提升光生电荷分离以及增加α-Fe2O3光阳极的表面催化活性提供了一种有价值的研究思路与科学依据。