基于二维半导体材料的网络结构复合光电极的制备及其光电催化分解水性能研究

Photocatalytic water splitting is the key reaction in photo-to-chemical energy conversion, and how to improve its conversion efficiency is one of the most important issue in this field. The low light absorption efficiency, the high recombination probability of photoinduced carriers, and the slow charge transfer rate cross the semiconductor/solution interfaces are three main factors that restrain the improvement of photo-to-chemical energy conversion. In this project, we are aimed at constructing oriented network-structured composite photoelectrodes via controlled growth of two-dimensional (2D) semiconductor materials (SM) and decoration of the network with electrochemical co-catalysts. The high light-capture efficiency and large specific area of oriented network structure, the short transport distance of photoinduced carriers in 2D SM from where they are generated to the semiconductor/solution interface, and the fast charge transfer rate due to the presence of co-catalyst, may significantly improve the photo-to-chemical conversion efficiency. On the basis of above-mentioned ideas, we will develop and optimize methods for the preparation of network-structured composite photoelectrodes, which are composed of 2D SM. We will illustrate the dependence of light absorption efficiency on the structure of single crystalline or heterojunction network composites. We will develop effective method both to extend the light absorption range and to improve the light absorption efficiency of the network composites. We will also explore the separation and transport of photoinduced charge carriers in the network structure, identify the key factors controlling the charge separation and transport process. Moreover, we will investigate the transfer mechanism of photo-induced charge carriers across the “2D SM/co-catalyst/solution” interfaces, and clarify why the modification of electrochemical co-catalyst on the surface of network struture can improve the energy conversion efficiency during photoelectrochemical water splitting. We hope the results of this project can shed light on how to develop photoelectrocatalytic cells with novel structure, high energy conversion efficiency and low cost.

光解水是光化学能转化的关键问题。制约其能量转化效率提高的主要因素是光吸收效率低、光生载流子在传输过程中复合几率高、半导体/溶液界面电荷传递速率慢。本项目通过控制二维半导体材料在电极表面的生长，构筑有取向的交叉网络结构，并负载助催化剂，形成网络结构复合光电极。利用取向网络结构光捕获效率高、比表面积大，二维材料内光生载流子到达反应界面的传输距离短，助催化剂加速电荷界面传递速率等优点，提高光化学能转化效率。基于以上思路，本项目拟建立和完善上述网络结构复合光电极的制备方法；揭示单晶和异质结二维半导体材料构成的网络结构在光吸收过程中的构效关系，发展拓宽光吸收范围、提高光吸收效率的方法；阐明光生电子-空穴对在单晶及异质结半导体网络中的分离和传输规律及其影响因素；探索网络结构中的光生载流子在“半导体/助催化剂/水溶液”界面间的传递过程及机理。为新型、高效、低成本光电催化体系的设计和研制提供新的思路。

光电催化分解水是光能-化学能转化领域的重要课题, 光吸收效率低、光生载流子复合几率高、半导体/溶液界面电荷传递速率慢是制约其能量转化效率的主要因素。本项目主要研究内容包括：研究低维半导体材料的交叉网络结构、层状结构、阵列结构的制备方法，探索上述结构对光吸收效率、光生电荷分离效率、界面电荷传递效率的影响，提高光电催化分解水效率。.主要研究结果如下：（1）建立和完善了二维半导体纳米片交叉网络结构（WO3、CuWO4、CuWO4/BiVO4）、二维层状异质结（Cu2O/CuO、CuO/CuBi2O4）、树枝状网络结构（CuBi2O4、CuBi2O4/TiO2）、纳米线阵列结构（Cu2O、Cu2O/SnO2）复合光电极的制备方法。（2）揭示了上述不同结构与光吸收的构效关系，发展出基于离子掺杂、构筑异质结（Cu2O/CuO、CuO/CuBi2O4、CuWO4/BiVO4）等拓宽光吸收范围的方法、显著提高了上述复杂结构光电极的光吸收效率。（3）明确了光生电子-空穴对在半导体网络结构中的分离和传输过程及其影响因素，建立了提高网络结构和层状结构半导体材料导电性的方法，阐明了缺氧环境热处理、离子掺杂影响材料导电性的机理，揭示了导电性影响光电催化分解水性能的原因。（4）研发了多种析氢、析氧电催化剂；并将其应用于各种结构半导体光电极，阐明了光生载流子在“半导体/电化学助催化剂/水溶液”界面间的传递过程及机理，揭示了电化学助催化剂提高光电催化分解水效率的原因。（5）建立了在复杂结构光电极表面构筑纳米尺度宽禁带半导体保护层（钝化层）的方法，揭示了钝化层提高光电极稳定性的机理。本项目所获得的光电催化分解水性能是同种半导体材料中最高或较高的，在相关领域的国际主流科技期刊发表了19篇研究论文，获得了国际同行的广泛关注与引用，其中1篇论文成为SCI高被引论文。本项目的研究结果为新型、高效、低成本光电催化体系的设计和研制提供新的思路。