基于能带工程的一维CdS核壳结构的构建及光催化分解水制氢研究

Hydrogen generated by photocatalytic water splitting under the sunlight is of critical importance for the development of the clean and sustainable energy in the future. As one of important factors in the system, light absorption materials play an important role for the performance improvement. n-CdS, as a narrow direct band gap semiconductor, has the ability of photoresponse in visible light. Nevertheless, the application in photo-to-electric conversions has been restricted due to the fast recombination between photo-induced electron and hole and the poor photostability. There is an effort to hydrogen production by photoelectrochemical water splitting based on one-dimension (1-D) CdS core/shell array photoanode: (1) 1-D CdS array from aerosol assisted chemical vapor deposition has a lot of advantages, such as crystal face exposed, less boundary and high-efficient transfer of charges. (2) Based on band gap engineering, the charge separation efficient can be improved by deposition the shell with minimal band offset. (3) Merged into the co-catalyst, hole injection efficiency and antiphotocorrosion of the core/shell array can be improved at the same time. We do our best to realize the high-efficient photoelectrochemical water splitting based on 1-D CdS core/shell architectures and expose the mechanism. Not only efficiency, but also stability of photoelectrochemical water splitting could be promoted based on the metal sulfide photoanodes.

利用太阳能在光催化体系下分解水制氢是新能源研究的一个热点问题。作为该体系研究核心之一的吸光材料对其性能的提升起重要作用。n型CdS作为较窄带隙半导体，具有较强的可见光响应能力，然而其较高的光生电子空穴复合率及较差的光稳定性限制了其光电转换应用。本项目拟开展CdS一维阵列的纳米核壳结构光阳极进行光电化学分解水制氢的研究。第一，采用气溶胶辅助化学气相沉积法，制备具有径向定晶面暴露、晶界少、电荷传递效率高等特性的一维CdS阵列；第二，基于能带工程理论，继续沉积能带带偏（Band offset）较小的全包裹壳层材料，抑制光生电子空穴的复合，提升电荷分离能力；第三，在核壳结构的基础上引入助催化剂，增加空穴注入效率、抑制光腐蚀反应，提高复合电极稳定性。最终通过一维CdS核壳光阳极光电化学分解水体系的构建及载流子高效传输机制的研究，实现以金属硫化物为基础的光阳极在光电化学电池效率和寿命上的双重提升。

本项目开展的基于能带工程的一维CdS核壳结构的构建及光催化分解水研究是一种氢能源绿色开发的重要方法。主要研究一维CdS纳米阵列电极的可控制备，并在此基础上包覆能带带偏较小的硫属化合物MnS和In2S3作为壳层材料，构建II型和Z型异质结为基础的核壳结构光阳极，最后在壳层负载析氧助催化剂提升复合催化剂整体的载流子注入效率，最终提升光阳极整体的分解水效率。研究发现通过气溶胶辅助气相沉积法可稳定制备出CdS尺寸在直径50~200 nm、长度1~2 μm之间自由控制的纳米棒，且制备的CdS一维阵列电极具有沿[001]晶向生长的特点；由于表面配位环境的差异，壳层材料的沉积均匀性不太理想，改用温和的离子交换法沉积壳层后，效果较好，制备的MnS材料可与CdS形成紧密的异质结接触，可有效提升光生电子空穴的迁移效率并减少因缺陷导致的界面复合，明显提升了异质结光阳极的分解水效率和稳定性。开发了若干种光解水助催化剂，包括MoS2、CoS2、Co2P、NiPS3、VOOH及FeOOH等，最优的分解水析氧性能可以在190 mV的低过电位下产生10 mA cm-2的电流密度。且开发的分解水助催化剂大多为二维结构，非常适宜在光催化剂表面负载。通过本项目的实施，开发出具有自支撑特性的一维硫化物阵列电极的高效制备方法，通过离子交换法可控构建硫化物异质结可显著提升载流子的分离效率，开发出多种二维分解水助催化剂的制备方法。