Recently, Fan Fengjun, a researcher at the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences, and Li Can, a member of the Chinese Academy of Sciences, used a self-developed surface photovoltage imaging instrument to clarify the difference in mobility between electrons and holes compared to the traditional built-in electric field. A diffusion-controlled charge separation process is produced, and the latter contributes more to the charge separation of different crystal faces. Related work is published in Nature Energy.
The understanding of the photocatalytic process is a prerequisite for the efficient use of solar energy. Among them, the understanding of the effective separation and migration of photoexcited electrons and holes in semiconductor photocatalysis is the key to improving the photocatalytic efficiency. The Lican team used the light based on atomic force microscopy in the early stage. The voltage measurement technique has achieved a series of results in the photo-generated charge separation of single-particle nano-grains: In 2013, on the BiVO4 semiconductor catalyst with regularly exposed crystal faces, chemical redox probes were used to confirm the different crystal planes of BiVO4. The photo-generated charge separation effect (Nature Comm.); In 2015, using the self-developed nano-resolved surface photovoltage spectrum, it revealed that the semiconductor built-in electric field with anisotropy in the space charge layer of different crystal planes can show tens of times difference. The hole migration anisotropy answers the source of the driving force of the crystal face charge separation (Angew.Chem.Int.Ed.).
In this work, the research team further utilized the spatially resolved surface photovoltage spectrum to characterize the photo-generated charge distribution of individual Cu2O particles under asymmetric illumination conditions. It was found that symmetric Cu2O particles can produce significant charge-effective separation—hole transport to the spoke The area is electronically transmitted to the shadow area. This work distinguishes between two charge separation mechanisms, the Drifted-drift charge separation mechanism: generated by the built-in electric field of the crystal plane of Cu2O, which exhibits a symmetric distribution in the illumination and shadow planes, which is only beneficial to The photogenerated minority has migrated to the surface, and its surface photovoltage is 10mV; and the Diffused-diffusion charge separation mechanism: the charge separation process caused by the difference in carrier mobility between electrons and holes, and the photovoltage difference between Cu2O and the matte surface is 40mV. The data show that in addition to the traditional built-in electric field, the charge separation process, electrons and holes up to two orders of magnitude difference in mobility, can produce a diffusion-controlled charge separation process, and the latter contributes more to the charge separation of different crystal faces. Based on the above knowledge, the redox catalysts are respectively deposited on the corresponding crystal faces of the single crystal particles, and the photocatalytic properties can be
The work was funded by the Ministry of Science and Technology '973' project, the National Natural Science Foundation of China, the Chinese Academy of Sciences Pilot Project, the Research Instrument and Equipment Development Project, and the Energy Materials Chemistry Collaborative Innovation Center (iChEM) of the Ministry of Education.
