Recently, Fan Fengtao, a researcher at the Dalian Institute of Chemical Physics, 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 charge separation caused by traditional built-in electric fields A diffusion-controlled charge separation process occurs, and the latter contributes more to the charge separation of different crystal planes. Related work was published in "Nature Energy" (Nature Energy).

Understanding the photocatalytic process is a prerequisite for efficient use of solar energy. Among them, understanding the effective separation and migration of photo-excited electrons and holes in semiconductor photocatalysis is the key to improving photocatalytic efficiency. In the early stage, Li Can ’s team used photovoltage measurement technology based on atomic force microscopy to achieve a series of results in the photogenerated charge separation of single-particle nanocrystalline particles: In 2013, on the BiVO4 semiconductor catalyst with regularly exposed crystal planes, chemical oxidation-reduction detection was used. The needle confirmed the photo-generated charge separation effect between different crystal planes of BiVO4 (Nature Comm.); In 2015, the self-developed nano-resolution surface photovoltage spectrum revealed the anisotropic built-in of the space charge layer on different crystal planes of the semiconductor The electric field can show a hole migration anisotropy that is tens of times different, which answers the question of the source of the charge separation driving force on the crystal plane (Angew.Chem.Int.Ed.).

In this work, the research team further used space-resolved surface photovoltage spectroscopy to characterize the photo-generated charge distribution of a single Cu2O particle under asymmetric lighting conditions, and found that symmetric Cu2O particles can produce significant effective charge separation-hole transport to the radiation In the illuminated area, the electron is transmitted to the shaded area. This work distinguishes two charge separation mechanisms, namely the Drifted-Drift Charge Separation Mechanism: It is generated by the built-in electric field of the Cu2O crystal plane, and exhibits a symmetrical distribution in the light and shadow planes. Only the photo-induced minority carriers migrate to the surface, and the surface photovoltage It is 10mV; and Diffused-diffusion charge separation mechanism: the charge separation process caused by the difference in the carrier mobility of electrons and holes, the photovoltage difference between Cu2O and the negative side is 40mV. Quantitative data shows that, in addition to the charge separation process caused by the traditional built-in electric field, the mobility difference of electrons and holes up to two orders of magnitude can produce a diffusion-controlled charge separation process, and the latter contributes more to the charge separation of different crystal planes. Big. Based on the above knowledge, the redox catalysts are deposited on the corresponding crystal planes of single crystal particles, and the photocatalytic performance can be improved by 300%. This research not only reveals a new and effective charge separation driving force in photocatalytic materials, but also provides a new strategy for asymmetric co-catalyst assembly and space-controlled redox reactions.

This work was supported by the "973" project of the Ministry of Science and Technology, the National Natural Science Foundation of China, the pilot project of the Chinese Academy of Sciences, the research and development of scientific instruments and equipment, and the Energy Material Chemistry Collaborative Innovation Center (iChEM) of the Ministry of Education.

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