Abstract
Solar-driven photocatalytic reactions offer a promising route to clean and sustainable energy, and the spatial separation of photogenerated charges on the photocatalyst surface is the key to determining photocatalytic efficiency. However, probing the charge-separation properties of photocatalysts is a formidable challenge because of the spatially heterogeneous microstructures, complicated charge-separation mechanisms and lack of sensitivity for detecting the low density of separated photogenerated charges. Recently, we developed surface photovoltage microscopy (SPVM) with high spatial and energy resolution that enables the direct mapping of surface-charge distributions and quantitative assessment of the charge-separation properties of photocatalysts at the nanoscale, potentially providing unprecedented insights into photocatalytic charge-separation processes. Here, this protocol presents detailed procedures that enable researchers to construct the SPVM instruments by integrating Kelvin probe force microscopy with an illumination system and the modulated surface photovoltage (SPV) approach. It then describes in detail how to perform SPVM measurements on actual photocatalyst particles, including sample preparation, tuning of the microscope, adjustment of the illuminated light path, acquisition of SPVM images and measurements of spatially resolved modulated SPV signals. Moreover, the protocol also includes sophisticated data analysis that can guide non-experts in understanding the microscopic charge-separation mechanisms. The measurements are ordinarily performed on photocatalysts with a conducting substrate in gases or vacuum and can be completed in 15 h.
Key points
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Probing the charge-separation properties of photocatalysts is a formidable challenge because of the spatially heterogeneous microstructures, complicated charge-separation mechanisms and low density of separated photogenerated charges.
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Surface photovoltage microscopy as described in this protocol has sufficiently high spatial and energy resolution to enable direct mapping of surface-charge distributions and quantitative assessment of the charge-separation properties of individual photocatalyst particles.
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Data availability
All data generated or analyzed during this study are available at https://figshare.com/ (https://doi.org/10.6084/m9.figshare.24466933.v1) or from the corresponding author upon reasonable request.
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Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (22372159, 22102173, 22088102 and 22325205), the Young Elite Scientist Sponsorship Program by CAST (YESS20220177), the National Program on Key Basic Research Project (2021YFA1500600 and 2021YFA1502300), CAS Projects for Young Scientists in Basic Research (YSBR-004) and Interdisciplinary Innovation Team (JCTD-2018-10) and the Dalian Institute of Chemical Physics Innovation Foundation (DICPSZ201801).
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C.L. conceived and proposed the project. R.C. and F.F. carried out the project. R.C. conceived the protocol, performed the experiments, analyzed the data and wrote and edited the manuscript. C.N. assisted in organizing procedures, J.Z. assisted in experimental setup and F.F. and C.L. revised the manuscript.
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Nature Protocols thanks Hongqi Sun and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Key references using this protocol
Chen, R. et al. Chem. Soc. Rev. 47, 8238–8262 (2018): https://doi.org/10.1039/C8CS00320C
Chen, R. et al. Nat. Energy 3, 655–663 (2018): https://doi.org/10.1038/s41560-018-0194-0
Chen, R. et al. Nature 610, 296–301 (2022): https://doi.org/10.1038/s41586-022-05183-1
Chen, R. et al. Nano Lett. 19, 426–432 (2019): https://doi.org/10.1021/acs.nanolett.8b04245
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Chen, R., Ni, C., Zhu, J. et al. Surface photovoltage microscopy for mapping charge separation on photocatalyst particles. Nat Protoc (2024). https://doi.org/10.1038/s41596-024-00992-2
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DOI: https://doi.org/10.1038/s41596-024-00992-2
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