Recently, the research group of Professor Chen Qianjin at the College of Chemistry and Chemical Engineering has made significant progress in the field of scanning electrochemical imaging. This work was recently published in the Journal of the American Chemical Society (JACS) under the title "Deciphering Site-Specific Kinetics on Shaped Pd Nanocrystals via Single-Particle Electrocatalysis."
The particle size, morphology, and surface structure of nanocrystal catalysts significantly influence their electrocatalytic activity and selectivity. However, even structurally well-defined nanocrystals simultaneously contain multiple local structural sites on their surfaces, including facets, edges, vertices, and defects. Conventional macroscopic electrochemical measurements yield only averaged responses from a large number of catalyst particles, making it difficult to distinguish the intrinsic catalytic contributions of different surface sites. Therefore, establishing a clear structure-activity relationship at the single-nanoparticle scale and deciphering the site-specific kinetics of different sites remain key scientific questions in this field.
This work employed shape-controlled palladium nanocubes as model catalysts and developed an in situ SECCM–TEM measurement method combining scanning electrochemical cell microscopy with transmission electron microscopy, achieving precise measurement of the hydrogen evolution reaction activity of individual Pd nanocrystals and quantitative identification of different surface sites on the same particle. The research team dispersed and loaded Pd nanocubes of different sizes onto carbon-film copper grid substrates, obtained the local electrochemical response of individual particles for the hydrogen evolution reaction using a microdroplet electrochemical cell, and confirmed the structural information of the corresponding specific particles by correlocal transmission electron microscopy. This approach overcame the spatial resolution limitations of conventional SECCM–SEM correlative measurements and enabled single-particle electrocatalytic analysis of Pd nanocrystals as small as 8 nm.
Single-particle electrochemical results showed that the hydrogen evolution reaction (HER) activity of Pd nanocubes is closely related to particle size. As the particle size decreased, the catalytic activity normalized to the unit surface area increased, indicating that the low-coordinated edge sites, which account for a higher proportion in smaller particles, may be the dominant active centers for the HER. By further combining geometric models with single-particle statistical results, the research team classified the surface sites of Pd nanocubes into facet sites and edge sites, and quantitatively resolved their intrinsic catalytic contributions. The results showed that the turnover frequency of Pd edge atoms for the HER was approximately 4.3 times that of facet atoms, directly demonstrating the dominant role of low-coordinated edge sites in the HER on Pd nanocrystals.
To further verify this conclusion, the research team designed and synthesized edge-selectively Au-covered Pd–Au nanocubes and fully Au-covered Pd–Au nanocubes. Single-particle measurements showed that after the edges were selectively covered with Au, the HER current of the particles decreased significantly, and when the particle surfaces were completely covered with Au, the HER activity almost disappeared. Density functional theory calculations indicated that the reaction energy barrier at Pd edge sites is lower than that at facet sites, consistent with the experimentally obtained site-specific activity trend, thereby elucidating the key role of edge sites in the HER on Pd nanocrystals from both experimental and theoretical perspectives.
This work not only quantitatively revealed the intrinsic electrocatalytic differences between facet and edge sites in Pd nanocubes at the single-particle scale, but also established a SECCM–TEM correlative imaging method that can be further extended, providing a viable methodological platform for deciphering the effects of active sites, structural heterogeneity, and elemental distribution on catalytic performance in complex nanocatalysts. This study is of great significance for deepening the understanding of structure–activity relationships in nanoscale electrocatalysis and for the rational design of highly efficient electrocatalysts.
This work was supported by the National Natural Science Foundation of China and other projects. Wu Zengyan, a 2022 master's student at the College of Chemistry and Chemical Engineering, Zhang Weitong, a 2024 doctoral student, and Fan Wenxuan, a master's student at Anhui University of Technology, are co-first authors of the paper. Professor Chen Qianjin from Donghua University and Professor Liu Mingkai from Anhui University of Technology are co-corresponding authors. Donghua University is the first corresponding institution. This research received collaborative support from Professor Zeng Jie of Anhui University of Technology/University of Science and Technology of China.
Original link to this article: https://pubs.acs.org/doi/10.1021/jacs.6c03289
