Abstract
Carbon dioxide electroreduction facilitates the sustainable synthesis of fuels and chemicals1. Although Cu enables CO2-to-multicarbon product (C2+) conversion, the nature of the active sites under operating conditions remains elusive2. Importantly, identifying active sites of high-performance Cu nanocatalysts necessitates nanoscale, time-resolved operando techniques3,4,5. Here, we present a comprehensive investigation of the structural dynamics during the life cycle of Cu nanocatalysts. A 7 nm Cu nanoparticle ensemble evolves into metallic Cu nanograins during electrolysis before complete oxidation to single-crystal Cu2O nanocubes following post-electrolysis air exposure. Operando analytical and four-dimensional electrochemical liquid-cell scanning transmission electron microscopy shows the presence of metallic Cu nanograins under CO2 reduction conditions. Correlated high-energy-resolution time-resolved X-ray spectroscopy suggests that metallic Cu, rich in nanograin boundaries, supports undercoordinated active sites for C–C coupling. Quantitative structure–activity correlation shows that a higher fraction of metallic Cu nanograins leads to higher C2+ selectivity. A 7 nm Cu nanoparticle ensemble, with a unity fraction of active Cu nanograins, exhibits sixfold higher C2+ selectivity than the 18 nm counterpart with one-third of active Cu nanograins. The correlation of multimodal operando techniques serves as a powerful platform to advance our fundamental understanding of the complex structural evolution of nanocatalysts under electrochemical conditions.
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All relevant data are available from the corresponding author on request.
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Acknowledgements
This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, & Biosciences Division of the US Department of Energy under contract nos. DE-AC02-05CH11231 and FWP CH030201 (Catalysis Research Program). Work at Cornell University (in particular, operando EC-STEM) was supported by the Center for Alkaline-Based Energy Solutions, an Energy Frontier Research Center programme supported by the US Department of Energy, under grant no. DE-SC0019445. This work made use of TEM facilities at the CCMR, which are supported through the National Science Foundation Materials Research Science and Engineering Center (NSF MRSEC) programme (no. DMR-1719875). This work also used TEM facilities at the Molecular Foundry, supported by the Office of Science, Office of Basic Energy Sciences of the US Department of Energy under contract no. DE-AC02-05CH11231. This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. This work is based on research conducted at the Center for High-Energy X-ray Sciences (CHEXS), which is supported by the National Science Foundation under award DMR-1829070. We thank J. Grazul and M. Thomas at Cornell for TEM technical support, and R. Dhall and K. Bustillo at NCEM. We thank H. Celik and UC Berkeley’s NMR facility at the College of Chemistry (CoC-NMR) for spectroscopic assistance. Instruments in the CoC-NMR are supported in part by NIH S10OD024998. We thank Y. Li for the initial discussion on in situ TEM. We thank R. Page and S. McFall for X-ray cell fabrication at the machine shop of Cornell LASSP. Y.Y. acknowledges support from the Miller Research Fellowship. S.Y. acknowledges support from the Samsung Scholarship. J.J. and C.C. acknowledge support from the Suzhou Industrial Park Scholarship.
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Y.Y., S.L. and S.Y. designed the project under the guidance of P.Y. and H.D.A. Y.Y. performed atomic-scale STEM–EELS and operando EC-STEM measurements. Y.Y. performed operando 4D-STEM, with the help of Y.-T.S. and under the guidance of D.A.M. S.L. and I.R. synthesized Cu nanocatalysts and performed CO2RR performance measurements, with the help of M.V.F.G. and J.F. S.Y. performed X-ray diffraction analysis and H-cell measurements. I.R. performed GDE measurements. Y.Y. performed operando HERFD-XAS studies, with help from S.L., S.Y. and X.H. C.J.P. provided generous support for the operando HERFD set-up. Y.Y. performed operando RSoXS studies under the guidance of C.W., with help from J.J. and C.C. H.W. and Y.Y. performed operando DEMS measurements. J.J. and C.C. prepared the scheme. Y.Y., S.L. and S.Y. wrote the manuscript under the supervision of P.Y. All authors revised and approved the manuscript.
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Extended data figures and tables
Extended Data Fig. 1 Atomic-scale microstructures and chemical compositions of a family of Cu NP ensembles (7, 10, 18 nm).
(a–b) HAADF-STEM image and EELS composite map of fresh 7 nm NPs with metallic Cu core (red) and ~2 nm oxide shell (green), which were oxidized to Cu2O NPs after brief air exposure (Supplementary Fig. 3). (c) STEM image of 10 nm Cu@Cu2O NPs with multi-domain Cu core close to the [110] zone axis surrounded by the Cu2O shell with characteristic d-spacings of Cu2O{111} (2.5 Å). (d) STEM-EELS composite map of 10 nm Cu@Cu2O NPs with ~2 nm oxide shell. (e–f) STEM image of 18 nm Cu@Cu2O NPs and EELS composite map showing the ~2 nm oxide shell.
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Yang, Y., Louisia, S., Yu, S. et al. Operando studies reveal active Cu nanograins for CO2 electroreduction. Nature 614, 262–269 (2023). https://doi.org/10.1038/s41586-022-05540-0
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DOI: https://doi.org/10.1038/s41586-022-05540-0
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