Abstract
Electrolysis of CO2 in molten salts promises efficient carbon capture, but the underlying reaction mechanisms remain incompletely understood, as research thus far has been limited by a lack of tools for operando investigations. Here, we use a high-temperature operando Raman spectroelectrochemical system to look for signatures of reaction intermediates and study the evolution of carbon structures over electrolysis time. The analysis reveals the existence of O22− concurrently with the deposition of carbon on Au, W, Inconel, and Ni electrode materials, pointing to a common reaction mechanism with O22− as an intermediate. Secondly, the G peak of the as-deposited carbon experiences a noticeable blue-shift as the material is cooled down and purified, suggesting either a growth in crystallite size even after the electrolysis is stopped or lithium deintercalation. Elucidating the cathodic carbon deposition mechanism could help create greater value-added products and increase the economic viability of carbon capture.
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Additional data on the determination of the electrochemical window, Raman signatures and their determination, deconvolution of the carbon region of the Raman spectra, additional Raman spectroelectrochemical data on Ni, Au, and W electrodes and data on the temperature-dependant G peak shift in CO2-derived carbon, surface morphology of the deposited carbons, validation of the quasi-reference electrode potential scale and determination of tungsten content in the electrolyte after electrolysis are given in the Supplementary information. Source data are provided as a Source Data file. Source data are provided with this paper.
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Acknowledgements
This work was funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under contract No. DE-AC02-05-CH11231 (MINES project: The Science of Direct MINeral to Energy Storage Synthesis, FWP: FP00014914)—S.R., M.L.W., and R.O.S. This work was supported by the Estonian Research Council grants PUTJD1233—S.R.; EAG271, PSG1017, TK228U8, and TEM-TA96—S.R., K.K. Sander Ratso acknowledges the support of the Baltic-American Freedom Foundation. We thank Dr. Finn Babbe (LBL) for helpful discussions and his assistance with the spectroelectrochemical measurements, Dr. Valdek Mikli for the SEM measurements, and Dr. Jekaterina Kozlova for the TEM measurements.
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S.R.: Conceptualization, methodology, formal analysis, investigation, writing—original draft, writing—review & editing, visualization, funding acquisition, and resources; M.L.W.: Writing—review & editing, funding acquisition, and resources; K.K.: Methodology, formal analysis, investigation, and writing—review & editing; R.O.S.: Conceptualization, methodology, formal analysis, writing—review & editing, visualization, supervision, project administration, funding acquisition, and resources.
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Ratso, S., Whittaker, M.L., Kaare, K. et al. Operando spectroelectrochemical identification of peroxide intermediate in molten carbonate CO2-to-carbon electroreduction. Nat Commun (2026). https://doi.org/10.1038/s41467-026-70977-0
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DOI: https://doi.org/10.1038/s41467-026-70977-0
