Selective high-temperature CO2 electrolysis enabled by oxidized carbon intermediates

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Abstract

High-temperature CO2 electrolysers offer exceptionally efficient storage of renewable electricity in the form of CO and other chemical fuels, but conventional electrodes catalyse destructive carbon deposition. Ceria catalysts are known carbon inhibitors for fuel cell (oxidation) reactions; however, for more severe electrolysis (reduction) conditions, catalyst design strategies remain unclear. Here we establish the inhibition mechanism on ceria and show selective CO2 to CO conversion well beyond the thermodynamic carbon deposition threshold. Operando X-ray photoelectron spectroscopy during CO2 electrolysis—using thin-film model electrodes consisting of samarium-doped ceria, nickel and/or yttria-stabilized zirconia—together with density functional theory modelling, reveal the crucial role of oxidized carbon intermediates in preventing carbon build-up. Using these insights, we demonstrate stable electrochemical CO2 reduction with a scaled-up 16 cm2 ceria-based solid-oxide cell under conditions that rapidly destroy a nickel-based cell, leading to substantially improved device lifetime.

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Fig. 1: Model electrodes employed and measurements of carbon formation/oxidation as the overpotential is varied.
Fig. 2: Surface carbon species observed with APXPS and SEM.
Fig. 3: Evolution of surface carbon species as overpotential is varied.
Fig. 4: Proposed reaction mechanism and calculated energetics for carbon formation on nickel and ceria surfaces.
Fig. 5: Comparison of the abilities of scaled-up SOCs with Ni-YSZ versus ceria electrodes to suppress carbon deposition during CO2 electrolysis.

Data availability

Data underlying the study can be found at Figshare57 (APXPS and cell testing) and https://www.catalysis-hub.org/publications/SkafteSelective2019 (DFT)58.

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Acknowledgements

We thank L. Zhang for SEM assistance, A. Lyck Smitshuysen for assistance with preparing the large-format cells, R. M. Ortiz de la Morena for 3D modelling and rendering the wind turbine in Fig. 5, and H. Bluhm for assistance at beamline 11.0.2. This research used resources of the Advanced Light Source, which is a US Department of Energy Office of Science User Facility, under contract no. DE-AC02-05CH11231. The authors gratefully acknowledge financial support from Haldor Topsoe A/S, Innovation Fund Denmark, the Danish Agency for Science, Technology and Innovation (grant no. 5176-00001B and 5176-00003B) and Energinet.dk under the project ForskEL 2014-1-12231. The work at Stanford was supported by the National Science Foundation CAREER Award (1455369). M.B. acknowledges support from the US Department of Energy, Chemical Sciences, Geosciences, and Biosciences (CSGB) Division of the Office of Basic Energy Sciences, via grant DE-AC02-76SF00515 to the SUNCAT Center for Interface Science and Catalysis. We thank J. Nørskov and T. Bligaard at the SUNCAT Center for Interface Science and Catalysis for hosting T.L.S. and C.G. All calculations in this work were performed with the use of the computer time allocation (m2997) at the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the US Department of Energy under contract no. DE-AC02-05CH11231.

Author information

T.L.S., C.G. and W.C.C. designed the experiments. T.L.S. carried out the spectroscopic and electrochemical analysis. M.L.M., L.M., E.S., S.S. and T.L.S. manufactured samples. T.L.S., Z.G. and C.G. carried out preliminary experiments and sample characterization. Z.G., T.L.S., C.B.G., M.M., C.G., M.L.M. and E.J.C. carried out the XPS experiments. M.B. and M.G.-M. designed and conducted the DFT calculations. T.L.S. and C.G. carried out the large-format cell experiments. T.L.S., C.G., W.C.C., M.B., M.G.-M., J.A.G.T., Z.G. and M.M. contributed to writing the article. C.G. initiated the collaborative project. W.C.C. and C.G. supervised and guided the work.

Correspondence to Michal Bajdich or William C. Chueh or Christopher Graves.

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Supplementary Notes 1–3, Figs. 1–21, Tables 1–5 and refs.

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