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Constructing a pathway for mixed ion and electron transfer reactions for O2 incorporation in Pr0.1Ce0.9O2−x

Abstract

In interfacial charge-transfer reactions, the complexity of the reaction pathway increases with the number of charges transferred, and becomes even greater when the reaction involves both electrons (charge) and ions (mass). These so-called mixed ion and electron transfer (MIET) reactions are crucial in intercalation/insertion electrochemistry, such as that occurring in oxygen reduction/evolution electrocatalysts and lithium-ion battery electrodes. Understanding MIET reaction pathways, particularly identifying the rate-determining step (RDS), is crucial for engineering interfaces at the molecular, electronic and point defect levels. Here we develop a generalizable experimental and analysis framework for constructing the reaction pathway for the incorporation of O2(g) in Pr0.1Ce0.9O2−x. We converge on four candidates for the RDS (dissociation of neutral oxygen adsorbate) out of more than 100 possibilities by measuring the current density–overpotential curves while controlling both oxygen activity in the solid and oxygen gas partial pressure, and by quantifying the chemical and electrostatic driving forces using operando ambient pressure X-ray photoelectron spectroscopy.

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Fig. 1: Examples of MIET reactions.
Fig. 2: Electrochemical measurement results.
Fig. 3: Experimental set-up and evolution of surface electron concentration and surface potential with overpotential.
Fig. 4: Reaction orders for OIR.
Fig. 5: Obtaining reaction stoichiometric coefficients (νV,i and νe,i) by analysing λ.
Fig. 6: Reaction mechanism.

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Data availability

Source data that support the findings of this study are available from the corresponding author on request.

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Acknowledgements

This work was supported by the National Science Foundation under award no. 1336835. MIT researcher was supported by grant DE SC0002633 funded by the US Department of Energy, Office of Basic Science. The Advanced Light Source was supported by the Director, Office of Science, Office of Basic Energy Sciences and the Division of Chemical Sciences, Geosciences, and Biosciences of the US Department of Energy at the Lawrence Berkeley National Laboratory under contract no. DE-AC02-05CH11231. We thank C.-C. Chen from Stanford University and Q. Lu from Oak Ridge National Laboratory for critical reading of the manuscript and helpful discussions on XAS. We thank Q. Xu and W. Zhong from Tsinghua University for helpful discussions on data visualization.

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D.C. designed the experiment. Z.G. derived the general microkinetic model for MIECs and D.C. adapted the model for this study. D.C., Z.G. and D.Z. performed the experiments. S.N., L.T., E.C. and H.B. supported the beamline experiments. D.C. analysed the data. D.C., H.L.T. and W.C.C. wrote the manuscript. All authors revised the manuscript. W.C.C. supervised the project.

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Correspondence to William C. Chueh.

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Supplementary Figs. 1–8, Tables 1 and 2, Notes 1–10 and references.

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Chen, D., Guan, Z., Zhang, D. et al. Constructing a pathway for mixed ion and electron transfer reactions for O2 incorporation in Pr0.1Ce0.9O2−x. Nat Catal 3, 116–124 (2020). https://doi.org/10.1038/s41929-019-0401-9

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