Abstract
Improving the kinetics of O2 reduction on oxide surfaces is critical in many energy and fuel conversion technologies. Here we show that the acidity scale for binary oxides is a powerful descriptor for tuning and predicting oxygen surface exchange kinetics on mixed conducting oxides. By infiltrating a selection of binary oxides from strongly basic (Li2O) to strongly acidic (SiO2) onto the surface of Pr0.1Ce0.9O2-δ samples, it was possible to vary the chemical surface exchange coefficient kchem by 6 orders of magnitude, with basic oxides such as Li2O increasing kchem by nearly 1,000 times, with surface concentrations as low as 50 ppm impacting kchem. Strikingly, although the pre-exponential of kchem scales linearly with the acidity of the infiltrated binary oxide, there is nearly no change in the activation energy. The origin of these dramatic changes is proposed to arise from the systematic increase in electron concentration at the Pr0.1Ce0.9O2-δ surface with the decreasing acidity of the infiltrated binary oxide.
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Data availability
The datasets of conductivity relaxation analysed during the current study are available in the source files of this manuscript. All other data are available within the paper and its Supplementary Information files. Source data are provided with this paper.
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Acknowledgements
This research was primarily supported by the US Department of Energy (DOE), National Energy Technology Laboratory (NETL), Office of Fossil Energy under Award no. DE-FE0031668—Self-Regulating Surface Chemistry for More Robust Highly Durable Solid Oxide Fuel Cell Cathodes. Supplementary support was provided by the US DOE, Office of Science, Basic Energy Sciences (BES), under Award no. DE-SC0002633—Chemomechanics of Far-From-Equilibrium Interfaces (XPS studies). G.F.H. acknowledges support from a Kakenhi Grant-in-Aid for Encouragement of Young Scientists (B) Award (no. JP18K13992) (TEM studies). Thanks go to A. Grimaud and D. Kalaev for helpful discussions.
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Contributions
C.N. suggested the original idea. C.N. and H.L.T. designed the experimental protocol. C.N. prepared the samples, built the experimental set-up and performed the conductivity relaxation measurements. G.F.H. prepared the lamellae for TEM, performed the TEM measurements and computed the defect model used to interpret the results. C.T. prepared and measured the samples by XPS. C.T. and B.Y. performed the analysis of the XPS measurements and interpreted the results. T.D. performed the Raman spectroscopy measurements and interpreted the results. H.L.T. supervised the work and provided guidance throughout the project. C.N. and H.L.T. wrote the manuscript. All the co-authors discussed the results and helped to revise the manuscript.
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Supplementary Information
Supplementary Notes 1–9, Figs. 1–11, Equations 1–8 and Table 1.
Source data
Source Data Fig. 3
Unprocessed conductivity relaxation profiles for all infiltrated samples.
Source Data Fig. 4
Unprocessed conductivity relaxation profiles for each increment of Li infiltration.
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Nicollet, C., Toparli, C., Harrington, G.F. et al. Acidity of surface-infiltrated binary oxides as a sensitive descriptor of oxygen exchange kinetics in mixed conducting oxides. Nat Catal 3, 913–920 (2020). https://doi.org/10.1038/s41929-020-00520-x
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DOI: https://doi.org/10.1038/s41929-020-00520-x
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