Acidity of surface-infiltrated binary oxides as a sensitive descriptor of oxygen exchange kinetics in mixed conducting oxides

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. Improving the kinetics of O2 reduction on oxide surfaces is critical in many energy and fuel conversion technologies. Now, the authors demonstrate that the acidity of infiltrated surface oxides can serve as a descriptor of the oxygen surface exchange rate on mixed conducting oxides.