Enhanced Electrocatalytic Activity and Surface Exsolution in PrOx-Substituted Cerium Gadolinium Oxide

The electrocatalytic activity of Pr-substituted cerium gadolinium oxide (CGO) was examined to assess its suitability as a composite air electrode in solid oxide cells. The solid-state reaction of CGO and Pr6O11 yielded fluorite-type solid solution, (Ce0.9Gd0.1)1–xPrxO2−δ (x = 0, 0.17 and 0.33), with an increased lattice parameter. Electrochemical tests of electrolyte-supported cells with CGO-PrOx and LSCF-CGO-PrOx electrodes exhibited that the PrOx addition significantly improves the electrical conductivity and electrocatalytic activity for oxygen reduction reaction (ORR). In-depth characterization showed that the improved ionic and electrical conductivities of CGO-PrOx are associated with high concentration of oxygen vacancies created by replacement of Ce4+ ions with Pr3+ ions. TEM analysis revealed that annealing of CGO-PrOx results in the exsolution of PrOx nanoparticles, indicating local lattice strain around Pr3+ and eventually their outward migration. TPD, TPR, and TPO measurements further demonstrated that CGO-PrOx has greater oxygen reduction reaction (ORR) activity at low temperatures (400–600 °C) when compared to CGO. These findings suggest the high potential of Pr-substituted CGO for low-temperature solid oxide cell applications.