Surface Basicity Controlled Degradation and Recoverability of Proton Conducting Perovskites, BaZr0.8Ce0.1Y0.1O3−δ and Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3−δ, in the Presence of CO2

A fundamental understanding of carbonation kinetics is essential for the development of durable proton conducting electrolysis cells that can electrochemically convert CO2 into fuels. The degradation behavior of two representative proton conducting perovskite materials, BaZr0.8Ce0.1Y0.1O3−δ (BZCY811) with low cerium content and strontium-containing Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3−δ (BSCZGY6211), was studied and analyzed using different solid–gas reaction models. These perovskite compositions are promising candidates for various electrochemical applications where a combination of high conductivity and high stability is required such as for direct CO2 conversion to fuels (or syngas). The kinetic stability of these two compositions under CO2 (and CO) was evaluated using X-ray diffraction, X-ray photoelectron spectroscopy, micro-Raman spectroscopy, CO2 temperature-programmed desorption, and N2 physisorption. Kinetic analysis of the isothermal solid–gas reaction indicated that BZCY811 powders were partially carbonated according to a first-order nucleation/nuclei growth mechanism, in which oxygen vacancies act as active nucleation sites. The degradation was not complete as a protective external carbonate layer was formed, which maintained the internal crystalline structure of BZCY811. In contrast, BSCZGY6211 was kinetically stable in the presence of CO2 with no signs of degradation at high pressures (2.0 MPa). The higher kinetic stability of the latter composition is rationalized in terms of its higher surface acidity.