Surface basicity controlled degradation and recoverability of proton conducting perovskites, BaZr_0.8Ce_0.1Y_0.1O_3−δ and Ba_0.5Sr_0.5Ce_0.6Zr_0.2Gd_0.1Y_0.1O_3−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, BaZr_0.8Ce_0.1Y_0.1O_3−δ (BZCY811) with low cerium content and strontium-containing Ba_0.5Sr_0.5Ce_0.6Zr_0.2Gd_0.1Y_0.1O_3−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.