Details on oxygen surface exchange mechanism over Pr _1.6 Ca _0.4 Ni _1−y Cu _y O _4+δ solid oxide fuel cell/electrolyzer air electrodes

In the design of solid oxide fuel cell/electrolyzer air electrodes, the oxygen mobility and surface reactivity are of paramount importance. In this study, the oxygen surface heteroexchange rate is examined for a series of promising electrode materials, Pr1.6Ca0.4Ni1−yCuyO4+δ (y = 0.0–0.4). The investigation encompasses the relationship between this rate and the structural, surface, and electrochemical properties. Single-phase materials synthesized by a nitrate combustion technique using glycerol as a fuel possess an orthorhombic structure. The oxygen surface reactivity is studied by the temperature-programmed isotope exchange of oxygen with 18O2 in a flow reactor. The values of the oxygen heteroexchange rate (R*) and surface exchange constant (k*) are acquired using mathematical modeling. The isotope exchange between the gas oxygen and the sample surface occurs primarily via the R2-type of exchange mechanism, i.e., the simultaneous exchange of two atoms of the oxygen molecule with two atoms of oxygen in the sample surface. The process is limited by surface exchange of oxygen characterized by high values of surface exchange constant (up to ~ 10–5 cm/s at 700 °C). The best characteristics are achieved for the Pr1.6Ca0.4Ni1−yCuyO4+δ samples, y = 0.0–0.2. There is a correlation of the oxygen exchange kinetic parameters (surface exchange constant, tracer diffusion coefficient) with the electrochemical properties of the electrodes according to the Adler–Lane–Steele model.