Effect of synthesis route on electrochemical performance of PrBaCo2O5+δ cathode for IT-SOFC application

Reduction in solid oxide fuel cells operating temperature to intermediate range (500–700°C) causes significant increase in the electrode polarization, especially at cathode due to high activation energy for oxygen reduction reaction (ORR). In fact, electrochemical performance of cathode significantly depends on the synthesis routes owing to the change in microstructures. PrBaCo2O5+δ double-perovskite cathode is synthesized using four different synthesis routes viz. combustion, sol–gel, mechanochemical alloying and solid-state reaction to obtain desired microstructure in view of optimum electrochemical performance. PrBaCo2O5+δ prepared with different routes crystalizes into tetragonal structure with crystallite size in the range of 48–64 nm. Maximum electronic conductivity (σdc = 178 S cm–1 at 700°C) and minimum polarization resistance (Rp = 0.112 Ω cm2 at 700°C) along with minimum Ea (0.51 eV) for combustion synthesized PrBaCo2O5+δ are attributed to its minimum effective particle size (382 nm), grain size and optimum porosity. Nanocrystallites not only improve sinterability and mechanical strength of cathode but also promotes (large, disordered surface area) chemical and electrochemical processes in it, thereby improve overall electrode performance. Defect equilibria are proposed to understand dependence of σdc and Rp on ({P}_{{mathrm{O}}₂}), temperature and crystallite size. The electrochemical performance of PrBaCo2O5+δ shows that the charge transfer during ORR is the rate-limiting step. Thus, PrBaCo2O5+δ prepared using combustion can be a potential cathode for IT-OFC applications.