Cathode water management towards improved performance of protonic ceramic fuel cells

Over protonic ceramic fuel cells (PCFCs) cathode, both oxygen reduction reaction (ORR) and hydration reaction happen. To maximize the performance, the cathode requires sufficient proton conductivity for facilitating water formation and large number of active sites and high intrinsic activity for catalyzing ORR. Herein, we demonstrate hydration reaction and ORR over PCFC cathode can be optimally balanced through controlling the air flow rate, which adjusts the equilibrium water and oxygen content in the surrounding atmosphere of the cathode. Then the suitable proton uptake can enhance the proton conductivity of the cathode without negatively affecting ORR. The different characteristics of various cathode materials suggest their different optimal operation conditions. Specifically, the optimal performance of SrTi0.1Fe0.9O3-δ, Ba0.5Sr0.5Co0.8Fe0.2O3-δ and BaCo0.4Fe0.4Zr0.1Y0.1O3-δ cathodes in PCFCs at 600 °C is reached at different water content in the air atmosphere of 472, 592 and 735 mW cm−2, respectively, showing increased peak power density (PPD) of 13%, 10% and 6% of the corresponding cells as compared to that operating near static air atmosphere. Our study reveals the important environmental demands of PCFC cathode during the operation and provides useful guidance for the further performance optimization. [Display omitted] •Hydration reaction and ORR over PCFC cathode can be balanced by air flow rate.•Optimal concentration of water vapor is different for each cathode material.•Suitable proton uptake can enhance conduction of H+ without adverse effect on ORR.