Boosting the ORR kinetics of protonic ceramic fuel cells via surface decoration using nonreactive insulators

Abstract

As a promising energy conversion device, protonic ceramic fuel cells (PCFCs) are highly efficient, with negligible environmental impact and low cost, yet they are mainly restricted by a sluggish proton involved oxygen reduction reaction (p-ORR). In this study, we demonstrate that surface decoration with nonreactive insulators, including carbonates and oxides, is an efficient method that can be used to regulate the electronic structure of cathodes and to modify the p-ORR kinetics using DFT calculations and experimental investigations. Insulators with work functions lower than that of the PrBaFe₂O_5+δ (PBF) cathode, such as Y₂O₃ and BaCO₃, can accelerate oxygen reduction reaction kinetics, yet those with higher work functions, such as Al₂O₃, retard ORR kinetics. A Y₂O₃-decorated surface exhibited a 293% enhancement in k_chem at 650 °C compared to pristine PBF, while a surface modified by Al₂O₃ demonstrated a 59% reduction. Bader charge analysis revealed that the PBF surface gained electrons from a Y₂O₃ cluster, yet it donated electrons to an Al₂O₃ cluster, which should be the main reason for the modified k_chem. Area specific resistance (ASR) measurements further indicate that excess insulators on the cathode surface will decay the ORR kinetics due to the severe shrinkage of the active surface, which exceeds the positive effect from work functions.