Superior Oxygen Exchange Kinetics on Bi₂O₃-Based Mixed Conducting Composites

The kinetics of oxygen exchange dictate the rate of redox reactions, which is crucial for electrochemical-based sustainable technologies. In this study, we use isotope exchange pulse responses to elucidate the oxygen exchange mechanism for (Bi_0.8Tm_0.2)₂O_3-δ (BTM)-(La_0.8Sr_0.2)_0.99MnO_3-δ (LSM) composites. With an optimized composition and microstructure, these composites can achieve polarization resistances below 0.01 Ω·cm² at 700 °C. Analysis of the oxygen exchange rate, , by splitting it into elementary processes using the serial two-step scheme, demonstrates that both the dissociative adsorption and incorporation of oxygen are accelerated in BTM-LSM compared to the parent phases. Dissociative adsorption of molecular oxygen is rate-limiting below 900 °C in the range 0.002-0.05 atm O₂ and below 850 °C in 0.21 atm O₂. Cation interdiffusion or changes in the electronic structure at the interface between the two materials create an electrocatalytically active region spanning 1-40 nm around the BTM-LSM phase boundary. Oxygen exchange coefficients within this region were estimated to be 2-3 orders of magnitude higher compared to those of the entire composite surface. We propose two potential pathways for oxygen exchange in BTM-LSM, with calculated p _O dependencies for each rate-determining step (rds). The p _O dependency of reveals that molecular oxygen is involved in the rds.