Superior Oxygen Exchange Kinetics on Bi2O3-Based Mixed Conducting Composites

Abstract

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_O2 dependencies for each rate-determining step (rds). The p_O2 dependency of reveals that molecular oxygen is involved in the rds.