Introducing transition metal cations to promote the oxygen reduction kinetics of double perovskite as SOFC cathode

This study is based on the modification effect and mechanism analysis of transition state metal ions on NdBaCo 1.9 M 0.1 O 5+δ -based (M = Cu, Sc, Co, Ti) double perovskite. Research has shown that introducing a small amount of large radius, low valence Cu ions into Co-based double perovskite will comprehensively improve the electrochemical performance and stability of SOFCs. At 700 °C, NdBaCo 1.9 Cu 0.1 O 5+δ (NBCCu) exhibited the highest surface oxygen exchange coefficient (5.96 × 10 -4 cm s −1 ) and bulk diffusion coefficient (4.74 × 10 -5 cm s −1 ). As a symmetrical cell, the area specific resistance of NBCCu is only 0.041 Ω cm 2 , which is 53.2 % of NdBaCo 2 O 5+δ (NBC). When NBCCu is used as the cathode of a single cell, the maximum power density can reach 1.12 W cm −2 , which is 1.4 times that of NBC-based single cells. According to the distribution of relaxation time results, NBCCu can comprehensively improve the adsorption and dissociation rates of surface oxygen as well as the charge transfer rate. According to the changes in the radius and valence state of transition metal ions, the introduction of Cu ions endows NBCCu double perovskite with a B-site ion reduction mechanism, a large radius ion enhanced free volume mechanism, and a lattice distortion mechanism caused by doping. The synergistic effect of these three mechanisms enhances the electrocatalytic activity of the cathode. Furthermore, compared to NBC-based single cells, NBCCu-based single cells demonstrated more outstanding long-term stability during testing at a constant current of 0.54 A cm −2 for about 110 h at 700 °C. This study provides an effective approach for efficiently screening transition state metal ion doped perovskites to enhance their electrocatalytic activity and stability.