Unravelling the role of B-site cation enrichment and Co–Fe exsolution in LaAl_0.90Co_0.05Fe_0.05O₃ on oxygen reduction electrocatalysis

In the present study, we report the exsolution of CoFe nanoalloy nanoparticles from Co and Fe co-doped lanthanum aluminate perovskite oxide, LaAl_0.90Co_0.05Fe_0.05O₃, and assess the perovskite oxide as an oxygen reduction reaction (ORR) electrocatalyst. We optimized both intrinsic and extrinsic material properties of perovskites to achieve good electrocatalytic performance in the kinetic and mass-transfer controlled region. First, we demonstrated that the near surface segregation of B-site cation (Co) under a reducing environment at low temperature (500 °C), believed to represent the initial stage of exsolution, led to high ORR activity in the mass-controlled region, with specific and mass activities of 4.9 mA cm⁻² and 37.5 A/g (@0.4 V versus reversible hydrogen electrode, RHE), respectively. Second, reducing the particle size of perovskite oxide increased surface exposure to the reducing environment promoting the CoFe nanoalloy particle exsolution. The results demonstrate that cation enrichment in the subsurface region, near grain boundaries contributes more effectively to ORR activity than exsolution in the form of nanoparticles in the perovskite oxide composition. Nevertheless, achieving fast charge transfer-kinetics without the use of precious metals still remains a challenge with lanthanum aluminates, as indicated by onset potentials of 0.84 and 0.81 V (versus RHE) for the pristine and reduced perovskite oxide, respectively. Notably, the impregnation of perovskite oxide with 0.2 wt. % Pt followed by heat treatment in the reducing atmosphere at 500 °C increased the onset potential to 0.9 V. Overall, this study suggests that the non-precious metal-doped lanthanum aluminate, LaAl_0.90Co_0.05Fe_0.05O₃, exhibits strong electrocatalytic activity and is further enhanced through impregnation treatment.