Manipulation of rare earth on voltage-driven in-situ exsolution process of perovskite cathodes for low-temperature solid oxide fuel cells

The sluggish oxygen reduction reaction (ORR) of cathode materials below 600 °C is one of the greatest obstacles to realizing the operation of low-temperature solid oxide fuel cells (LT-SOFCs). In this study, the ORR activity of rare earth-doped Ln0.2Ba0.8Co0.7Fe0.3O3−δ (Ln = La, Pr, Nd) cathodes below 600 °C is significantly enhanced through the exsolution of highly active nanoparticles driven by applying a negative voltage of 2 V for 150 s. Pr0.2Ba0.8Co0.7Fe0.3O3−δ (PBCF) cathode exhibits an area-specific resistance of ∼ 0.119 Ω cm2 at 550 °C, approximately 1/3 of that for the pristine cathode (∼0.389 Ω cm2). Such improvement is ascribed to the the modification of its surface with high-density and small-size nanoparticles (CoO). Furthermore, the voltage-driven exsolution process can be manipulated by the surface oxygen vacancy concentration induced by rare earth doping. Compared with La- and Nd-doped cathodes, PBCF cathode has higher surface oxygen vacancy concentration, promoting the exsolution of Co in the bulk and resulting in the formation of higher density and smaller size nanoparticles. These enable the PBCF cathode to show the most significant improvement after treatment. This finding may provide a new strategy for the design of high-performance catalysts for LT-SOFCs.