Ruddlesden-Popper-based lanthanum cuprate thin film cathodes for solid oxide fuel cells: Effects of doping and structural transformation on the oxygen reduction reaction

Highly textured, c-axis oriented thin films of undoped, Ba-doped, and Sr-doped La₂CuO₄ are successfully prepared on YSZ (100) substrates by using pulsed laser deposition. Intriguingly, the films undergo a structural transformation from T′(square-planar) to T (octahedral) crystal structure with partial substitution of Ba and Sr ions on La site. Meanwhile, the addition of both Ba and Sr dopants lead to reducing in polarization resistance and alternative kinetics of oxygen reduction reaction (ORR), hereinto La_1·8Ba_0·2CuO₄ film presents superior electrochemical properties because it can accommodate much more oxygen vacancies than the other two films. First-principles calculations reveal that much lower O-defect formation energy originate fundamentally from the increase of Cu–O bond length along c-axis orientation after structural transformation from T′-phase to T-phase. These findings unveil the relationship between the structural transformation and ORR activity, and provide a novel approach to rational design film cathodes for higher electrochemical performance.