Strontium influence on the oxygen electrocatalysis of La[subscript 2−x]Sr[subscript x]NiO[subscript 4±δ] (0.0 ≤ x[subscript Sr] ≤ 1.0) thin films

Abstract

Substitution of lanthanum by strontium (Sr) in the A-site of cobalt-containing perovskites can greatly promote oxygen surface exchange kinetics at elevated temperatures. Little is known about the effect of A-site substitution on the oxygen electrocatalysis of Ruddlesden–Popper (RP) oxides. In this study, we report, for the first time, the growth and oxygen surface exchange kinetics of La[subscript 2−x]Sr[subscript x]NiO[subscript 4±δ] (LSNO, 0.0 ≤ x[subscript Sr] ≤ 1.0) thin films grown on (001)[subscript cubic]-Y[subscript 2]O[subscript 3]-stabilized ZrO[subscript 2] (YSZ) by pulsed laser deposition. High-resolution X-ray diffraction analysis revealed that the LSNO film orientation was changed gradually from the (100)[subscript tetra.] (in-plane) to the (001)[subscript tetra.] (out-of-plane) orientation in the RP structure with increasing Sr from La[subscript 2]NiO[subscript 4+δ] (x[subscript Sr] = 0) to LaSrNiO[subscript 4±δ] (x[subscript Sr] = 1.0). Such a change in the LSNO film orientation was accompanied by reduction in the oxygen surface exchange kinetics by two orders of magnitude as shown from electrochemical impedance spectroscopy results. Density functional theory (DFT) calculations showed that Sr substitution could stabilize the (001)[subscript tetra.] surface relative to the (100)[subscript tetra.] surface and both Sr substitution and increasing (001)[subscript tetra.] surface could greatly weaken adsorption of molecular oxygen in the La–La bridge sites in the RP structure, which can reduce oxygen surface exchange kinetics.