Strain influence on the oxygen electrocatalysis of the (100)-oriented epitaxial La₂NiO_4+δ thin films at elevated temperatures

Ruddlesden-Popper materials such as La₂NiO_4+δ (LNO) have high activities for surface oxygen exchange kinetics promising for solid oxide fuel cells and oxygen permeation membranes. Here we report the synthesis of the (100)_tetragonal-oriented epitaxial LNO thin films prepared by pulsed laser deposition. The surface oxygen exchange kinetics determined from electrochemical impedance spectroscopy (EIS) were found to increase with decreasing film thickness from 390 to 14 nm. No significant change of the surface chemistry with different film thicknesses was observed using ex situ auger electron spectroscopy (AES). Increasing volumetric strains in the LNO films at elevated temperatures determined from in situ high-resolution X-ray diffraction (HRXRD) were correlated with increasing surface exchange kinetics and decreasing film thickness. Volumetric strains may alter the formation energy of interstitial oxygen and influence on the surface oxygen exchange kinetics of the LNO films.