Tuning the Spin State in LaCoO₃ Thin Films for Enhanced High-Temperature Oxygen Electrocatalysis

Abstract

The slow kinetics of oxygen surface exchange hinders the efficiency of high-temperature oxygen electrocatalytic devices such as solid oxide fuel cells and oxygen separation membranes. Systematic investigations of material properties that link to catalytic activity can aid in the rational design of highly active cathode materials. Here, we explore LaCoO thin films as a model system for tuning catalytic activity through strain-induced changes in the Co spin state. We demonstrate that Raman spectroscopy can be used to probe the Co-O bond strength at different temperatures to determine the relative spin occupancies of LaCoO. We find that strain can be used to reduce the spin transition temperature and promote the occupation of higher spin states that weaken the Co-O bond. The decrease in Co-O bond strength and increased spin moment of the thin films result in significant enhancements of the oxygen surface exchange kinetics by up to 2 orders of magnitude.

“Stretching” the energy landscape of oxides—Effects on electrocatalysis and diffusion

“…92 They probed the Co-O bond strength by Raman spectroscopy at different temperatures to determine the relative spin occupancies of LaCoO 3 . Strain in the LCO fi lms reduced the spin transition temperature ( Figure 7 ) and promoted the occupation of higher spin states.…”

When two become one: An insight into 2D conductive oxide interfaces

“…In the case of oxygen ionic conductors, however, conduction mechanisms at the interfaces are complicated by the nature of the oxygen vacancies, which are substitutional Schottky-like defects, as well as by the chemistry of the materials, where dopants and other elements easily segregate at the interface imposing local "extrinsic" factors to the conduction mechanisms. These important factors are widely proved in the case of solid-gas interfaces (not treated here), where structural strain, high vacancies concentration and elemental segregation can, e.g., greatly affect catalytic performances of the materials by changing gas sorption-desorption and surface diffusion mechanisms [76][77][78]. On the other hand, solid-solid interfaces can present a wide range of features and properties and in some cases these factors can result beneficial for applications as in thin film-based ionic devices [79].…”

Edge dislocation slows down oxide ion diffusion in doped CeO2 by segregation of charged defects

“…This high density of dislocations makes the study of their effect on the properties of the material of paramount importance. The elastic strain effects in oxides have been extensively studied for transport [9][10][11] , (electro)catalytic activity [12][13][14] and multiferroic properties 15,16 . On the other hand, only a few recent studies directly assessed the potential role of dislocations on the electrical 17,18 , magnetic 19 and chemical 20,21 properties of oxides, probably because of the intrinsic difficulty in studying these extended defects one at a time with high spatial resolution.…”