Preparation and oxygen evolution reaction on nanoporous semi-transparent La0.8Sr0.2CoO3 coatings: stability and mechanism in neutral medium

Abstract

For the prospective use in oxygen evolution reaction, the semi-transparent thin film of La0.8Sr0.2CoO3 (LSCO), was deposited on fluorine-doped tin oxide coated glass substrate as an electrocatalyst, by using sol–gel method of synthesis followed by spin coating. Detailed characterization explains the crystallinity, homogeneity and nano porosity of the film. Films are conducting with low sheet resistance and high carrier concentration. Electrochemical measurements in 0.1 M phosphate buffer solution (pH 7.4) confirms the evolution of oxygen which starts at 1.51 V vs RHE with an overpotential value of 280 mV and Tafel slope value of 104 mv/dec in neutral medium (0.1 M phosphate buffer), which remain stable for a long time. LSCO is a well-known material for OER in basic medium, as demonstrated in many literature studies. However, this study demonstrates its electrocatalytic activity in neutral medium and how the surface of material changes after some time. Catalyst is subjected to the stability test for ~ 22 hours, and it is observed that stability is good. Post electrochemical characterization using XRD and XPS indicates that the bulk lattice remains intact, however breakdown of the surface lattice structure produces separate oxides. Briefly, reduced cobalt oxide and oxidised strontium species form on the surface after electrocatalysis. The reduction is well correlated with the depletion of lattice oxygen from the La0.8Sr0.2CoO3 compound, depicting its role in the OER process. The assumption that cobalt ions play a decisive role in the electrochemical reaction is also established from XPS studies.