Caráter multifuncional de eletrodos à base de cobaltita de cálcio (Ca3Co2O6)

Abstract

This work presents a study focused on the development of cobaltite of calcium Ca3Co2O6 (C326). This material has properties relevant to a range of applications focusing on electrochemical, magnetic and catalytic devices. The ceramic materials were prepared by a synthesis route called Sol Protein Gel. After calcination at 900 °C/2 h, the resulting ceramic powders were evaluated according to the application required in the electrochemical context and electrocatalytic, and so they were named as Solid Oxide Fuel Cells (SOFC) and as an electrocatalyst used in Oxygen Evolution Reaction (OER).The C326-based SOFC electrodes were tested using gadolinium-doped ceria (CGO) electrolyte as substrate. Composite powders of C236/CGO were also used for electrode preparation. In the latter case, commercial CGO powders (C326/CGO-C) and CGO obtained by the Pechini route (C326/CGO-P) were used in the tests. Symmetrical electrodes of C236 and composites were fabricated on a heat-treated dense CGO substrate at temperatures between 950 – 1000 °C. The electrode based on C236 was also made for OER testing on nickel metal foam. Overpotential measures in the OER reactions were carried out in an alkaline medium. Several techniques have been used to evaluate powders and electrodes based on calcium cobaltites and CGO. The structural and microstructural characterizations were performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical tests and catalysts were performed by impedance measurements and scanning voltammetry linear, measured at 800°C. The polarization resistance values were 1.16 Ω cm2 and 0.72 Ω cm2 for C326-1000°C and C326/CGO-C-1000°C, respectively indicating the best performance with the incorporation of Ce0.9Gd0.1O2-δ (CGO). Tests on search to evaluate the C326 as an electrocatalyst showed an overpotential of 426 mV vs. Reversible Hydrogen Electrode (RHE) to generate a current density of 10 mA cm-2 and a tafel slope equal to 128 mV dec-1, classifying it as a good electrocatalyst for OER.