Obtenção e caracterização de compósitos com condutividade tripla para uso como eletrodo de células a combustível

Abstract

Solid oxide fuel cells (SOFCs) have emerged as a viable alternative to replace fossil fuels in the generation of clean energy with low environmental impact. The use of materials with perovskite structures in electrodes has gained significant attention, with systems such as BCZY being used in composite forms to achieve triple conductivity. The formation of a BCZY–LCN ceramic composite aims to combine two perovskites with different electrical behaviors to enhance catalytic activity at the electrode and promote triple conductivity in the composite. Through chemical synthesis routes and solid-state reaction, the goal was to obtain a composite with suitable porosity and high electronic, ionic, and protonic conductivity. XRD results indicate that the BCZY and LCN phases were formed during calcination, although secondary phases were observed. After sintering, besides the desired oxide phases, a secondary CeO2 phase was also identified. The PER and ESR composites exhibit porosities ranging between 30% and 45%. Four-point probe measurements confirm the electronic conductivity of LCN, with LCN55 PER showing a conductivity of 137.24 S/cm at 800°C and LCN55 ESR reaching 35.32 S/cm at the same temperature. Four- point measurements also indicate that the composites possess both electronic and ionic conductivity; however, protonic conductivity could not be confirmed. The PER composite exhibits a conductivity of 0.9083 S/cm at 400 °C, while the ESR composite reaches 0.7157 S/cm at 600 °C. Impedance spectroscopy measurements reveal that the material has low total conductivity in a hydrogen atmosphere, with evidence of additional phase formation after exposure to this reducing atmosphere. The PER and ESR composites showed higher polarization resistance when applied to BCZY substrates compared to LCN55 applied on the same substrate. SEM images reveal the presence of rod-like BaCO3 structures in BCZY27 synthesized by the modified Pechini method. The composites exhibit interconnected porosity in the SEM images, while the LCN55 bars did not achieve full densification, showing porosity. In addition, LCN55 PER displays larger grains compared to LCN55 ESR. Good adhesion was observed between the painted electrode (either the composite or pure LCN55) and the BCZY substrate used in the polarization resistance measurements.