Electrochemical performance of continuously gradient composite cathode fabricated by electro-static slurry spray deposition

Abstract

The cobalt-based cathode, LSCF, BSCF and SSC, have high thermal expansion coefficients, which cause poor thermal compatibility with electrolytes and limited cell performance. In this work, a continuously gradient Sm0.5Sr0.5CoO3−δ (SSC) – BaCe0.7Zr0.2Y0.1O3−δ (BCZY) composite cathode was developed for BCZY electrolyte based fuel cells by electrostatic spray slurry deposition (ESSD). In the deposited cathode the content of BCZY gradually decreased and that of SSC gradually increased in the direction away from the electrolyte–cathode interface. The single cell, consisting of a BCZY–NiO anode substrate, a BCZY electrolyte and a compositionally gradient SSC-BCZY cathode layer, was assembled and tested from 550 to 700 °C under humidified hydrogen atmosphere (∼3% H2O) and static air as an oxidant. The cross-sectional morphology of the cathode was examined by energy dispersive X-ray (EDX) analysis. The comparison of electrochemical performances between various cathode configurations was conducted to demonstrate the effect of gradient cathode. The power density and impedance spectra indicate that the optimized cathode structure greatly improves the polarization resistance and ohmic resistance. The results suggest that the migration of protons to triple phase boundaries (TPBs) and the surface diffusion of O− might be enhanced in the gradient SSC–BCZY composite cathodes.