A functionally graded cathode for proton-conducting solid oxide fuel cells

The cobalt-containing cathode materials facilitate the activity of oxygen reduction, but they also suffer from problems like high thermal expansion coefficients, which cause poor thermal compatibility with electrolytes and limited performance stability. In this work, a functionally graded PrBaCo2O5 (PBCO) cathode is developed for solid oxide fuel cells (SOFCs) based on proton-conducting BaCe0.7Zr0.1Y0.2O3−δ (BCZY) electrolyte. The compositions of the cathodes are gradually changed from a material that is active for oxygen reduction and more compatible with the electrolyte BCZY to another material that is more conductive for current collection. The single cells have high resistance to thermal shock, showing well-combined cathode-electrolyte interface after 60 times of thermal cycles. Meanwhile, a maximum power density of 588 mW cm−2 and a low polarization resistance of 0.08 Ω cm−2 is achieved at 700 °C, respectively. The impedance spectra indicate that the optimized cathode structure greatly improves the polarization resistance while ohmic resistance is mainly determined by the conductivity and thickness of electrolyte. The results demonstrate that this configuration not only buffers the TEC mismatch but also optimizes the cathode structure for oxygen reduction reaction.

► A functionally graded PrBaCo2O5 (PBCO) layered perovskite cathode was developed for solid oxide fuel cells. ► The as-prepared fuel cell with tri-layer graded cathode showed excellent thermal stability after quick heating-cooling cycles. ► The fuel cells showed the low polarization resistances and high power densities.