A novel composite oxygen electrode: PrBaCo2O5+δ combined with negative thermal expansion oxide applied to reversible solid oxide cells

Abstract

The thermal expansion coefficient (TEC) of Co-based layered perovskite electrodes is about twice than that of common electrolytes, and this thermal mismatch between electrode and electrolyte leads to the delamination and cracking of electrode. To solve this problem thoroughly, a strategy of introducing negative thermal expansion (NTE) material is proposed. The average linear thermal expansion coefficient of PrBaCo2O5+δ (PBC) decreases significantly from 22.3 × 10−6 K−1 to 12.2 × 10−6 K−1 when compounds with 50 wt% NdMnO3-δ (NM). The results of multi physical field coupling calculation show that the introduction of NTE oxide can reduce the residual stress of oxygen electrodes and electrolytes, which decreases the trend of electrodes damaged by thermal stress. The composite electrode (PBC-NM) shows excellent electrocatalytic activities and reversible cycle performance. The peak power densities (PPDs) of the cell with PBC decreases from 1.4 to 0.48 W cm−2 (65.7% decrease) after 20 thermal cycles, while the one of PBC-NM-based cell decreases from 1.55 to 1.25 W cm−2 (19.4% decrease). Electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and distribution of relaxation time (DRT) analysis show that the improvement of thermal cycle stability of SOFC can be attributed to the ideal thermal matching between electrolyte and oxygen electrode.