High Performance and Stability Enabled by Tuning the Component Thermal Expansion Coefficients of a Proton-Conducting Solid Oxide Cell Operating at High Steam Concentration

The solid oxide cell (SOC) based on a proton-conducting electrolyte is promising to play an important role in large-scale energy storage and hydrogen production. However, its development is hindered by performance degradation caused by the mismatch in thermal expansion coefficients (TECs) between the electrolyte and the oxygen electrode. Although there is work on reducing TECs of the oxygen electrode, it is difficult to find proper materials having a low TEC while maintaining a high performance. In this paper, we propose a new path to solve this problem: increasing the TEC of the electrolyte. We demonstrate that doping Fe into BaZr0.3Ce0.5Y0.1Yb0.1O3-delta (BZCYYb) can increase the TEC from 10.3 x 10-6 K-1 of BZCYYb to 13.4 x 10-6 K-1 of BaZr0.3Ce0.48Fe0.02Y0.1Yb0.1O3-delta (BZCYYbF). Fe doping also enhances the sinterability, electrochemical performance, and stability of the electrolyte. Meanwhile, we find that doping Fe into the oxygen electrode material PrNi0.5Co0.5O3-delta (PNC) decreases the TEC from 19.2 x 10-6 K-1 of PNC to 17.4 x 10-6 K-1 of PrNi0.4Co0.4Fe0.2O3-delta (PNCF). The improved stability of the SOC with the BZCYYbF electrolyte and the PNCF oxygen electrode is verified for steam electrolysis under a high steam partial pressure, 50%. Such a cell operates stably at a current density of 1.76 A cm-2 under 1.30 V and 700 degrees C for 150 h.