Electrochemical performance and stability of cobalt-free Ln1.2Sr0.8NiO4 (Ln=La and Pr) air electrodes for proton-conducting reversible solid oxide cells

Cobalt-free Ruddlesden-Popper structured Ln1.2Sr0.8NiO4 (Ln = La and Pr) have been synthesized by a modified Pechini method, moreover, their thermal and electrochemical properties as well as performance of cells with proton-conducting electrolytes have been investigated. Experimental results reveal that the thermal expansion coefficients of Ln1.2Sr0.8NiO4 are close to those of Ba(Ce,Zr)O3-based proton conductors. The polarization resistances of symmetrical cells with La1.2Sr0.8NiO4 (LSN) and Pr1.2Sr0.8NiO4 (PSN) electrodes are as low as 0.15 and 0.23 Ω cm2 at 700 °C, respectively. Besides, Ln1.2Sr0.8NiO4 can remain stable structure over 100 h in humidified air (20 vol% H2O) at 800 °C. Furthermore, proton-conducting reversible solid oxide cells (PC-RSOCs) with LSN and PSN air electrodes exhibit maximum power densities of 0.46 and 0.35 W cm−2 in solid oxide fuel cell mode at 700 °C, respectively. Meanwhile, the same cells achieve current densities as high as 1.37 and 1.12 A cm−2 in solid oxide electrolysis cell mode at 700 °C with a given voltage of 1.3 V, respectively. In addition, both of two cells with LSN and PSN air electrodes present acceptable short-term stability under reversible operation condition. These encouraging results suggest that Ln1.2Sr0.8NiO4 could be suitable candidates of air electrodes in intermediate-temperature PC-RSOCs.