Cobalt-free Ruddlesden-Popper structured Ln(1.2)Sr(0.8)NiO(4) (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 Ln(1.2)Sr(0.8)NiO(4) are close to those of Ba(Ce,Zr)O-3-based proton conductors. The polarization resistances of symmetrical cells with Ln(1.2)Sr(0.8)NiO(4) (LSN) and Pr1.2Sr0.8NiO4 (PSN) electrodes are as low as 0.15 and 0.23 Omega cm(2) at 700 degrees C, respectively. Besides, Ln(1.2)Sr(0.8)NiO(4) can remain stable structure over 100 h in humidified air (20 vol% H2O) at 800 degrees C. Furthermore, proton conducting reversible solid oxide cells (PC-RSOCs) with LSN and PSN air electrodes exhibit maximum power densities of 046 and 035 W cm(-2) in solid oxide fuel cell mode at 700 degrees 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 degrees 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 Ln(1.2)Sr(0.8)NiO(4) could be suitable candidates of air electrodes in intermediate-temperature PC-RSOCs. (C) 2018 Elsevier Ltd. All rights reserved.