Cathode materials for La0.995Ca0.005NbO4 proton ceramic electrolyte

The study presents the chemical and mechanical compatibility of the proton conducting electrolyte La0.995Ca0.005NbO4 (LCNO) with the LSM, LSCM and BSCF cathodes and the electrochemical performance of symmetrical cells based on LCNO. After annealing at high temperature the electrolyte-cathode mixtures in air and wet air, the obtained products were analyzed by X-ray powder diffraction (XRPD). The microstructure of the cathode and electrolyte materials and the interfaces were observed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX). The results show that LSCM cathode is chemically and mechanically stable with the LCNO electrolyte although the BSCF cathode reacts with it. Cation diffusion was observed between LSM cathode and LCNO electrolyte after the heat treatment of their mixture at T = 1150 °C. The electrochemical study performed on symmetrical cells revealed that the LSCM cathode presents the lowest value of area specific resistance (ASR) compared to the ones of the LSM and BSCF cathodes: ASRLSCM = 35 Ω cm2; ASRLSM = 57 Ω cm2; ASRBSCF = 416 Ω cm2 (in humidified air at 750 °C). Finally, a CER–CER approach was used in order to minimize the polarisation resistance of the LSM cathode by mixing LSM and LCNO in different volumetric ratios. The lowest value of ASR for LSM-based composite cathode was obtained by adding 50 vol.% of LCNO to LSM cathode (ASRLSM/LCNO = 22 Ω cm2 in humidified air at 750 °C).