Electrochemical activity of perovskite-like LaNiO3 as SOEC anode

La2NiO4+δ and its derivatives with perovskite-related K2NiF4-type structure demonstrate high mixed ionic-electronic conductivity, moderate thermal and negligible chemical expansion. As a result, these phases attracted... [ view full abstract ]

La₂NiO_4+δ and its derivatives with perovskite-related K₂NiF₄-type structure demonstrate high mixed ionic-electronic conductivity, moderate thermal and negligible chemical expansion. As a result, these phases attracted significant attention as cathode materials for intermediate-temperature SOFCs. At the same time, perovskite-like LaNiO_3-δ have not been considered for these applications, mostly due to the limited phase stability under ambient oxygen pressures. On heating in air, it decomposes at ~1000 °C; cathodic polarization can be expected to induce the decomposition of perovskite phase at lower temperatures characteristic for IT-SOFC operation. On the contrary, redox changes imposed by anodic polarization under oxidizing conditions should not be of risk for the LaNiO_3-δ phase stability. The present work aimed at the characterization of LaNiO_3-δ as oxygen electrode of solid oxide electrolysis cells.

Single-phase LaNiO_3-δ powder with rhombohedrally-distorted perovskite-like structure was prepared by glycine-nitrate combustion synthesis followed by calcinations in oxygen atmosphere at 800-1000 °C. Porous ceramic samples with relative density of 55-58% for electrical and dilatometric studies were sintered in oxygen at 1050 °C. Porous LaNiO_3-δ samples demonstrated p-type metallic-like electrical conductivity, 400-500 S/cm at 800-600°C, and moderate thermal expansion (average CTE ~13.0 ppm/K at 25-800°C) ensuring compatibility with solid electrolytes.

LaNiO_3-δ electrode layers were applied on different solid electrolytes, including (ZrO₂)_0.92(Y₂O₃)_0.08 (8YSZ), Ce_0.9Gd_0.1O_2-δ (CGO10), and (La_0.8Sr_0.2)_0.98Ga_0.8Mg_0.2O_3-δ (LSGM), and sintered at 1050 °C for 2h in O₂. The studies of symmetrical cells demonstrated that electrochemical activity of LaNiO_3-δ electrodes increases in the sequence 8YSZ3-δ electrodes on LSGM electrolyte can be further reduced down to 0.03 Ohmxcm at 800°C and 0.11 Ohmxcm at 700 °C by surface modification with praseodymia. The performance of LaNiO_3-δ electrodes under steady-state anodic polarization was evaluated using 3-electrode configuration at 600-800°C.