Nd-Nickelate Solid Oxide Fuel Cell Cathode Sensitivity to Cr and Si Contamination

摘要

The stability of Nd-nickelate, considered as an alternative solid oxide fuel cell (SOFC) cathode material, was evaluated in this work on its tolerance towards contaminants. Symmetrical cells with Nd1.95NiO~(4+) (NNO) electrodes on gadolinia-doped ceria electrolyte supports were monitored over time-spans of 1000 h under polarization in an air-flux with deliberate chromium contamination. Impedance spectroscopy pointed out a polarization increase with time by the growth of the low frequency arc describing the electrode's oxygen reduction and incorporation processes. Post-test observations revealed polluted cathode regions with increasing amounts of Cr accumulations towards the electrolyte/cathode interface. Cr deposits were evidenced to fully cover active nickelate grain surfaces forming Nd-containing Cr oxides. In addition to exogenous Cr contamination, endogenous contamination was revealed. Silicon, present as impurity material in the raw NNO powder (introduced by milling during powder processing), reacts during sintering steps to form Nd-silicate phases, which decreases the active cathode surface. Nd-depletion of the nickelate, as a result of secondary phase formation with the contaminants Cr and Si (NdCrO4 and Nd4Si3O_(12)), then triggers the thermally induced decomposition of NNO into stoichiometric Nd2NiO~(4+) and NiO. Summarized, the alternative Nd-nickelate cathode also suffers from degradation caused by pollutant species, like standard perovskites.