Long‐term oxidation and electrical behavior of Nb‐doped Ti3SiC2 as solid oxide fuel cell interconnects

Nb-doped Ti3SiC2 compounds ((Ti1-xNbx)3SiC2, x=0%, 2%, 5%, 7%, and 10%) as novel interconnect materials of intermediate temperature solid oxide fuel cell (IT-SOFC) were studied in the simulated cathode atmosphere. The long-term oxidation behaviors and area-specific resistance (ASR) of these compounds have been investigated at 800°C up to 700 hours. Among these compounds, (Ti0.95Nb0.05)3SiC2 shows the best oxidation resistance and lowest postoxidation ASR (5.6 mΩ·cm2 after exposure at 800°C in air for 700 hours), endowing it a great promising material in the application as interconnect of IT-SOFC. After oxidation, Nb is mainly doped uniformly into the lattice of rutile-TiO2 (r-TiO2) grains formed on the tested compounds. Nb doping could decrease the concentrations of both oxygen vacancies and titanium interstitials in r-TiO2. As a result, the oxidation rate of (Ti,Nb)3SiC2 decreases remarkably, the structure of the oxide scale changes from a duplex layer of TiO2 outer layer and TiO2+SiO2 mixture inner layer to a single mixture layer. Nb doping also increases the amount of semifree electrons, causing the significant reduce of the postoxidation ASR of (Ti,Nb)3SiC2.