Long‐term oxidation and electrical behavior of Nb‐doped Ti ₃ SiC ₂ as solid oxide fuel cell interconnects

Abstract

Abstract Nb‐doped Ti 3 SiC 2 compounds ((Ti 1‐ x N b x ) 3 SiC 2 , 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, (Ti 0.95 Nb 0.05 ) 3 SiC 2 shows the best oxidation resistance and lowest postoxidation ASR (5.6 mΩ·cm 2 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‐TiO 2 (r‐TiO 2 ) grains formed on the tested compounds. Nb doping could decrease the concentrations of both oxygen vacancies and titanium interstitials in r‐TiO 2 . As a result, the oxidation rate of (Ti,Nb) 3 SiC 2 decreases remarkably, the structure of the oxide scale changes from a duplex layer of TiO 2 outer layer and TiO 2 +SiO 2 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) 3 SiC 2 .