CO2-tolerant and cobalt-free La4Ni3-xCuxO10±δ (x = 0, 0.3, 0.5 and 0.7) cathodes for intermediate-temperature solid oxide fuel cells

Abstract

Cu is doped to La4Ni3O10±δ to improve its electrochemical performance as a potential intermediate-temperature solid oxide fuel cell (IT-SOFC) cathode material. A new higher-order Ruddlesden-Popper (R-P) phase composition La4Ni3-xCuxO10±δ, (L4N3-xCx, 0.0 ≤ x ≤ 0.7) is synthesized using an EDTA-citrate process. The L4N3-xCx cathode has a good chemical compatibility with the La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolyte. A thermodynamic stability test shows that L4N3-xCx is stable after 72 h exposure to 600, 700, and 800 °C in air. The L4N3-xCx cathode shows chemical stability against CO2, and a stable structure over 12 h in CO2 has been demonstrated. The thermal expansion coefficients (TECs) have been determined to be in the range of 14.1–14.6 × 10−6 K−1, close to that of the LSGM electrolyte. The Cu content (x) significantly affects the electrical conductivity and sinter density of L4N3-xCx. La4Ni2.7Cu0.3O10 (L4N2.7C0.3) displays the highest electrical conductivity value of which reaches about 383 to 319 S cm−1 at 600–800 °C. In addition, Cu doping improves the electrochemical performance of L4N3-xCx. The area specific resistance (ASR) of the La4Ni2.5Cu0.5O10 (L4N2.5C0.5) cathode was found to be 0.045 Ω cm2 at 800 °C, which is significantly better than that of L4N3. The peak power density of a single cell using the L4N2.5C0.5 cathode is 526 mW cm−2 at 800 °C, and a 200 h long-term test demonstrates good stability. These results indicate that La4Ni3-xCuxO10±δ cathode is a promising cathode material for IT-SOFCs.