Summary The development of a cobalt-free cathode with long-term stability and high electrochemical activity is important for constructing low-cost and robust solid oxide fuel cells (SOFCs). Here, we report performance enhancement of a cobalt-free cathode achieved by valence regulation of the ferrite-based perovskite. Utilizing co-doping of high valence niobium with low valence nickel, we developed a cathode material La 0.8 Sr 0.2 Fe 0.8 Ni 0.15 Nb 0.05 O 3−δ that allowed representing adequate conductivity of 214 S cm −1 at 700°C, decent thermal compatibility with thermal expansion coefficient being 12 × 10 −6 K −1 , superior electrochemical properties manifested by area-specific resistance of 0.06 Ω cm 2 and peak power density of 760 mW cm −2 at 800°C, and excellent discharge durability of over 480 h at a current density of 460 mA cm −2 under 750°C. This significantly enhanced performance originates from a proper regulation of the electronic structure rendered by synergistic effects induced by the co-doping of the high valence niobium with low valence nickel into the B sites of the ferrite perovskite. Such a regulation enables an optimized compromise among the oxygen vacancies, electronic mobility, oxygen adsorption and dissociation, and strontium segregation.
Chengsheng Ni,Qimiao Zeng,Debo He,Luo Peng,Deti Xie,John T. S. Irvine,Shukai Duan,Jiupai Ni
Compared to a Ni(O) cermet, an oxide anode is much better for a solid oxide fuel cell at suppressing coking and carbon deposition from carbonaceous fuels. Furthermore, a small amount of metal nanoparticles can enhance the electrochemical performance of the oxide anode while maintaining compatibility with the carbonaceous fuel when anchored on the oxide surface. In this study, ferrate-based perovskites (La0.95Fe0.80Ni0.05Ti0.15O3, LFNT) with Ni0 particle exsolution are investigated via B-site doping to increase the stability at 800 °C in a H2 atmosphere and electrocatalytic capability for fuel oxidation. Surprisingly, the B-site doped LaFeO3 (La0.95Fe0.8Mg0.2O3, LFM) showed a high oxide-ion conductivity of 3.8 mS cm−1 with limited electronic conduction and further doping of Ti4+ or Ni2+ could increase the electronic conductivity to 30 S cm−1 and 100 S cm−1 at 800 °C for the reduced La0.95Fe0.8Mg0.05TiO3 (LFMT) and LFNT, respectively. The cell with the LFNT anode on a La0.9Sr0.1Ga0.8Mg0.2O2.85 electrolyte shows a polarisation resistance of 0.32 Ω cm2 at 800 °C, and a high power density of 600 mW cm−2 can be obtained when ceria is added via infiltration as a co-catalyst.
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