Study of Pr and Pr and Co doped La2NiO4+δ as cathodes for La5.5WO11.25−δ based protonic conducting fuel cells

The mixed ionic-electronic conductor La2NiO4+δ was investigated as potential cathode material for protonic conducting solid oxide fuel cells (PC-SOFCs) based on La5.5WO11.25−δ electrolyte. Firstly the chemical compatibility between cathode and electrolyte phases (La2NiO4+δ and La5.5WO11.25−δ respectively) was studied. Then, the electrochemical properties of this cathode were improved by partially substituting La and/or Ni, specifically La1.5Pr0.5NiO4+δ and La1.5Pr0.5Ni0.8Co0.2O4+δ were considered. These two doped materials showed improved electrical conductivity and reduced polarization resistance, when tested as cathode in symmetrical cells. In a second step, the microstructure of La1.5Pr0.5Ni0.8Co0.2O4+δ was optimized by varying the firing temperature of the cathode. The performance of these mixed conductors is limited by medium frequencies associated processes while they show lower polarization resistances (Rp) than conventional composites based on La5.5WO11.25−δ and pure electronic conductors. La1.5Pr0.5Ni0.8Co0.2O4+δ cathode sintered at 1050 °C exhibits the best electrochemical performance on a La5.5WO11.25−δ-based PC-SOFC, achieving Rp = 0.62 Ω cm2 at 750 °C in wet air.