Investigation of compatible anode systems for LaNbO4-based electrolyte in novel proton conducting solid oxide fuel cells

In the current manufacturing process of novel LaNbO4-based proton conducting fuel cells a thin layer of the electrolyte is deposited by wet ceramic coating on NiO–LaNbO4 based anode and co-sintered at 1200–1300 °C. The chemical compatibility of NiO with acceptor doped LaNbO4 material is crucial to ensure viability of the cell, so potential effects of other phases resulting from off-stoichiometry in acceptor doped LaNbO4 should also be explored. Compatibility of NiO with Ca-doped LaNbO4 and its typical off-set compositions (La3NbO7 and LaNb3O9) are investigated in this work. It is shown that while NiO does not react with Ca-doped LaNbO4, fast reaction occurs with La3NbO7 or LaNb3O9. La3NbO7 and NiO form a mixed conducting perovskite phase LaNi2/3Nb1/3O3, while LaNb3O9 and NiO form either NiNb2O6 or Ni4Nb2O9 depending on the annealing temperature. This implies that manufacturing LaNbO4-based proton conducting fuel cells requires a strict control of the stoichiometry of the electrolyte.

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► LaNbO4 and NiO are chemically compatible, but off-stoichiometric compositions, such as La3NbO7 or LaNb3O9 are not.
► The presence of La3NbO7/LaNb3O9 influences the microstructure at the NiO–LaNbO4 interface.
► Strict control of the stoichiometry of LaNbO4 is needed to use a Ni cermet anode support for PC-SOFCs.