2017 Volume 125 Issue 4 Pages 202-207
Various compositions of mixture of silver (Ag) and nickel oxide (NiO) powders are studied for use as a cathode contact material in solid oxide fuel cell stacks. The addition of NiO is intended to mitigate Ag evaporation and maintain low resistivity of the contact material during stack operation. It is found that the mixture in the form of pellets consisting of 20 mol % Ag and 80 mol % NiO can yield acceptable area specific resistance (ASR) 2.24 mΩ cm2 at 800°C with reduced weight loss. However, in the steel/Ag–NiO paste/steel assemblies prepared with 30–50 mol % Ag in mixed powders, each paste containing 64 wt % mixed powder, high ASR values of ∼100–200 mΩ cm2 after 1552 h thermal exposure at 800°C are observed. The low resistivity of the pellet with 20 mol % Ag is attributed to the formation of effective conducting pathways by complete sintering of the densely packed Ag particles through the pressing process in producing the pellets. For the steel/Ag–NiO paste/steel assemblies, Ag particles are scattered within the Ag–NiO layer and cannot readily get sintered. It is found that the resistance of Ag–NiO mixture critically depends on the mass concentration of Ag powder.