Synthesis and evaluation of double-layer electrodes using a Ni–BaCe0.50Zr0.27Y0.20Ni0.03O3−δ cermet with a fused-aggregate network structure as the hydrogen electrode of solid oxide cells

We have evaluated double-layer hydrogen electrodes with catalyst layers (CLs) and current-collecting layers (CCLs) in order to apply them in proton-conducting solid oxide cells. The scaffolds of the CLs were fabricated from a composite of mixed protonically-electronically conductive (MPEC) perovskite oxide BaCe0.50Zr0.27Y0.20Ni0.03O3−δ (BCZYN) and Ni on a BaCe0.10Zr0.70Y0.20O3−δ electrolyte. Both powders were synthesized via a flame oxide-synthesis method and both had a unique microstructure, i.e., a fused-aggregate network structure [BCZYN(fans), Ni(fans)]. This unique structure was constructed from both a network of particles fused with their nearest neighbors and pores surrounded by the fused particles. This structure was found to be favorable for constructing both electronically conductive pathways and gas diffusion pathways in the CLs. Highly dispersed Ni nanoparticles [Ni(np)] were also loaded on the MPEC of BCZYN(fans) in the CLs. Composite CCLs of micrometer-sized BaCe0.50Zr0.30Y0.20O3−δ and Ni were also fabricated on the CLs. The catalytic activity of a hydrogen electrode using a CL comprising a composite of BCZYN(fans) and Ni(fans) was higher than that of a CL comprising BCZYN(fans) at a Ni(np) loading amount of 30 vol.% due to the improvement of the electronic conductivity in CLs by Ni(fans). The catalytic activity of the hydrogen electrode using the CLs increased with increases in the Ni(np) loading amount, moreover, and reached saturation at around 30 vol.% due to relief from the effect of the depletion layer on the outer surface of BCZYN(fans).