Microstructural and Electrochemical Study of Charge Transport and Reaction Mechanisms in Ni/YSZ Anode

The microstructure and chemical changes in the Ni-YSZ heterojunctions were studied by scanning, transmission and high-resolution electron microscopy and X-ray diffraction. It was shown that new nano-size Ni grains are formed at Ni-YSZ interface at the cell operation. The following two stage reaction mechanism was proposed for hydrogen oxidation on the nano-size Ni grains: 1. NiO + Н2 ⇒ Н2О + Ni; 2. O2⎯(YSZ) + Ni ⇒ NiO + 2e. This mechanism implies that the SOFC will operate during some time even after switching off the hydrogen flow. We have observed and investigated current-voltage characteristics of SOFC after cutting off the hydrogen pass through anode chamber. Electrochemical properties of SOFC were investigated as a function of Ni volume content for two different geometry of anode current collector. Good correlations of experimentally measured SOFC characteristics with results of numeric calculations were found