Electrochemical properties of Ni-YSZ cermet in solid oxide fuel cells - Effect of current collecting

The effects of various current collectors on the electrochemical property m easurements of a Ni-YSZ cermet have been investigated. Electrochemical char acteristics were determined by impedance spectroscopy (LS) at open-circuit voltage in H-2-H2O atmosphere at 800 degrees C using a symmetrical cell. We selected various current collectors made of gold, platinum and nickel and with two different structures, paste and mesh. When using paste, the electr ochemical response, recorded with the same Ni-YSZ cermet sample, depends gr eatly on the nature of the current collector. Polarization resistance value s follow the order: Ni < Pt < Au. This is the same order as reported in the literature for the hydrogen electrochemical oxidation activities of these metals. This demonstrates that paste current collectors interfere with the electrochemical properties of the anode material. Therefore, in order to co mpare the electrochemical activities of various anode materials, the same c urrent collector has to be used. We have also observed that the polarizatio n resistance increases with time, due to metal particle diffusion through t he Ni-YSZ cermet. When using a nickel mesh, the electrochemical properties do not vary with time. Moreover, the structure of this current collector is most similar to the interconnect materials, which are the current collecto rs in planar SOFCs. It is, therefore, the best current collector for the st udy of the electrochemical properties of Ni-YSZ cermet. (C) 2000 Elsevier S cience BN. All rights reserved.