Evaluation of Nickel for Use as an Interconnect in Solid Oxide Fuel Cells
Solid oxide fuel cells are devices that have the potential to efficiently produce electricity while creating little pollution. The development of a suitable interconnect is one of the primary technological hurdles that is holding back their commercial viability. An interconnect has two primary functions in a planar solid oxide fuel cell stack. First, the interconnect must separate the anode gas of one cell from the cathode gas of the adjacent cell and second, the interconnect must provide an electrical connection between adjoining cells. During operation, the ability of the interconnect to perform both of these functions can be compromised.
An interconnect is simultaneously exposed to an anode gas of hydrogen, or hydrogen- hydrocarbon mixtures, and a cathode gas of air. Degradation can occur as a result of this dual atmospheric exposure because both hydrogen and oxygen can dissolve in high concentrations making the interconnect susceptible to a phenomenon known as chemically driven cavity growth (CDCG) which can compromise the mechanical properties of the interconnect. Nickel, silver and nickel-silver composites were studied under dual atmospheric conditions for times up to 600 hours in order to study their mechanical stability. The microstructural evolution was studied using SEM, and a model was developed to predict under what conditions CDCG would occur and what the rate of degradation would be.
The electrical properties of pure nickel, a Ni-5wt%Cu alloy, and both Ni, and Ni-5Cu coated with CeO2 were measured using a direct current four-point probe. These tests, in conjunction with thermogravimetric analysis, were used to determine the rate of degradation with time. The best electrical properties were observed in the CeO2 coated nickel system.
In addition, a simple theoretical model which describes the electrical degradation of nickel as a function of time was developed and showed good agreement with the experimental results. This model could be used to estimate how the electrical properties of new candidate interconnect materials will degrade during fuel cell operation.
Advisor:N.G. Eror; F.S.Pettit; J.P. Leonard; G.H. Meier
School:University of Pittsburgh
School Location:USA - Pennsylvania
Source Type:Master's Thesis
Keywords:materials science and engineering
Date of Publication:09/25/2007