Semester

Summer

Date of Graduation

2012

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Edward M Sabolsky

Abstract

Solid Oxide Fuel Cells (SOFC's) have the potential for producing highly efficient energy through conversion of chemical energy to electrical energy at high temperatures (>600°C). Until recently, pure hydrogen fuel (H2) is the prime fuel used within these devices. However, the high processing costs associated with clean hydrogen production combined with the abundance of available fossil fuels within the United States has opened the door for research on alternative fuels to power these cells. Among the biggest obstacles associated with this concept are the contaminants that are present in raw fuels such as natural gas or coal. While gas-cleanup technology is continually improving, parts per million (ppm) concentrations of species such as hydrogen sulfide (H2S) and phosphine (PH3) prove to be harmful to the traditional nickel-yttrium stabilized zirconia (Ni/YSZ) anode due primarily to the interactions with the Ni catalyst. In this work, a nickel-gadolinium doped ceria (Ni/GDC) anode is processed with a GDC barrier layer between the anode and electrolyte for evaluation in H2S-laden H2 and coal derived synthesized gas (syngas). Additionally, a novel Sr2MgMoO6-delta/GDC anode (both electrolyte supported and anode supported) is developed for testing in fuels containing both H2S and PH3. The central findings of this work are that the Ni/GDC anode with a GDC barrier layer can remain stable in syngas fuel with 100 ppm H2S. The same cell showed relatively high stability in wet H2 fuel with up to 1000 ppm H2S without significant degradation and the barrier layer was shown to be essential to this stability. Specifically, the barrier layer helps to prevent nickel oxidation near the anode-electrolyte interface and to electrochemically oxidize the sulfur for additional power production. Also, the Sr2MgMoO 6-delta/GDC composite anode showed much improved tolerance to 10 ppm PH3 than the traditional Ni/YSZ cermet anode with the major cause of degradation being localized de-lamination at the anode/electrolyte interface and densification and de-lamination of the Pt contact from the anode. Unlike the Ni/YSZ anode, the SMM anode constituents were not found to be chemically reactive with P for our operating conditions.

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