Materials Development for Fuel Cells
Cathode Matierals, Electrolyte Materials, Hydrogen Membranes

Current Projects

Project Title: Effect of Co-doping on the Electrical Properties of Ceria Electrolyte
Funding Agency: NASA
Contract Number: NAG 2930

Solid oxide fuel cell (SOFC) technology promises high efficiency in generating electricity from hydrocarbons. SOFCs based on an yttria stabilized zirconia electrolyte operate at temperature (~1000^oC) to avoid unacceptably high ohmic losses. These high operating temperature conditions place considerable constraint on the materials that can be used for interconnects and balance of plant. In recent years, doped ceria electrolytes have opened up the possibility for such intermediate temperatures SOFCs due to their higher ionic conductivity and good thermodynamic stability. Among doped ceria electrolytes, Gd_0.10Ce_0.90O2_-d (GDC) is widely accepted as having the highest ionic conductivity. In search of advanced materials, we have investigated co-doping ceria with the main focus of designing an electrolyte that exhibits higher ionic conductivity than that of GDC. In our recent work, we developed co-doped ceria electrolyte that exhibit 30% higher ionic conductivity than GDC at 550^oC.

Papers
• “Higher conductivity Sm3+ and Nd3+ co-doped ceria based electrolyte materials", Shobit Omar, Eric D. Wachsman, and Juan C. Nino, Solid State Ionic, accepted 178 [37-38] 1890-1897 (2008).
• “Higher ionic conductive ceria based electrolytes for solid oxide fuel cells", Shobit Omar, Eric D. Wachsman, and Juan C. Nino, Applied Physics Letters, 91 [14] Art. No. 144106 (2007).
• “A co-doping approach towards enhanced ionic conductivity in fluorite-based electrolytes”, Shobit Omar, Eric D. Wachsman, and Juan C. Nino, Solid State Ionics, 177 [35-36] 3199-3202 (2006).

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Project Title: Pyrophosphate SnP₂O₇ for Proton Conduction Membrane
Funding Agency: NSF
Contract Number:

Proton exchange membrane fuel cells (PEMFC) have the advantages of high energy efficiency and low pollutant emissions. The key part of the PEMFC is the electrolyte which requires high proton conductivity and good thermal stability at working ambient. So far materials with both the properties are yet to be developed. Recent research showed Indium doped SnP₂O₇ exhibited good potential as proton conducting material operating at intermediate temperatures. However, the dopant behavior and proton incorporation mechanism in this material are not well explained. Furthermore, previous research was conducted based on the unsintered porous SnP₂O₇ pellet, which limited its application as proton conducting membrane. It is therefore the interest of this proposed work to investigate the proton conductivity of this material by making dense samples. The acceptor doped SnP₂O₇ will be synthesized through conventional solid state processing method. The crystal structure and phase purity of the compound will be examined by X-ray diffraction (XRD). Electrochemical impedance spectroscopy (EIS) will be utilized to measure the total conductivity. Proton transport number will be measured by measuring the electromotive force (EMF) under hydrogen gas environment. The microstructure of acceptor doped SnP₂O₇ will be examined by scanning electron microscopy (SEM). The results will be combined with conductivity measurements to optimize the composition and processing parameters of acceptor doped SnP₂O₇. As the ultimate objective of this proposed work, a fuel cell with acceptor doped SnP₂O₇ as electrolyte will be assembled and the performance will be evaluated. This study will give us better understanding on the proton conduction mechanism of acceptor doped SnP₂O₇ and provide us information to evaluate this material as proton conducting electrolyte.