Fluid distribution surface for solid oxide fuel cells

Details Fluid distribution surface for solid oxide fuel cells Fluid distribution surface for solid oxide fuel cells

2001-06-27

2004-08-10

Maples, John S. (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S006000, C429S006000

Reexamination Certificate

active

06773845

ABSTRACT:

BACKGROUND
Alternative transportation fuels have been represented as enablers to reduce toxic emissions in comparison to those generated by conventional fuels. At the same time, tighter emission standards and significant innovation in catalyst formulations and engine controls have led to dramatic improvements in the low emission performance and robustness of gasoline and diesel engine systems. This has certainly reduced the environmental differential between optimized conventional and alternative fuel vehicle systems. However, many technical challenges remain to make the conventionally fueled internal combustion engine a nearly zero emission system having the efficiency necessary to make the vehicle commercially viable.
Alternative fuels cover a wide spectrum of potential environmental benefits, ranging from incremental toxic and carbon dioxide (CO
2
) emission improvements (reformulated gasoline, alcohols, liquid petroleum gas, etc.) to significant toxic and CO
2
emission improvements (natural gas, dimethylether, etc.). Hydrogen is clearly the ultimate environmental fuel, with potential as a nearly emission free internal combustion engine fuel (including CO
2
if it comes from a non-fossil source). Unfortunately; the market-based economics of alternative fuels, or new power train systems, are uncertain in the short to mid-term.
The automotive industry has made very significant progress in reducing automotive emissions in both the mandated test procedures and the “real world”. This has resulted in some added cost and complexity of engine management systems, yet those costs are offset by other advantages of computer controls: increased power density, fuel efficiency, drivability, reliability and real-time diagnostics.
Future initiatives to require zero emission vehicles appear to be taking us into a new regulatory paradigm where asymptotically smaller environmental benefits come at a very large incremental cost. Yet, even an “ultra low emission” certified vehicle can emit high emissions in limited extreme ambient and operating conditions or with failed or degraded components.
One approach to addressing the issue of emissions is the employment of fuel cells, particularly solid oxide fuel cells (“SOFC”), in an automobile. A fuel cell is an energy conversion device that generates electricity and heat by electrochemically combining a gaseous fuel, such as hydrogen, carbon monoxide, or a hydrocarbon, and an oxidant, such as air or oxygen, across an ion-conducting electrolyte. The fuel cell converts chemical energy into electrical energy. A fuel cell generally consists of two electrodes positioned on opposites of an electrolyte. The oxidant passes over the oxygen electrode (cathode) while the fuel passes over the fuel electrode (anode), generating electricity, water, and heat.
SOFC's are constructed entirely of solid-state materials, utilizing an ion conductive oxide ceramic as the electrolyte. A conventional electrochemical cell in a SOFC is comprised of an anode and a cathode with an electrolyte disposed therebetween. In a typical SOFC, a fuel flows to the anode where it is oxidized by oxygen ions from the electrolyte, producing electrons that are released to the external circuit, and mostly water and carbon dioxide are removed in the fuel flow stream. At the cathode, the oxidant accepts electrons from the external circuit to form oxygen ions. The oxygen ions migrate across the electrolyte to the anode. The flow of electrons through the external circuit provides for consumable or storable electricity. However, each individual electrochemical cell generates a relatively small voltage. Higher voltages are attained by electrically connecting a plurality of electrochemical cells in series to form a stack.
The SOFC cell stack also includes conduits or manifolds to allow passage of the fuel and oxidant into and byproducts, as well as excess fuel and oxidant, out of the stack. Generally, in certain cell configurations, oxidant is fed to the structure from a manifold located on one side of the stack, while fuel is provided from a manifold located on an adjacent side of the stack. The fuel and oxidant are generally pumped through the manifolds. From the manifolds, the fuel and oxidant are separately introduced to fluid distribution surfaces on an appropriate structure such as an interconnect between cells or an end cap. The fluid distribution surfaces are positioned in fluid communication with the appropriate electrode, with the SOFC efficiency related, in part, to fluid distribution across the surface of the electrode. Common fluid distributor surfaces, particularly for fuel electrode fluid distribution, include porous materials such as metal felts or foam metal having suitable void volume to allow passage of fluid from one or more inlet manifolds to one or more outlet manifolds.
Typically, fuel is introduced at the edge of the interconnect reacts with the electrode. In certain systems, for example where the fuel includes hydrogen and carbon monoxide, the anode reaction generally creates electrons and water. The continuing fuel stream thus further includes water. Consequently, certain regions of the electrode are prone to diminished fuel exposure, or starved. Furthermore, in certain conventional configurations such as those employing metal felt or foam metal, less than about 25% of the hydrogen in the inlet fuel stream is consumed by the fuel electrode. This detrimentally affects uniformity of temperature distribution across the electrode. These deficiencies lead to fuel waste and oxide formation, which detrimentally affects cell performance.
SUMMARY
Disclosed herein is an electrode fluid distributor. The distributor comprises a fluid passageway having a plurality of adjacent pairs of segments each including an inlet segment in fluid communication with an inlet and an outlet segment in fluid communication with an outlet. A baffle is disposed between adjacent inlet and outlet segments. Each inlet segment is in fluid communication with adjacent inlet segments and adjacent outlet segments, and each outlet segment is in fluid communication with adjacent outlet segments.
These and other features will be apparent from the following brief description of the drawings, detailed description, and attached drawings.


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