Fuel cells and fuel cell plates

Details Fuel cells and fuel cell plates Fuel cells and fuel cell plates

2001-03-14

2004-09-14

Kalafut, Stephen J. (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S006000, C429S006000, C428S472000

Reexamination Certificate

active

06790554

ABSTRACT:

The present invention relates to plates for fuel cells, to fuel cells comprising such plates and particularly to so-called proton-exchange membrane fuel cells.
A fuel cell is an electrochemical device in which electricity is produced without combustion of fossil fuel.
In a fuel cell a fuel, which is typically hydrogen, is oxidised at a fuel electrode (anode) and oxygen, typically from air, is reduced at a cathode to produce an electric current and form by-product water. An electrolyte is required which is in contact with both electrodes and which may be alkaline or acidic, liquid or solid. Heat and water are the only by-products of the electrochemical reaction in fuel cells wherein the fuel is hydrogen. Accordingly, the use of such cells in power generation offers potential environmental benefits compared with power generation from combustion of fossil fuels or by nuclear activity.
In proton-exchange membrane fuel cells, hereinafter referred to for convenience as “PEM” fuel cells, the electrolyte is a solid polymer membrane which allows transport of protons from the anode to the cathode and is typically based on perfluorosulphonic acid materials. The electrolyte must be maintained in a hydrated form during operation in order to prevent loss of ionic conduction through the electrolyte.
A PEM fuel cell typically comprises two electrodes, an anode and a cathode, separated by a proton-exchange membrane electrolyte. At the anode, hydrogen fuel catalytically dissociates into free electrons and protons. The free electrons are conducted in the form of usable electric current through the external circuit with which the fuel cell is in electrical contact. The protons migrate through the membrane electrolyte to the cathode where they combine with oxygen from the air and electrons from the external circuit to form water and generate heat. Individual fuel cells may be combined into assemblies which are often referred to in the art as stacks to provide the amount of power required.
A PEM fuel cell assembly comprises a plurality of such individual cells. In a fuel cell assembly bipolar or separator plates, also known as fluid flow field plates, play a significant role. The bipolar or separator plate is fabricated with surface features, for example a series of corrugations or a serpentine pattern, which provide gas flow channels which ensure essentially even distribution of input gases over the electrode surfaces. The bipolar or separator plate should have high electrical conductivity as an ohmic loss in the plate will reduce the overall assembly efficiency.
Bipolar plates for fuel cells constructed from metals, referred to therein as bipolar terminal grids, have been described by Douglas et al in U.S. Pat. No. 3,134,696. Bipolar plates for fuel cells constructed from carbon/polymer composites, referred to therein as bipolar current collectors-separators, have been described by Lawrence in U.S. Pat. No. 4,214,969. Bipolar plates for fuel cells constructed from graphite, referred to therein as fluid flow field plates, have been described by Wilkinson et al in WO 95/16287. The disclosures in these patent specifications are incorporated herein by way of reference.
Fuel cells may include other forms of plates such as current collecting plates by means of which electrical current generated by the chemical reaction is collected for delivery to an external circuit.
We have now found that the electrical conductivity of plates for fuel cells can be increased by coating them with a coating of an electrocatalytically-active material.
In broad terms, the present invention is concerned with a plate, for use in a fuel cell assembly, for (a) conducting current and/or (b) distributing fluid, the plate comprising a substrate with a coating of an electrocatalytically-active material, preferably comprising ruthenium oxide.
By “electrocatalytically-active material” we mean a material which where used as an electrode or coating therefor catalyses electrochemical reactions at high current densities at potentials close to the equilibrium potential as is more fully described by R Greef et al in “Instrumental Methods in Electrochemistry”, Ellis Horwood, 1990 and by D Pletcher et al in “Industrial Electrochemistry”, Chapman and Hall, 1990.
The plate may comprise a bipolar or separator plate or it may comprise a current-collecting plate of the fuel cell.
The plate according to the present invention may be provided with surface features, for example an in-plane non-uniform structure, which may be regular or irregular, e.g. a series of corrugations or serpentine pattern, which provide gas flow channels which ensure essentially even distribution of fuel, e.g. input gases, over the electrode surfaces and facilitate transport of by-products, e.g. water, therefrom.
Such surface features may be formed by techniques well known to those skilled in the art, for example embossing or die-casting.
According to another aspect of the present invention there is provided a fuel cell comprising
a) at least two bipolar or separator plates;
b) a membrane electrode assembly disposed between the plates, which membrane electrode assembly comprises a pair of opposed electrodes with a proton-exchange membrane disposed therebetween with the proviso that where the fuel cell comprises more than two plates a membrane electrode assembly and a plate alternate throughout the cell and the membrane electrode assemblies are disposed in the fuel cell such that an anode and a cathode alternate throughout the cell;
c) current-collecting means;
d) means to feed gaseous hydrogen fuel to the anodes; and
e) means to feed an oxygen-containing gas to the cathode;
characterised in that each bipolar or separator plate comprises a plate according to the first aspect of the present invention.
According to a third aspect of the present invention there is provided a fuel cell assembly comprising:
a) a plurality of cell units each of which contains a proton-exchange membrane separating the cell into anolyte and catholyte chambers and provided with an anode and a cathode on opposite sides thereof;
b) a bipolar or separator plate disposed between adjacent cell units;
c) current-collecting means;
d) means to feed hydrogen fuel to the anolyte chambers of the cell; and
e) means to feed an oxygen-containing gas to the catholyte chambers of the cell;
characterised in that each bipolar or separator plate comprises a plate according to the first aspect of the present invention.
The current-collecting means serve to provide a connection to an external circuit and are preferably terminal current-collector plates. The current collecting means may likewise comprise a plate according to the first aspect of the invention.
According to another aspect of the present invention there is provided a fuel cell stack comprising a plurality of individual fuel cell units located between a pair of current-collecting plates with bipolar or separator plates provided between adjacent fuel cell units, characterised in that at least one of said plates includes a substrate with a coating of an electrocatalytically-active material as herein defined, preferably comprising ruthenium oxide.
According to a further aspect of the present invention there is provided a fuel cell stack comprising a plurality of individual fuel cell units and end plates and/or current-collecting plates of the stack associated with the stack, characterised in that at least one of said plates includes a substrate with a coating of an electrocatalytically-active material as herein defined.
The end and/or current-collecting plates of the fuel cell stack may be provided with means for collecting current generated during operation of the stack, means for controlling fluid distribution within the interior of the stack, means for use in applying clamping forces to the stack and means for the supply and removal of fluids from the stack.
The substrate may be provided with fluid flow channels. For example, the end and/or current collecting plate(s) provided with such coating may be of a monolithic or unitary construction incorporating fl

Affiliated with

Also associated with

Rating

Fuel cells and fuel cell plates does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Fuel cells and fuel cell plates, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fuel cells and fuel cell plates will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3267499