FUEL CELL FLOW FIELD HAVING METAL BIPOLAR PLATES
A bipolar plate ( 30, 30 ′) for use in a fuel cell ( 12, 14 ) includes a first metal layer ( 40 a ) having a first corrosion potential and a second metal layer ( 40 b ) that tends to grow an oxide layer ( 42, 42 ′) during operation of the fuel cell ( 12, 14 ). The second metal layer ( 40 b ) includes a second corrosion potential such that there is a corrosion potential gradient between the first metal layer ( 40 a ) and the second metal layer ( 40 b ) that resists growth of the oxide layer ( 42, 42 ′).
1 . An article for use in a fuel cell, comprising:
a bipolar plate having a first metal layer having a first corrosion potential; and
a second metal layer galvanically coupled with the first metal layer and having an oxide layer during operation of the fuel cell, the second metal layer having a second, different corrosion potential such that there is a corrosion potential gradient between the first metal layer and the second metal layer that is operative to control growth of the oxide layer at the second metal layer.
2 . The article as recited in claim 1 , wherein the second corrosion potential is between about 200 mV different relative to the first corrosion potential.
3 . The article as recited in claim 2 , wherein the second corrosion potential is between about 30 mV and about 50 mV different relative to the first corrosion potential.
4 . The article as recited in claim 1 , wherein the oxide layer has an associated growth rate, and wherein the corrosion potential gradient reduces the growth rate.
5 . The article as recited in claim 1 , wherein the first metal layer includes a stainless steel and the second metal layer includes at least one of a nickel-based alloy or a nickel-chromium based alloy.
6 . The article as recited in claim 5 , wherein:
the first metal layer includes a nominal composition of between about 50 wt % to 70 wt % of Fe, about 9 wt % to 26 wt % of Ni, about 12 wt % to 25 wt % of Cr, about 2 wt % to 4 wt % of Mo, and about 1 wt % to 2 wt % of Mn; and
the second metal layer includes a nominal composition of about 55 wt % to 75 wt % Ni, about 15 wt % to 23 wt % Cr, about 2 wt % to 25% of Mo, about 10 wt % to 14 wt % W, about 2 wt % to 5 wt % of Fe, and about 0.5 wt % to 1 wt % of Mn.
7 . The article as recited in claim 6 , including a third metal layer having a nominal composition equal to the nominal composition of the second metal layer, wherein the first metal layer is between the second metal layer and the third metal layer.
8 . The article as recited in claim 1 , wherein the first metal layer includes a solid, continuous planar section and the second metal layer includes a non-continuous section directly adjacent the solid, continuous planar section.
9 . The article as recited in claim 1 , wherein the non-continuous section comprises a mesh.
10 . The article as recited in claim 6 , wherein the amount of Fe is about 60 wt % to 65 wt %, the amount of Ni is about 10 wt % to 14 wt %, and the amount of Cr is about 16 wt % to 18 wt % in the nominal composition of the first metal layer.
11 . The article as recited in claim 1 , wherein corrosion potential gradient is operative to prevent a thickness of the oxide layer from exceeding a threshold.
12 . The article as recited in claim 1 , wherein the corrosion potential gradient is operative to reduce a thickness of the oxide layer.
13 . The article as recited in claim 1 , wherein the corrosion potential gradient is operative to prevent an electrical contact resistance from exceeding a threshold.
14 . A method for use with a fuel cell, comprising:
(a) forming a bipolar plate using a metal layer having a potential to grow an oxide layer; and
(b) establishing a corrosion potential gradient for controlling a nominal growth rate of the oxide layer growing at the metal layer.
15 . The method as recited in claim 14 , including galvanically coupling another metal layer of the bipolar plate to the metal layer of the bipolar plate.
16 . The method as recited in claim 15 , including controlling the nominal growth rate to maintain a selected conductivity of the oxide layer.
17 . The method as recited in claim 16 , including galvanically dissolving the metal within the oxide layer to reduce the growth rate.
18 . The method as recited in claim 15 , including controlling a rate of galvanic dissolution by selecting a desired ratio of exposed surface area between the metal layer and the another metal layer.
19 . The method as recited in claim 14 , including permitting growth of the oxide layer while operating the fuel cell to generate an electric current, and galvanically dissolving the oxide layer when the fuel cell is not operating to generate an electric current.
20 . A fuel cell assembly comprising:
a cell stack having a plurality of electrodes; and
a plurality of bipolar plates associated with corresponding electrodes, each of the bipolar plates comprising:
a first metal layer having a first corrosion potential; and
a second metal layer galvanically coupled with the first metal layer and having a potential to grow an oxide layer during operation of the fuel cell, the second metal layer having a second, different corrosion potential such that there is a corrosion potential gradient between the first metal layer and the second metal layer that is operative to control growth of the oxide layer at the second metal layer.
21 . The assembly as recited in claim 20 , wherein the first metal layer and the second metal layer are in direct contact.