Fuel cell coolant bubble control

Abstract

To mitigate bubble blockage in water passageways ( 78, 85 ), in or near reactant gas flow field plates ( 74, 81 ) of fuel cells ( 38 ), passageways are configured with (a) intersecting polygons, obtuse angles including triangles, trapezoids, or (b) hydrophobic surfaces ( 111 ), or (c) differing adjacent channels ( 127, 128 ), or (d) water permeable layers ( 93, 115, 116, 119 ) adjacent to water channels or hydrophobic/hydrophilic layers ( 114, 120 ).

1 . A fuel cell method comprising: 
 preventing gas bubbles from blocking coolant flowing in fuel cell coolant flow paths prone to bubble blockage of coolant flowing at or below a threshold flow rate by providing coolant passageways substantially coextensive with planforms of said fuel cells which have configurations, along substantially the entire length of said coolant passageways, allowing flow of coolant below said threshold flow rate both (a) when gas is present in said passageways and (b) when gas is not present in said passageways.    
     
     
         2 . A method according to  claim 1  wherein said step of providing comprises: 
 providing coolant passageways within said coolant flow path substantially coextensive with planforms of said fuel cells (a) within and/or (b) adjacent to reactant gas flow field plates of said fuel cells configured to allow flow of said coolant therein whether or not there is any gas in said passageways.    
     
     
         3 . A method according to  claim 1  wherein said step of providing comprises: 
 providing said coolant passageways having first portions for which gas has a propensity to migrate and flow in preference over second portions of said passageways for which gas does not have such propensity.    
     
     
         4 . A method according to  claim 1  wherein said step of providing comprises: 
 configuring said coolant passageways to provide first portions for which gas has a sufficient proclivity to segregate gas from coolant so that gas present in said passageways migrates to and flows in said first portions in preference to second portions of said passageways for which gas does not have said sufficient proclivity, thereby mitigating the blockage of said coolant passageways by gas bubbles.    
     
     
         5 . A fuel cell stack comprising: 
 a plurality of fuel cells having an electrode assembly including an electrolyte having anode and cathode catalysts disposed on respective anode and cathode sides thereof, a fuel reactant gas flow field plate having fuel reactant gas flow channels extending from a first surface thereof adjacent said anode side, and an oxidant reactant gas flow field plate having oxidant reactant gas flow channels extending from a first surface thereof adjacent said cathode side, at least one of said flow field plates being porous and hydrophilic; and    a coolant flow path configured to allow coolant flow, including at least one coolant passageway disposed in or near a second surface of at least one of said flow field plates of each fuel cell which is opposite to said first surface thereof, said coolant passageways each configured to provide a first portion for which gas has a sufficient affinity to migrate to in said first portion in preference to a second portion of said passageways.    
     
     
         6 . A fuel cell stack according to  claim 5  wherein: 
 said coolant passageways are configured to provide second portions for which gas does not have said sufficient affinity, thereby mitigating the blockage of said coolant passageways by gas bubbles.    
     
     
         7 . A fuel cell stack according to  claim 5  wherein: 
 said portions extend along substantially the entire lengths of said coolant passageways.    
     
     
         8 . A fuel cell stack according to  claim 5  wherein: 
 said first portions are first channels having a first cross section; and    said second portions are second channels, having a second cross section different than said first cross section.    
     
     
         9 . A fuel cell stack according to  claim 8  wherein: 
 said second channels are smaller than said first channels.    
     
     
         10 . A fuel cell stack according to  claim 9  wherein: 
 said second channels are interspersed with said first channels.    
     
     
         11 . A fuel cell stack according to  claim 8  wherein: 
 said first channels are rectangular and said second channels are triangular.    
     
     
         12 . A fuel cell stack according to  claim 5  wherein: 
 said second channels are of different shape than said first channels.    
     
     
         13 . A fuel cell stack according to  claim 5  wherein: 
 each of said first portions is contiguous with one of said second portions.    
     
     
         14 . A stack of fuel cells according to  claim 5  wherein: 
 each of said first portions is adjacent a wall of a corresponding passageway which has a liquiphobic surface.    
     
     
         15 . A fuel cell stack according to  claim 5  wherein: 
 each of said first portions comprises a corner between two walls of a corresponding coolant passageway which subtends more than 90°.    
     
     
         16 . A fuel cell stack according to  claim 15  wherein: 
 said coolant passageways have a triangular cross section.    
     
     
         17 . A fuel cell stack according to  claim 15  wherein: 
 said coolant passageways have a trapezoidal cross section.    
     
     
         18 . A fuel cell stack according to  claim 17  wherein: 
 said trapezoidal passageways have a longer one of two parallel sides in the same plane as said second surface.    
     
     
         19 . A fuel cell stack according to  claim 5  wherein: 
 said coolant passageways are provided by composite bipolar plates interspersed between said fuel cells.    
     
     
         20 . A fuel cell stack according to  claim 19  wherein: 
 each of said bipolar plates includes a liquiphilic layer for contact with one of said reactant gas flow field plates, and at least one additional layer providing liquiphilic and liquiphobic portions between said liquiphilic layer and another one of said reactant gas flow field plates.    
     
     
         21 . A fuel cell stack according to  claim 10  wherein: 
 said liquiphilic and liquiphobic layers are hydrophilic or hydrophobic, respectively.    
     
     
         22 . A fuel cell stack according to  claim 19  wherein: 
 each said bipolar plate comprises two liquiphilic layers with a liquiphobic layer between said two liquiphilic layers.    
     
     
         23 . A fuel cell stack according to  claim 21  wherein: 
 each said bipolar plate comprises a liquiphilic layer and a layer which has separate liquiphilic and liquiphobic portions.    
     
     
         24 . A fuel cell stack according to  claim 5  wherein: 
 said coolant passageways each include at least one first coolant channel in one of said plates and at least one second coolant channel in another of said plates adjacent to said one of said plates, said second coolant channels each aligned with a corresponding one of said first coolant channels.    
     
     
         25 . A fuel cell stack according to  claim 24  wherein: 
 said second coolant channels have cross sectional areas substantially smaller than cross sectional areas of said first coolant channels.    
     
     
         26 . A fuel cell stack according to  claim 24  wherein: 
 said second coolant channels have cross sections shaped differently than the cross sectional areas of said first coolant channels.    
     
     
         27 . A fuel cell stack according to  claim 5  wherein: 
 each of said passageways has a cross section comprised of at least two each of said areas intersecting closed plane areas bounded by lines, having a cross section different from each other area.    
     
     
         28 . A fuel cell stack according to  claim 27  wherein: 
 one of said closed plane areas bounded by lines extends from said second surface of one of said plates and another of said closed plane areas bounded by lines extends from a second surface of another of said plates adjacent to said one plate.    
     
     
         29 . A fuel cell stack according to  claim 27  wherein: 
 both of said closed plane areas bounded by lines extend from said second surface of one of said plates.    
     
     
         30 . A fuel cell stack according to  claim 27  wherein: 
 said closed plane areas bounded by lines are intersecting polygons.    
     
     
         31 . A fuel cell stack according to  claim 30  wherein: 
 one of said intersecting polygons is a rectangle.    
     
     
         32 . A fuel cell stack according to  claim 30  wherein: 
 two of said intersecting polygons are rectangles.    
     
     
         33 . A fuel cell stack according to  claim 30  wherein: 
 one of said intersecting polygons is a triangle.    
     
     
         34 . A fuel cell stack according to  claim 5  wherein: 
 said coolant passageways comprise coolant channels extending from said second surface of one of said flow field plates and a layer of material, highly permeable to coolant, disposed between and substantially coextensive with adjacent ones of said flow field plates in said stack.    
     
     
         35 . A fuel cell stack according to  claim 34  wherein: 
 said channels are either (a) substantially rectangular or (b) shaped to have a gas tolerant cross section.    
     
     
         36 . A fuel cell stack according to  claim 5  wherein: 
 the cross section of each of said passageways comprises the intersection of a first groove, extending from said second surface of said fuel reactant gas flow field plate and a second groove, smaller than said first groove, extending from said first groove toward said first surface of said fuel reactant gas flow field plate.    
     
     
         37 . A fuel cell stack according to  claim 5  wherein: 
 said coolant passageways are at least one of (a) within reactant gas flow field plates and (b) adjacent to reactant gas flow field plates.    
     
     
         38 . A fuel cell stack comprising: 
 a plurality of fuel cells having reactant gas flow field plates;    a coolant flow path extending to a plurality of fuel cells in said stack; and    coolant passageways within said coolant flow path substantially coextensive with planforms of said fuel cells and at least one of (a) within said reactant gas flow field plates and (b) adjacent to said reactant gas flow field plates, said coolant passageways configured to provide portions with high capillary pressure extending along substantially the entire length of said passageways.