Design and Manufacture of Metal Foam Flow Fields for Proton Exchange Membrane Fuel Cell

This project investigates metal foam for use as the flow field in automotive, Proton Exchange Membrane Fuel Cells (PEMFCs). Metal foams are typically used as high temperature filters, low density mechanical structures, or high specific area substrates for chemical reactions. The properties that are required by those applications are not necessarily those that lead to high performing PEMFCs. Furthermore, the range of achievable metal foam properties are constrained by the available foam manufacturing techniques, with any given manufacturer's off the shelf product line necessarily being available in only some limited discrete combinations of properties. To optimize metal foam fuel cells, it is necessary to determine which foam properties have the greatest effect on PEMFC performance, and how to process commercially available foam to achieve these properties.;Two critical material properties which affect the performance of fuel cell flow fields are the electrical resistance and the permeability. Two different off the shelf metal foams (differing in their porosity and pore size) were plastically compressed by different amounts, and coated by dipping in different concentrations of PTFE solution. The electrical conductivity and permeability of these foams were measured to determine which of these three factors were affecting these material properties with statistical significance. Based on these results, fuel cells were constructed with different foam flow fields, and their performance was evaluated. The liquid water distribution in these cells was determined with neutron imaging.;The foam processing factor which had the greatest effect on both permeability and resistance was the amount of compression. Over the ranges tested, the foam permeability ranged from 1.2E-9 to 5.0E-11 m2 and the total foam resistance ranged from 0.39 to 0.44 ohm-cm2 (at a compression stress of 0.5 MPa and the foam contacting GDL and bare copper). The power output of the best performing fuel cell flow field (metal foam with a thin coating of PTFE) had a power density of ~1amp/cm2, approximately three times that of the channel flow field cell.;The neutron images showed that fuel cells with more liquid water had less performance stability. The foam with the thicker PTFE coating was better at expelling water, indicating that the foam hydrophobicity was affecting the fuel cell performance.