Highly conductive composites for fuel cell flow field plates and bipolar plates

Abstract

This invention provides a fuel cell flow field plate or bipolar plate having flow channels on faces of the plate, comprising an electrically conductive polymer composite. The composite is composed of (A) at least 50% by weight of a conductive filler, comprising at least 5% by weight reinforcement fibers, expanded graphite platelets, graphitic nano-fibers, and/or carbon nano-tubes; (B) polymer matrix material at 1 to 49.9% by weight; and (C) a polymer binder at 0.1 to 10% by weight; wherein the sum of the conductive filler weight %, polymer matrix weight % and polymer binder weight % equals 100% and the bulk electrical conductivity of the flow field or bipolar plate is at least 100 S/cm. The invention also provides a continuous process for cost-effective mass production of the conductive composite-based flow field or bipolar plate.

Description

[0001] The present invention is based on the research results of a project supported by the US Department of Energy SBIR-STTR Program. The US government has certain rights on this invention.FIELD OF THE INVENTION [0002] The present invention provides a highly electrically conductive composite material for use in a fuel cell bipolar plate or flow field plate. BACKGROUND OF THE INVENTION [0003] A proton exchange membrane (PEM) fuel cell is typically composed of a seven-layered structure, including (a) a central PEM electrolyte layer for proton transport; (b) two electro-catalyst layers on the two opposite primary surfaces of the electrolyte membrane; (c) two fuel or gas diffusion electrodes (GDEs, hereinafter also referred to as diffusers) or backing layers stacked on the corresponding electro-catalyst layers (each GDE comprising porous carbon paper or cloth through which reactants and reaction products diffuse in and out of the cell); and (d) two flow field plates (or a bi-polar plat...

AI Technical Summary

Benefits of technology

[0020] This invention provides a fuel cell flow field plate or bipolar plate having flow channels on faces of the plate, comprising an electrically conductive polymer composite. In one preferred embodiment, the composite is composed of (A) at least 50% by weight of a conductive filler, comprising at least 5% by weight reinforcement fibers, expanded graphite platelets, graphitic nano-fibers, and/or carbon nano-tubes (this at least 5% is based on the total weight f the composite); (B) thermoplastic at 1 to 49.9% by weight; and (C) thermoset binder at 0.1 to 10% by weight; wherein the sum of the conductive filler weight %, thermoplastic weight % and thermoset binder weight % equals 100% and

Problems solved by technology

The bipolar plate is known to significantly impact the performance, durability, and cost of a fuel cell system.

The bipolar plate, which is typically machined from graphite, is one of the most costly components in a PEM fuel cell.

These methods of fabrication place significant restrictions on the minimum achievable fuel cell thickness due to the machining process, plate permeability, and required mechanical properties.

Further, such plates are expensive due to high machining costs.

The machining of channels into the graphite plate surfaces causes significant tool wear and requires significant processing times.

Such laminated fluid flow field assemblies tend to have higher manufacturing costs than integrated plates, due to the number of manufacturing steps associated with forming and consolidating the separate layers.

They are also prone to delamination due to poor interfacial adhesion and vastly different coefficients of thermal expansion between a stencil layer (typically a metal) and a separator layer.

Because most polymers have extremely low electronic conductivity, excessive conductive fillers have to be incorporated, resulting in an extremely high viscosity of the filled polymer melt or liquid resin and, hence, making it very difficult to process.

It is well-k

Images