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Critical Factors to Achieving an Optimised System - Contact Resistance and Surface Roughness
Whilst remaining chemically “passive”, bipolar plates must provide a low resistance path for electron migration within the fuel cell stack. In order to exploit the true potential of the fuel cell stack, the surface science of bipolar plates requires great consideration. This includes an understanding of the homogeneity in surface material, in-plane conductivity, plate porosity, degree of planarity and surface roughness. Of the many vital surface properties, roughness has a major impact on overall stack power efficiency. An extremely rough surface can limit the interfacial interaction with the Membrane Electrode Assembly (MEA). Put simply, by minimising the bipolar plate surface roughness, you reduce the interfacial resistance (for a given stack compression).
By relying on an insulating polymer matrix, most composite bipolar plate manufacturers require secondary surface operations to remove a non-conducting surface coating. General surface treatments will only increase the surface roughness when compared to the high quality, moulded surface finish. However the high post-moulding resistive layer has a negative impact on the output performance of a fuel cell stack, where the degree of surface resistance is directly proportional to the interfacial efficiency of current transfer in a fuel cell stack. These manufacturers must remove the detrimental, electrically insulating coating and accept that the plate’s interfacial contact area will always be limited by the additional surface processes. These operations include surface machining, chemical etching and pressurised water ablation, which all adding significant cost to the final product.
A critical question is then posed - is it possible to overcome this problem, especially when considering larger volume scale-up and mass production? Fortunately the answer is yes - Bac2 Ltd has solved this issue without the need for surface modification. Bac2 Ltd utilise the patented conductive polymer, ElectroPhen®, as a host binder. The intrinsic conductivity in this host polymer matrix removes any necessity for additional surface treatment or secondary processing.
Key Points:
- Moulded plates have a smoother surface finish than machined plates
- ElectroPhen plates do not need surface machining
- Moulded plates offer a cost advantage as well as performance
- Moulded plates can improve consistency of stack performance
We are interested to talk with fuel cell developers to help understand the benefits to system performance of our moulded plates.
Please see attached White Paper for further details
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