A British innovation promises to boost the power available from fuel cells, and bring down the manufacturing costs.
The breakthrough is in the design of the bipolar plates that are a key component of a fuel cell. The patented ‘Biomimetic’ bipolar plate technology developed by Morgan Fuel Cells (MFC) drew its inspiration from the natural world. It mimics the structure seen in animal lungs and plant tissues to allow the gases to flow through the plate in a far more efficient way than had been achieved before.
Bipolar plates themselves serve two principal roles in the fuel cell. One purpose is to act as a conductor for the electrical energy. A second purpose is to channel the flow of gases to ensure that the electrode is adequately supplied with reactants. The gases flow in a number of finely detailed convoluted flow field channels, typically 0.5 to 2 millimetre wide and up to 1 millimetre deep, formed in the surface of the plate.
Dr. Mark Turpin, Global Director of Technology for MFC, explains: ‘We realised by looking at how animal lungs and plant leaves ‘breathe’, that a structure consisting of large distribution channels feeding progressively smaller capillaries is the most efficient way to distribute reactants.
‘So we mimicked this approach in the Biomimetic plate, with a highly branched flow field that distributes gas through a fine system of capillaries. This structure reduces the pressure drop found in the industry-standard serpentine design of flow field and ensures a more even delivery of gas across the bipolar plate, so that more power can be extracted from the fuel cell. Initial results are very promising, with tests already confirming a 16% increase in peak power, and we are certain that even more significant improvements can be made.’
Using a Biomimetic flow field pattern also offers the possibility of significant indirect performance and cost benefits. These include improved water management (water being a by-product of the fuel cell process) and reduced overall pressure requirements.
MFC has focused mainly on the graphite bipolar plates featured in PEM (proton exchange membrane) type fuel cells used typically in automotive and general power replacement applications. However, Biomimetic flow field designs are potentially applicable to ceramic and metal bipolar plates and the core design has been adapted for use in direct methanol fuel cells and may find applications within solid oxide fuel cell systems too.
Key to the creation of the Biomimetic plate design is MFC’s patented ElectroEtch manufacturing technology, which uses a grit blasting technique to produce a plate in a matter of minutes. This offers a rapid prototyping capability, from drawing to finished plate in about two hours, which enables many different plate designs to be evaluated. And there is no extra cost for complexity, as it takes the same time to etch a complex pattern as a simple one.