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ITM Power achieves automotive high power density fuel cell performance objectives in 9-month test program
4 October 2011
UK-based ITM Power has released a summary of the results of a recently completed 9-month fuel cell project that evaluated the company’s proprietary hydrocarbon membrane materials in high power density hydrogen/air fuel cells. The project was supported by the Carbon Trust as part of the Polymer Fuel Cells Challenge. The project objectives, which were defined by automotive industry experts, were all achieved, ITM Power said.
Increasing power density is a critical factor in reducing the cost of fuel cells. ITM Power’s materials have shown the ability to generate high power density when using either oxygen (>5.5W/cm2) or air (>2.1W/cm2). Unlike the majority of conventional fluorocarbon membrane materials which are expensive and require significant chemical plant to fabricate, ITM’s materials are low-cost hydrocarbons made by mixing together liquid chemicals to a particular recipe.
The project examined the impact of operating in environments and conditions required by the automotive industry. This included sensitivity to reduced catalyst loading, gas pressure, humidity, temperature and stoichiometry. In addition, longevity studies were initiated and benchmarking was carried out against industry standard materials.
The project was undertaken at a single test cell level and sought to reduce the technical risk presented by ITM Power’s materials as a new component.
Power density. During the course of the project, the fuel cell power density when using air was increased by one order of magnitude. Catalyst loadings as low as 0.38mg/cm2 have been successfully operated with dry gases down to 0.34bar (5psi) pressure. In addition, high power density has been developed at higher cell voltages providing higher overall conversion efficiency. Results include:
- Power density of 1.5W/cm2 at >600mV
- Power density of 1.0W/cm2 at >700mV
- Membrane conductivity over three times that of industry standard membranes
- No irreversible degradation during short durability tests
ITM Power’s materials retain high power densities at the low catalyst loadings and reduced operating pressures that the automotive industry requires. This is in addition to the other positive attributes of ITM Power’s materials, including reduced cost and ease of manufacture, the company noted.
Durability results. Durability results are highly dependent on cell structure and flow field design. It was a challenge to maintain the process conditions within the test cell using existing equipment to undertake extended durability tests. However, during the evaluation programme, no irreversible degradation was observed when comparing ITM Power’s MEA (membrane electrode assembly) performance before and after testing, the company said. While high MEA efficiencies are achieved, the unusually high current densities present new challenges in terms of flow field and electrode design.
An important challenge facing fuel cell membrane materials is the ability to maintain adequate water content for effective ionic conduction. This often necessitates the use of balance of plant to humidify input gas streams. ITM Power says that one of the advantages offered by its fuel cell materials is an additional hydrophilic component which serves to hold water inside the polymer structure and rendering it extremely water attracting and less prone to drying. The key power density performance data presented was achieved with dry gases.
Mechanical properties and dimensional stability. ITM Power’s materials are cross linked. This provides good dimensional stability and contributes to robust overall mechanical properties. In addition, the ITM Power material has an ionic conductivity over three times that of industry standard membranes. This allows comparatively thick membranes to be used adding further mechanical robustness. As the membrane material is cast from a liquid mixture, it is compatible with reinforcing structures such as webs, cloths or mats.
Demountable structure and catalyst recycling. The catalyst needs to make good interfacial contact with the membrane for effective MEA function. The nature of ITM Power’s materials offers multiple convenient routes for achieving excellent contact. Firstly, the membrane material is very compliant and so enables a simple pressed contact within the cell to deliver exceptional performance without the need for a hot pressing stage. This in turn offers a way to reclaim catalyst easily at the end of MEA life. Furthermore, recycling hydrocarbon materials is much easier than for fluorocarbons as there is no release of fluorine or hydrofluoric acid.
Manufacturing routes. ITM Power’s materials are polymerized by ultraviolet light, a low-cost process which is compatible with volume production techniques and well understood by industry. There is no requirement to add an additional hot pressing stage to MEA fabrication as catalyst-coated electrodes make excellent contact in a simple pressed arrangement. Multiple routes for incorporating catalyst structures into the surface of the membrane during the polymerization process have been explored and shown to be viable. In addition, spraying an ink containing ITM Power’s ionomer onto a pre-cured membrane is possible. ITM Power is exploring partnering with large polymer processing companies.
Industry performance targets. Commercial rollouts of fuel cell electric vehicles (FCEVs) is scheduled to begin in 2015 and the industry has set a number of challenging performance and cost targets as guidelines for the fuel cell supply chain. One review, undertaken by Germany’s National Organization for Hydrogen and Fuel Cell Technology (NOW, Nationale Organisation Wasserstoff- und Brennstoffzellentechnologie), identified a performance target of 1W/cm2 at 670mV as being an aspiration for OEMs. The same report concluded that the performance was not currently achievable. ITM Power says it has exceeded this power density target.
Performance and full life cost modeling. The results obtained by ITM Power’s materials will be independently analysed via a comprehensive cost model developed by the Carbon Trust. This will enable costs to be projected and described in $/kW. The outcome of these analyses will be made available once complete. Durability results will be the last step in understanding the full life cost advantages of the ITM Power membrane technology.
Commercialization and business model. ITM Power intends to commercialize its novel MEAs using a licensing business model.
This project has been a huge success. The progress made by ITM Power over the course of 9 months is significant and is testament to the capability of its materials technology. The Carbon Trust is delighted to have assisted with this achievement and looks forward to providing further introductions and downstream industry cost analysis.—Robert Trezona, Technology Director, the Carbon Trust
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