Fuel cells

Résumé du document

What are the limiting factors in the introduction of PEM fuel cells into mobile power generation? What areas of research are being carried out to address these limitations and which of these do you feel will have the biggest impact in enabling the various types of fuel cells systems? Proton Exchange Membrane (PEM) fuel cells have first been developed in the 1960s by General Electric to be used on their first NASA manned vehicles (Gemini program)[1]. Then different kind of fuel cells has been experimented, for different purposes but they have never been produced in large quantities. Nevertheless, in the last decades, with the new concerns about global warming, green house gases as CO2 and pollution, their development skyrocketed and huge improvements have been made. Indeed fuel cells are a "clean" technology, as no harmful exhaust emissions are produced (the only products are pure water and heat), and the only CO2 emissions would be made when producing electricity to obtain hydrogen [2]. With a renewable energy source to produce electricity, no CO2 at all would be produced. An example with fuel cells vehicle is shown on figure 1.

Extraits

[...] In the other different attempts to develop low cost membranes, good results have also been obtained with non fluorinated polymers and zirconium phosphonates, which are still currently in a development phase, and face the same problem of performance as the technologies described earlier Another key challenge addressed by researchers is the produced water management, which has to be more efficient to enhance the fuel cell performance. Thanks to Computational Fluid Dynamics models, they try to better understand the phenomena in which the water is produced and then moved through the fuel cell. A better understanding would lead to a better control of this process and then to possible improvements of the operation of the PEM fuel cell. Conclusion PEM fuel cells performance are seen like the most promising technology, which could become the most used way to power mobile applications in the future. [...]

[...] This can be explained by several limiting factors inherent to this technology. Indeed the cost of the PEM fuel cells is very high, mainly due to the high cost of the membrane and of the catalyst. Lifetime of the fuel cell is also seen as a limiting factor, and even if the efficiency of fuel cells systems is higher than a lot of its counterparts, fuel cell low power density still entail issues and is related to the high costs. [...]

[...] Thus the amount of catalyst and membrane material needed increase, and finally costs increase too. Hydrogen related issues 1 High cost and low availability of hydrogen Supplying a fuel cell powered mobile device with hydrogen is currently a costly process, and it is believed that the success of PEM fuel cells development (especially for transportation purposes) mainly depends on the creation of a reliable and cost-effective hydrogen supply industry Producing hydrogen (most of the time by electrolysis of water) consumes electricity which entails costs (and CO2 emissions also if electricity is produced from fossil fuel fired power plants) and makes hydrogen still more expensive than conventional fuels, as gasoline for instance. [...]

[...] As instance the use of Single Wall carbon NanoTubes (SWNTs), both for hydrogen and methanol fuel cells are under consideration in different research institutes. The better mechanical properties and corrosion resistance of these nanotubes may enhance the overall performance fuel cell performance. This technology seems especially promising because apart from the enhanced performance, it reduces the amount of catalyst needed at the cathode, and consequently decreases the cost of the cell. Research currently aims at accurately defining the properties of such systems [17]. [...]

[...] New studies are still needed in order to accurately assess these technologies, and the most efficient way to produce and use them & but to my mind, they are currently the most promising solutions to the hydrogen storage problem. Research on new MEA technologies As we saw in the previous part, the most important costs in a fuel cells are entailed by the membrane and by the need to use the expensive platinum catalyst. To decrease the cost of the catalyst used in the PEM fuel cells, researchers try to develop a mixture of platinum and ruthenium to replace the expensive platinum. This new catalyst would be needed in smaller quantity for the same efficiency. [...]