Extending the Life-Time of Low Cost Fuel Cells

Abstract

Extending the bipolar plate lifetime of low-cost fuel cell. Energy conversion sources that offer lower carbon emissions, increased efficiency and reduced environmental impact at a competitive cost are a key requirement for future low carbon transport and stationary power generation applications.Fuel cells are promising candidates but widespread uptake has so far been hindered by the high cost of materials and manufacturing in addition to limited durability under realistic operating conditions. There is a clear need for a lower cost approach but without sacrificing performance or durability. Bipolar plates are responsible for collecting current, supplying the fuel to the MEA as well as exhausting water produced at the cathode side1. Metallic bipolar plates must be resilient, non-porous, conductive with a low contact resistance and obviously cheap for mass market penetration2. The US Department of Energy (DoE) has introduced target cost plans for 2020 on different PEM fuel cell components, including bipolar plates3. The technical plan states that the corrosion rate must be below 1 µA.cm-2 and that an interfacial contact resistance must be below 10 mΩ.cm2 at a compaction pressure of 140 N.cm-2. These condition has to be attained with a cost below 3 $kW-1. Bipolar plates account for 45-60 % of the stack cost, 80 % of the weight, and almost all the volume of the PEM fuel cell stack. The flexiplanar approach uses a metallic substrate mounted on a printed circuit board (PCB) in order to produce a low cost cell. Copper is a strong candidate for this purpose: it is robust, has a high conductivity and a low contact resistance as well as a possibility of scalable hydroforming or stamping4, which is an important feature in order to produce a flow field plate. However, due to the harsh conditions within the fuel cell stack such as a high potential and temperature, the copper interface must be protected by a coating. Coatings applied on the flow field plate must have a good electrical conductivity, a low contact resistance and also have to be resilient to fuel cell operating conditions i.e. 120 °C and 1.2 V. In recent years, there has been an increasing amount of literature on carbon polymer blend used as metallic substrate protector19 , 20 , 21. Carbon-polymer mixtures are commercially available at reasonably affordable prices. Nevertheless, they are also likely to be corroded due to carbon micro-particles dispersed in the polymer. Hence further investigation needs to be done in this poorly understood area. 1 Polymer Fuel Cells - Cost reduction and market potential, C. Trust, 2012. 2 C. Spiegel, Designing and Building Fuel Cells, 2007. 3 T. Plan and F. Cells, 2015, 1–49. 4 ASM International, Copper and Copper Alloys, ASM International, 2001. 5 W. L. Wang, S. M. He and C. H. Lan, Electrochim. Acta, 2012, 62, 30–35. 6 Y. Show and K. Takahashi, J. Power Sources, 2009, 190, 322–325. 7 Y. B. Lee and D. S. Lim, Curr. Appl. Phys., 2010, 10, S18–S21.