On-Board Hydrogen Powered Proton Exchange Membrane Fuel Cells

Abstract

One of the main concerns in the commercialization of fuel cell powered electrical vehicles is the on-board storage of hydrogen. Although pressurized vessels used in conventional systems provide higher hydrogen feeding rates, they have disadvantageous due to their extra weight and higher volumes in the systems. In this study, we report direct hydrogen generation from chemical hydrides, which does not require pressurized vessels. Self-dehydrogenation of chemical hydrides is a very slow process. In order to increase hydrogen generation kinetics, highly active and stable catalysts should be used. Although precious catalysts such as platinum and ruthenium meet these demands, their higher cost and recycling problems make them less useful in the fuel cell area. A novel approach will be presented here for the fast, safe and stable hydrogen generation for fuel cells. This was achieved by circulating the acid and the chemical hydride solutions which were separated by the disulfonated poly(arylene ether sulfone) copolymer membrane. Since the rate of proton transfer is a function of ion exchange capacity (IEC) and scales with the degree of disulfonation of membranes, tailoring the IEC of membranes is crucial during the hydrogen generation. Therefore, membranes with varying sulfonation degrees (25-45 molar %) have been prepared and their hydrogen generation rates have been evaluated. Additionally, it was found that the type of acid and acid concentration influenced the hydrogen generation rates. The effect of temperature on hydrogen generation performances was also investigated. When temperature exceeded the 80 °C, the hydrogen generation performance of N212 (the state of art membrane, Nafion™) was decreased due to the morphological changes occurred at this temperature. However the performances of our membranes without morphological relaxations continued to increase at higher temperatures. Furthermore, we run a proton exchange membrane fuel cell with our hydrogen generator and demonstrated continuous hydrogen generation more than 400 h. As a result, highly efficient on-board hydrogen generator for electrical vehicles powered by fuel cells presented here completely eliminates the need for separate facilities for producing hydrogen.