Fabrication of function-graded proton exchange membranes by electron beam irradiation for polymer electrolyte fuel cells under nonhumidified condition

Function-graded proton exchange membranes (G-PEMs) for polymer electrolyte fuel cells (PEFCs) are fabricated by electron beam (EB) grafting using a heterogeneous energy deposition technique. The fabricated G-PEMs have a water uptake gradient in the direction of the thickness originating from the sulfonic acid group gradient. Normal PEMs (N-PEMs), which have almost no gradient ionic groups in the membrane, are also fabricated to compare with G-PEMs. PEFC operations for comparing the fabricated G-PEMs, normal PEMs (N-PEMs), and Nafion^®212 are carried out at 30 C and 60 C with dry H ₂/O₂ gases. It is expected that the advantages of using dry fuel gases are lower cost and a smaller size system than that is possible with a humid fuel. The fabricated G-PEMs show a higher power density than Nafion^®212 and N-PEMs at 30 C, and the deterioration of the performance of fabricated G-PEMs is lower than that of Nafion ^®212. These results are thought to be caused by the difference in proton transfer kinetics between the fabricated G-PEMs and those of Nafion ^®212. It is therefore considered that G-PEMs not only exhibit higher performance at low temperature under nonhumidified conditions but also cost less than Nafion^®212.