Ionic Conductivity of an Extruded Nafion 1100 EW Series of Membranes

Abstract

The proton conductivity of a series of extruded Nafion membranes ͓of equivalent weight ͑EW͒ of 1100 and nominal dry thickness of 51, 89, 127, and 178 m͔ has been studied. Measurements were made in 1 M H 2 SO 4 at 298 K using a four-electrode, dc technique. The membrane area resistance increases with thickness, as expected, from 0.07 to 0.16 ⍀ cm 2 for Nafion 112 and Nafion 117, respectively. However, in contrast to the published literature, after correcting for the membrane thickness, the conductivity of the membranes decreases with decreasing membrane thickness. For example, values of 0.083 and 0.16 S cm Ϫ1were obtained for Nafion 112 and 117 membranes, respectively. In situ current-interrupt measurements in a proton exchange membrane fuel cell confirmed the relatively poor conductivity of the membrane electrode assemblies ͑MEAs͒ based on the thinner membranes. While a high contact resistance to the electrodes may have contributed to the in situ MEA resistance, water balance measurements over the MEA showed that the high resistance was not due to a low water content or to an uneven water distribution in the MEAs. The implications of the findings for the understanding of the membrane properties are discussed. Nafion membranes.-Nafion membranes have a wide range of applications due to their high chemical and electrochemical stability, reasonable mechanical strength ͑particularly when reinforced͒, extremely low permeability to reactant species, selective and high ionic conductivity, and their ability to provide electronic insulation. Industrial applications of these materials involve industrial sectors such as gas separation, gas sensors, electrodialysis, chlor-alkali cells, salt splitting, and as a solid polymer electrolyte in fuel cells and batteries. [2][3][4] This study has focused on the application of the Nafion range of cation-exchange membranes in proton exchange membrane fuel cells ͑PEMFCs͒. In the PEMFC the proton conductivity of the membrane is particularly important since it plays a significant role in controlling the performance of the fuel cell. 5,6 Higher levels of proton conductivity allow much higher power densities to be achieved. This is particularly important for automotive applications of PEMFCs. The two common strategies to improve the conductivity of the membrane are to raise the specific conductivity and to reduce the thickness. There is, however, a practical limit on the thickness since, much below 25 m, mixing of the hydrogen and air ͑or oxygen͒ reactant gasses due to crossover through the ion-exchange material is too high for pure Nafion membranes and there is a loss of efficiency. Reducing the membrane thickness also increases the risks with respect to mechanical properties such as strength, raising concerns regarding the durability and ease of handling of the membranes.The structure of Nafion membranes.-The proton conductivity of Nafion membrane materials is complex, being favored by a high level of hydration and being strongly dependent on the pretreatment ͑especially the thermal͒ his...

The Ionic Conductivity of a Nafion® 1100 Series of Proton‐exchange Membranes Re‐cast from Butan‐1‐ol and Propan‐2‐ol

“…Full details of the experimental procedure and a discussion of the problems associated with obtaining reliable measurements have been described in ref. [23].…”

“…The volume of NaOH consumed was used to calculate the amount of H + in solution. Assuming complete conversion of the membrane to the Na + form, the ion-exchange capacity (IEC, mmol H + / g polymer) was calculated [4,23,25]:…”

“…1 The glass, four-electrode cell used to measure the membrane resistance of a circular sample (1 cm 2 ) using a steady state, d.c. linear sweep galvanodynamic technique. The resistance value was corrected by measuring the uncompensated IR drop resistance between the two Luggin capillaries fitted with a SCE reference electrode in the absence of a membrane [23].…”

“…The membrane thicknesses produced were of the same order of magnitude as those of an extruded Nafion ® series of materials [23]. The relationship between the ionic conductivities of the cast and extruded membranes and the effect of hot-pressing the membranes are considered as well as the performance differences associated with the method of membrane manufacture.…”

Evaluation of polymer electrolyte membrane fuel cells by electrochemical impedance spectroscopy under different operation conditions and corrosion

“…Yuan et al [1] reported EIS has already become a primary tool in PEMFC research. EIS method is also used effectively for analyses of the amount of catalysts [2][3][4][5], nafion content [3,[6][7][8], membrane thickness [9,10], GDL structure [11][12][13][14][15][16][17][18][19], proton conductivity [20][21][22][23][24][25][26], humidification condition [3,9,[27][28][29][30] and stack [24,[31][32][33][34][35][36]. For example, Paganin et al [2] and Song et al [3] suggested that charge transfer resistance is much smaller with increasing amount of catalysts.…”