New Multi Acid Side-Chain Ionomers for Proton Exchange Membrane Fuel Cells

Schaberg, Mark S.; Abulu, John E.; Haugen, Gregory M.; Emery, Michael A.; O'Conner, Sara J.; Xiong, Pa N.; Hamrock, Steven J.

doi:10.1149/1.3484559

Cited by 55 publications

(69 citation statements)

References 5 publications

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“…Perfluoro bis(sulfonyl)imides have been suggested for use as polymer electrolytes and offer the potential to be used as both an additional acid functionality and a side chain extender. 11,12 This…”

Section: New Ionomersmentioning

confidence: 92%

Increasing Fuel Cell Efficiency by Using Ultra-Low Equivalent Weight Ionomers

Yandrasits¹,

Lindell²,

Schaberg³

et al. 2017

Electrochem. Soc. Interface

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humidity. Interestingly, the slope of the PFIA and PFICE-4 lines (on a log scale) were approximately parallel to each other and to the PFSA controls. Why All the Trouble to Develop New Ionomers?The objective of this work was to increase the proton conductivity of the ionomer while maintaining a water-insoluble membrane with good physical integrity. By starting with a perfluoro sulfonyl fluoride polymer backbone of 700 or 800 g/mol, it was our expectation that the backbone crystallinity would remain, and, therefore, the water insolubility, while the ion exchange capacity would increase. In other words, each additional bis(sulfonyl)imide functionality increased the overall acid content but left the backbone unchanged.It is clear from Fig. 3 that the ionic conductivity increased with these new ionomers over all humidity ranges, but it is worth considering the implications of these improvements in actual fuel cell operating conditions. Starting with the higher humidity conditions at 90% RH, the conductivity of the PFIA ionomer was over two times higher than Nafion (335 vs. 147 mS/cm) and nearly four times higher for the PFICE-4 ionomer (567 vs. 147 mS/cm). Making a few simple assumptions, such as a 20 μm thick membrane and operating at 1.5 A/ cm 2 , voltage loss due only to membrane resistance at these conditions can be calculated using Ohm's law (V=I*R). For the Nafion membrane the voltage loss was calculated to be 20 mV, the PFIA about 9 mV and the PFICE-4 about 5 mV. While these differences can be significant at times, they represent only a modest improvement at best and would not likely justify the additional effort and cost associated with these new, ultra-low equivalent weight ionomers. However, looking at the other end of the humidity range, where the conditions are significantly drier, the same comparisons were made with dramatically different conclusions. At 30% RH the ionic conductivities of Nafion, PFIA and PFICE-4 membranes were 11, 44, and 70 mS/cm, respectively. Using these values in the same analysis as above, the voltage loss due to membrane resistance at a current density of 1.5 A/cm 2 was calculated to be 275, 68, and 43 mV respectively. This several hundred millivolt reduction in voltage loss due to lower membrane resistance can be put into context by converting these values into loss of efficiency. For instance, one simple measure is the ratio of the calculated voltage loss to the equilibrium potential of the hydrogen-oxygen reaction (1.23 V). Under fully hydrated conditions, the efficiency loss due to membrane resistance only was 1.7, 0.7 and 0.4% for Nafion, PFIA, and PFICE-4 respectively. Again, these differences may be significant in some situations but are generally very small values. The more interesting case, however, is where the membrane humidification is low. For the Nafion membrane a 22% efficiency loss was calculated. This value is unacceptable and would generally prevent a system design that would be expected to operate at these dry conditions. PFIA membrane provides a much larger co...

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Section: New Ionomersmentioning

confidence: 92%

Increasing Fuel Cell Efficiency by Using Ultra-Low Equivalent Weight Ionomers

Yandrasits¹,

Lindell²,

Schaberg³

et al. 2017

Electrochem. Soc. Interface

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show abstract

“…The PFIA ionomer was synthesized in our laboratory using methods described elsewhere and has an equivalent weight of 620 g/mol. 6 Two constructions of membranes were studied for each ionomer; constructions typical of commercial membranes that included a nanofiber support 23,24 and peroxide-scavenging additives, 13 and neat membranes with no support or additives (Table I). All membranes used in this study were fabricated at 3M using the same manufacturing methods and equipment.…”

Section: Methodsmentioning

confidence: 99%

Chemical Stability of Perfluorobis(sulfonyl)imide-Acid (PFIA) Ionomers in Open Circuit Voltage (OCV) Accelerated Test Conditions

Yandrasits

Lindell

Peppin

et al. 2018

J. Electrochem. Soc.

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Membranes based on 3M's perfluoro imide acid (PFIA) ionomer have been studied using the open circuit voltage (OCV) hold accelerated stress test. For these samples, a decay in the OCV potential within the first 200 hours was observed along with an increase in cell resistance that rapidly grows near the end of life. A multi-membrane electrode assembly (MEA) technique was employed to study the origins of these phenomena. Effluent water collected at the beginning of life and later, during a recovery protocol, was analyzed using liquid chromatography -mass spectroscopy (LC-MS). A variety of small molecule fragments were detected that could be traced to the ionomer side chain. The center layer of a three-membrane MEA was separated at the end of life and analyzed by 19 F nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. Peaks associated with the bis(sulfonyl)imide group of the PFIA ionomer were observed to have reduced in intensity and new peaks, assigned to a perfluorosulfonamide side chain, appeared. The combination of the fragments detected in the effluent water, along with the spectral changes in the membranes after aging, point to one or more degradation processes involving the PFIA ionomer side chain. This decomposition is likely analogous to reactions described for perfluorosulfonic acid (PFSA) ionomers but with new consequences owing to the greater number of potential fragments.

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“…2,3 Efficient electrochemical reduction of oxygen at the cathode of the FC requires stable and inexpensive catalysts 2,4,5 and improved durability with high proton conductivity electrolyte membranes that perform well under hot and dry conditions. [6][7][8][9][10] NAFIONt membranes with a hydrophobic tetra-fluoroethylene (PTFE) backbone and hydrophilic pendant chains terminating in sulfonate groups are still the most commercially used PEMs in the FC industry. 11,12 The molecular structure of water confined inside the channels of NAFIONt membranes has been extensively studied at different hydration stages and is influenced by the size of water channels formed due to clustering of the hydrophilic sulfonic acid groups or by the closeness to the hydrophobic polymer backbone.…”

Section: Introductionmentioning

confidence: 99%

“…18,[21][22][23] The hydrated hydronium ions are found in Zundel 24 26 Recent developments towards improved PEM performance reported use of multi acid side chains to retain high proton conductivity, stabilizing additives for improved chemical or polymer nanofibers for mechanical stability. 8,10,27 Having multiple acidic sites per side chain lowers the ionomer equivalent weight (EW = grams of ionomer per mole of acid) without compromising the mechanical stability and allows for the formation of larger ionic channels which increases proton conductivity. 28 Perfluoroimide acid or PFIA is one of these multi-acid PEMs recently developed by the 3M Company's (3M) Fuel Cell Components Group that incorporates a bis-sulfonyl imide group into pendant chains providing an additional source of the protonic group (Scheme 1A, compare Scheme 1B for NAFIONt).…”

Section: Introductionmentioning

confidence: 99%

“…28 Perfluoroimide acid or PFIA is one of these multi-acid PEMs recently developed by the 3M Company's (3M) Fuel Cell Components Group that incorporates a bis-sulfonyl imide group into pendant chains providing an additional source of the protonic group (Scheme 1A, compare Scheme 1B for NAFIONt). 8 Bis-sulfonyl imide is known to have an acid strength even higher than the terminal sulfonic acid in the gas phase. 29 PFIA was reported by 3M as high performing with the low EW 625 but significant backbone crystallinity equivalent to ionomers of EW 1000.…”

Section: Introductionmentioning

confidence: 99%

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Infrared dynamics study of thermally treated perfluoroimide acid proton exchange membranes

Puškar

Ritter

Schade

et al. 2017

Phys. Chem. Chem. Phys.

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The temperature induced dehydration process of the 3M Brand perfluoroimide acid (PFIA), an advanced proton exchange membrane for fuel cells, was studied by in situ infrared spectroscopy to understand proton transport processes under conditions of low hydration levels. A comprehensive assignment of the vibrational bands of PFIA in the mid infrared region is provided. Investigation of the kinetics in conjunction with 2D correlation spectroscopy methods revealed the sequential process of the hydration and dehydration in a conclusive model. The results indicate that at a lower water content the sulfonate group of the PFIA side chain is preferentially ionised and involved in a hydrogen bonding structure with the sulfonyl imide acid group, until a sufficient amount of water is present to ionise the second ionic site. Comparison to the well-understood NAFION™ membrane revealed that under low humidity conditions a higher amount of water is retained in PFIA in a state most similar to liquid water. The results contribute to a better understanding of water retention capability and thus proton conductivity under high-temperature and low-humidity conditions.

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New Multi Acid Side-Chain Ionomers for Proton Exchange Membrane Fuel Cells

Cited by 55 publications

References 5 publications

Increasing Fuel Cell Efficiency by Using Ultra-Low Equivalent Weight Ionomers

Increasing Fuel Cell Efficiency by Using Ultra-Low Equivalent Weight Ionomers

Chemical Stability of Perfluorobis(sulfonyl)imide-Acid (PFIA) Ionomers in Open Circuit Voltage (OCV) Accelerated Test Conditions

Infrared dynamics study of thermally treated perfluoroimide acid proton exchange membranes

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