Sulfonated Polyphosphazene-Polybenzimidazole Membranes for DMFCs
Open accessAbstract
Proton-conducting membranes were prepared from blends of sulfonated poly[bis(phenoxy)phosphazene] (SPOP) and polybenzimidazole (PBI), where the latter was used as a cross-linking component. The membranes were evaluated in terms of room-temperature water swelling and proton conductivity, methanol permeability at 60°C, and direct methanol fuel cell (DMFC) performance at 60°C with a 1.0 M methanol and air at atmospheric pressure. Initial screening of membranes was carried out using a "sandwich" membrane electrode assembly (MEA) design, where a polyphosphazene film was inserted between two half-MEAs made with Nafion 112. MEAs were also prepared by hot-pressing catalyst electrodes directly onto SPOP-PBI blended films. Comparable current-voltage data were obtained with the two MEA configurations. Membrane performance in a DMFC was dependent on the blend composition (ion-exchange capacity, IEC, of the SPOP and wt % of added PBI). For an 82 μm thick membrane composed of IEC SPOP with 3 wt % PBI, the maximum power density was ( vs. with Nafion 117), while the methanol crossover was 2.6 times lower than that with Nafion 117.
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- Findingown data
For the 82 μm thick membrane composed of 1.2 mmol/g IEC SPOP with 3 wt % PBI, methanol crossover was 2.6 times lower than that with Nafion 117.
“while the methanol crossover was 2.6 times lower than that with Nafion 117.”
Quote in the paperSubstantial claim - Findingown data
Membrane performance in a DMFC was dependent on the blend composition, specifically the ion-exchange capacity of the SPOP and the wt % of added PBI.
“Membrane performance in a DMFC was dependent on the blend composition ͑ion-exchange capacity, IEC, of the SPOP and wt % of added PBI͒.”
Quote in the paperSubstantial claim - Findingown data
Comparable current-voltage data were obtained with the two MEA configurations.
“Comparable current-voltage data were obtained with the two MEA configurations.”
Quote in the paperNot a substantial claim - Findingown data
At room temperature, a pure 1.4 mmol/g SPOP film sorbed approximately 0.75 g of water per 1 g of dry polymer.
“At room temperature, a pure 1.4 mmol/g SPOP film sorbed Ϸ0.75 g of water per 1 g of the dry polymer”
Quote in the paperNot a substantial claim - Findingown data
The resulting membranes had an equilibrium water swelling from 18-75%.
“Depending on the SPOP ion-exchange capacity and the amount of added PBI, the resulting membranes had a room temperature proton conductivity in the range 0.005-0.08S/cm, an equilibrium water swelling from 18-75% and a room-temperature methanol permeability ͑60°C, 1.0 M methanol͒ that ranged from 1.0 ϫ 10 -7 to 2.0 ϫ 10 -6 cm 2 /s.”
Quote in the paperSubstantial claim
- Findingown data
The swelling of a SPOP14-PBI05 membrane in 1.0 M methanol at 60°C increased slowly with time from an initial value of 59% and eventually stabilized at 125% near the end of the 408 h experiment.
“It was found that the swelling increased slowly with time ͑from an initial value of 59%͒ and eventually stabilized at 125% near the end of the experiment.”
Quote in the paperSubstantial claim - Findingown data
During the 408 h soak, the proton conductivity of the SPOP14-PBI05 membrane remained unchanged at 0.04 S/cm.
“During this time, the proton conductivity remained unchanged ͑at 0.04 S/cm͒.”
Quote in the paperSubstantial claim - Findingown data
DMFC performance with the 1.2 mmol/g IEC SPOP membrane with 3 wt % PBI was essentially identical to that with Nafion 117.
“DMFC performance with the 1.2 mmol/g IEC SPOP membrane with 3 wt % PBI was essentially identical to that with Nafion 117, but the methanol crossover was 2.5 times lower than that of Nafion.”
Quote in the paperSubstantial claim - Findingown data
Differences in membrane resistance, associated with membrane thickness, did not affect the DMFC power output for the Nafion 112 sandwich and single Nafion 117 MEAs.
“Differences in membrane resistance, associated with membrane thickness, did not affect the DMFC power output for the Nafion 112 sandwich and single Nafion 117 MEAs.”
Quote in the paperNot a substantial claim - Findingown data
The selectivity with respect to Nafion 117 was 2.2 and 2.5 for 1.4 mmol/g SPOP membranes containing 5% PBI and 8% PBI, respectively.
“respect to Nafion 117͒ was found to be 2.2 and 2.5 for a 1.4 mmol/g SPOP membranes containing 5% PBI and 8% PBI, respectively.”
Quote in the paperSubstantial claim - Findingnone given
Comparable current-voltage DMFC characteristics were obtained with the two MEA configurations.
“Comparable current-voltage DMFC characteristics were obtained with the two MEA configurations.”
Quote in the paperSubstantial claim - Findingown data
Conductivity decreased with PBI content at a given temperature.
“a decrease in conductivity with PBI content at a given temperature”
Quote in the paperSubstantial claim - Findingown data
The maximum DMFC power density for a SPOP12-PBI03 membrane was just below that for Nafion 117, 89 mW/cm2 vs. 96 mW/cm2.
“As expected, the maximum DMFC power density for a SPOP12-PBI03 membrane was just below that for Nafion 117, 89 mW/cm 2 vs. 96 mW/cm 2 .”
Quote in the paperSubstantial claim - Findingown data
The fuel cell performance curves for the SPOP-PBI membranes in Fig. 10 are ordered according to the PBI content of the inner SPOP-PBI film.
“The fuel cell performance curves for the SPOP-PBI membranes in Fig. 10 are ordered according to the PBI content of the inner SPOP-PBI film, indicating that membrane resistance was the primary factor in determining the shape of the current/voltage plots ͑i.e., the slope of the plots in the IR regime͒.”
Quote in the paperSubstantial claim - Findingnone given
Methanol crossover remained unchanged for the entire 100 h.
“Methanol crossover remained unchanged for the entire 100 h.”
Quote in the paperSubstantial claim - Findingown data
The DMFC with membranes containing 3 or 5% PBI generated nearly as much power as that with a Nafion 117 membrane MEA.
“The DMFC with membranes containing 3 or 5% PBI generated nearly as much power as that with a Nafion 117 membrane MEA.”
Quote in the paperSubstantial claim - Findingreasoning
The difference between experimental and calculated IEC increased slightly with increasing PBI content.
“The difference between experimental and calculated IEC increased slightly with increasing PBI content.”
Quote in the paperNot a substantial claim - Findingnone given
After the regeneration step, the cell voltage once again began to decrease.
“After this regeneration step, however, the cell voltage once again began to decrease.”
Quote in the paperNot a substantial claim - Findingown data
The water sorption of pure SPOP is twice that for Nafion 117.
“which is twice that for Nafion 117.”
Quote in the paperNot a substantial claim - Findingown data
Based on conductivity and permeability data collected at 60°C, the relative selectivity with respect to Nafion 117 was 2.2 for a 1.4 mmol/g SPOP membrane containing 5% PBI.
“the relative selectivity ͑with respect to Nafion 117͒ was found to be 2.2 and 2.5 for a 1.4 mmol/g SPOP membranes containing 5% PBI and 8% PBI, respectively.”
Quote in the paperSubstantial claim - Findingown data
During the 100 h DMFC test at 0.10 A/cm2, the cell voltage decreased slowly at a rate of ~0.8 mV/h (from an initial value of 0.39 to 0.31 V after 100 h).
“During the experiment, the cell voltage decreased slowly at a rate of ϳ0.8 mV/h ͑from an initial value of 0.39 to 0.31 V after 100 h͒.”
Quote in the paperSubstantial claim - Findingown data
The methanol crossover with the 1.2 mmol/g IEC SPOP membrane with 3 wt % PBI was 2.5 times lower than that of Nafion.
“DMFC performance with the 1.2 mmol/g IEC SPOP membrane with 3 wt % PBI was essentially identical to that with Nafion 117, but the methanol crossover was 2.5 times lower than that of Nafion.”
Quote in the paperSubstantial claim - Findingreasoning
A linear decrease of IEC with PBI content was found.
“As expected, a linear decrease of IEC with PBI content was found”
Quote in the paperSubstantial claim - Findingnone given
Conductivity increased with temperature at a given PBI content.
“an increase in conductivity with temperature at a given PBI content”
Quote in the paperNot a substantial claim - Findingown data
Methanol permeabilities from the fuel cell tests matched well those measured in the methanol diffusion cell.
“Methanol permeabilities from the fuel cell tests matched well those measured in the methanol diffusion cell, as shown in Fig. 11.”
Quote in the paperNot a substantial claim - Findingnone given
The initial cell voltage could be fully recovered by lowering the temperature to 25°C and washing the membrane with deionized water for 2 h.
“The initial cell voltage could be fully recovered by lowering the temperature to 25°C and washing the membrane with deionized water for 2 h ͑either by removing the MEA from the fuel cell test fixture or by an in situ procedure where the methanol feed solution is replaced by roomtemperature water͒.”
Quote in the paperNot a substantial claim - Findingnone given
SPOP-PBI membranes equilibrated in 1.0 M H2SO4 and then deionized water at 60°C swelled more than the same films at 25°C.
“SPOP-PBI membranes that were equilibrated in 1.0 M H 2 SO 4 and then deionized water at 60°C, swelled more than the same films at 25°C.”
Quote in the paperNot a substantial claim - Findingnone given
When PBI concentration was increased to 12 wt %, the water content dropped to 15%.
“When the PBI concentration was increased to 12 wt %, the water content dropped to 15%”
Quote in the paperSubstantial claim - Findingown data
The conductivity was 0.005 S/cm when the film contained 12% PBI.
“with a lower value of 0.005 S/cm when the film contained 12% PBI.”
Quote in the paperSubstantial claim - Findingown data
The most visible drop in performance occurred for membranes containing 10 and 12% PBI.
“The most visible drop in performance occurred for membranes containing 10 and 12% PBI.”
Quote in the paperNot a substantial claim - Findingown data
Experimentally determined IECs fell slightly below their theoretical counterpart.
“Experimentally determined IECs fell slightly below their theoretical counterpart, as shown in Fig. 6”
Quote in the paperNot a substantial claim - Findingown data
Upon further constant current operation, the voltage again began to slowly decrease.
“Upon further constant current operation, the voltage again began to slowly decrease.”
Quote in the paperSubstantial claim - Findingown data
The methanol permeability of a pure 1.4 mmol/g SPOP film at 60°C was 2.0 × 10−6 cm2/s.
“The permeability decreased from 2.0 ϫ 10 -6 cm 2 /s for a pure 1.4 mmol/g SPOP film to”
Quote in the paperSubstantial claim - Findingnone given
The yields of the sulfonation reaction were quantitative, i.e., greater than 95%.
“the yields of the sulfonation reaction were quantitative ͑i.e., Ͼ95%͒.”
Quote in the paperNot a substantial claim - Findingown data
During a 100 h DMFC test at 0.10 A/cm2, the cell voltage decreased by ~0.8 mV/h.
“During a 100 h DMFC test at 0.10 A/cm 2 , the cell voltage decreased by ϳ0.8 mV/h.”
Quote in the paperSubstantial claim - Findingreasoning
The films retained the increased swelling when they were re-equilibrated in room temperature water.
“The films retained the increased swelling when they were re-equilibrated in room temperature water.”
Quote in the paperNot a substantial claim - Findingown data
The resulting membranes had a room temperature proton conductivity in the range 0.005-0.08 S/cm.
“Depending on the SPOP ion-exchange capacity and the amount of added PBI, the resulting membranes had a room temperature proton conductivity in the range 0.005-0.08S/cm, an equilibrium water swelling from 18-75% and a room-temperature methanol permeability ͑60°C, 1.0 M methanol͒ that ranged from 1.0 ϫ 10 -7 to 2.0 ϫ 10 -6 cm 2 /s.”
Quote in the paperSubstantial claim - Findingown data
Based on conductivity and permeability data collected at 60°C, the relative selectivity with respect to Nafion 117 was 2.5 for a 1.4 mmol/g SPOP membrane containing 8% PBI.
“the relative selectivity ͑with respect to Nafion 117͒ was found to be 2.2 and 2.5 for a 1.4 mmol/g SPOP membranes containing 5% PBI and 8% PBI, respectively.”
Quote in the paperSubstantial claim - Findingnone given
There was no obvious indication of polymer degradation during sulfonation.
“There was no obvious indication of polymer degradation during sulfonation”
Quote in the paperNot a substantial claim - Findingown data
The ion-exchange capacity of the polyphosphazene increased from 0.95 to 1.35 mmol/g as the sulfonation time increased from 95 to 120 min.
“the ion-exchange capacity of the polyphosphazene increased from 0.95 to 1.35 mmol/g as the sulfonation time increased from 95 to 120 min.”
Quote in the paperNot a substantial claim - Findingown data
The resulting membranes had a room-temperature methanol permeability (60°C, 1.0 M methanol) that ranged from 1.0 × 10^-7 to 2.0 × 10^-6 cm2/s.
“Depending on the SPOP ion-exchange capacity and the amount of added PBI, the resulting membranes had a room temperature proton conductivity in the range 0.005-0.08S/cm, an equilibrium water swelling from 18-75% and a room-temperature methanol permeability ͑60°C, 1.0 M methanol͒ that ranged from 1.0 ϫ 10 -7 to 2.0 ϫ 10 -6 cm 2 /s.”
Quote in the paperSubstantial claim - Findingown data
At the same time, the cell resistance, as measured by the current interrupt method, slowly increased.
“At the same time, the cell resistance, as measured by the current interrupt method, slowly increased.”
Quote in the paperNot a substantial claim - Findingown data
The relative methanol crossover (relative to Nafion 117) decreased from 0.78 for the MEA sandwich containing a SPOP membrane with 3% PBI to 0.06 for the MEA with a 12% PBI blend.
“The relative crossover ͑relative to that of Nafion 117͒ decreased from 0.78 for the MEA sandwich containing a SPOP membrane with 3% PBI to 0.06 for the MEA with a 12% PBI blend.”
Quote in the paperSubstantial claim - Findingown data
Permeabilities of the SPOP-PBI films were 3-20 times lower than that in Nafion 117 at 60°C.
“Permeabilities of the SPOP-PBI films were 3-20 times lower than that in Nafion 117 at 60°C.”
Quote in the paperSubstantial claim - Premisenone given
In modified Nafion membranes, there was always a significant loss in proton conductivity when methanol permeability was reduced.
“Unfortunately, there was always a significant loss in proton conductivity when the methanol permeability was reduced.”
Quote in the paperSubstantial claim0 of 3 sources checked - Premisecitation
A similar conductivity/methanol crossover correlation has been observed with new polymeric materials, where protonic conductivity decreases as the methanol barrier property of the film improves.
“A similar conductivity/methanol crossover correlation has been observed with these polymers, where the protonic conductivity decreases as the methanol barrier property of the film improves.”
Quote in the paperNot a substantial claim0 of 3 sources checked - Interpretationnone given
The increase in swelling is indicative of the relaxation of the polyphosphazene structure upon an osmotic stress at elevated temperature.
“The increase in swelling is indicative of the relaxation of the polyphosphazene structure upon an osmotic stress at elevated temperature.”
Quote in the paperSubstantial claim - Interpretationreasoning
A water content of 15% is probably the lower swelling limit for practical applications.
“which is probably the lower swelling limit for practical applications”
Quote in the paperSubstantial claim- Rests on an assumption: Further reduction in water content below 15% shifts the system below the percolation transition, resulting in negligible proton conduction.
- Interpretationown data
Membrane resistance was the primary factor in determining the shape of the current/voltage plots (i.e., the slope of the plots in the IR regime) for the SPOP-PBI membranes.
“The fuel cell performance curves for the SPOP-PBI membranes in Fig. 10 are ordered according to the PBI content of the inner SPOP-PBI film, indicating that membrane resistance was the primary factor in determining the shape of the current/voltage plots ͑i.e., the slope of the plots in the IR regime͒.”
Quote in the paperSubstantial claim - Interpretationreasoning
The strong decrease in swelling with increasing PBI concentration at relatively low PBI contents can be regarded as proof that the SPOP component of the blend is being cross-linked.
“The strong decrease in swelling with increasing PBI concentration at the relatively low PBI contents, can be regarded as proof that the SPOP component of the blend is being cross-linked.”
Quote in the paperSubstantial claim - Interpretationreasoning
The polymer relaxation time was extremely slow due to the relatively high flexibility and hydrophilicity of the polyphosphazene network.
“It was concluded that the polymer relaxation time was extremely slow due to the relatively high flexibility and hydrophilicity of the polyphosphazene network.”
Quote in the paperSubstantial claim - Interpretationnone given
The sandwich-type MEA circumvents the need to identify the proper electrode catalyst/binder composition and hot-pressing conditions.
“The sandwich-type MEA is attractive for preliminary fuel cell screening of new membrane materials; the use of such a configuration circumvents the need to identify the proper electrode catalyst/binder composition and hotpressing conditions.”
Quote in the paperSubstantial claim- Rests on an assumption: MEA failures often occur due to poor electrode contact and/or insufficient catalyst utilization rather than poor membrane performance.
- Interpretationown data
Some imidazole groups in PBI did not react with the acid groups of SPOP.
“indicating that some imidazole groups in PBI did not react with the acid groups of SPOP.”
Quote in the paperSubstantial claim - Interpretationreasoning
Protons involved in crosslink formation are immobilized by interaction with the basic sites of PBI and are no longer available for charge transport.
“the cross-linking mechanism, where protons involved in crosslink formation are immobilized by interaction with the basic sites of PBI and therefore are no longer available for charge transport.”
Quote in the paperSubstantial claim - Interpretationown data
The higher methanol crossover for the Nafion 112 sandwich compared to Nafion 117 is due to the difference in total membrane thickness.
“The higher crossover for the Nafion 112 sandwich as compared to Nafion 117 ͑7 mils dry thickness͒ is due to a difference in total membrane thickness ͑3 Nafion 112 films at 2 mils dry thickness each vs. one 7 mil thick film for Nafion 117͒.”
Quote in the paperNot a substantial claim - Interpretationown data
The voltage loss has been associated with a growing contact resistance between the SPOP-PBI membrane and the Nafion binder in the electrodes, due to the difference in swelling of the two polymers and the slow upward drift of the SPOP-PBI swelling in 1.0 M methanol.
“At the present time, the voltage loss has been associated with a growing contact resistance between the SPOP-PBI membrane and the Nafion binder in the electrodes, due to the difference in swelling of the two polymers and the slow upward drift of the SPOP-PBI swelling in 1.0 M methanol.”
Quote in the paperSubstantial claim - Interpretationreasoning
The drop in conductivity is partly due to a dilution effect, where increasing weak protonic conductor PBI in a mixture with good conductor SPOP leads to decreased effective conductivity.
“a simple dilution effect, where an increase in weak protonic conductor ͑PBI͒ content in a mixture with a good conductor ͑SPOP͒ will generally lead to a decrease in the effective conductivity of the blend”
Quote in the paperSubstantial claim - Interpretationown data
The constant proton conductivity showed that there was no dissociation of the sulfonate-imidazole crosslinks.
“The constant conductivity showed that there was no dissociation of the sulfonate-imidazole crosslinks ͑as shown in Fig. 6, conductivity is sensitive to the number of acid-base cross-links͒.”
Quote in the paperSubstantial claim - Interpretationreasoning
Reduced imidazole group utilization at higher PBI loadings is consistent with the relative stiffness of the PBI polymer chains and the observed increase in viscosity of the membrane casting solution with PBI content.
“The reduced imidazole group utilization at higher PBI loadings is consistent with the relative stiffness of the PBI polymer chains and the observed increase in viscosity of the membrane casting solution with PBI content.”
Quote in the paperNot a substantial claim - Interpretationnone given
The lower methanol crossovers in the direct attachment MEAs, as compared to the sandwich design data in Fig. 10 for the same membrane composition, are due to differences in membrane thickness.
“The lower methanol crossovers in the direct attachment MEAs, as compared to the sandwich design data in Fig. 10 ͑for the same membrane composition͒ are due to differences in membrane thickness.”
Quote in the paperNot a substantial claim - Interpretationreasoning
The linear decrease in IEC with PBI content is because sulfonic acid protons of SPOP were consumed when acid-base cross-links formed in the SPOP-PBI blends.
“because sulfonic acid protons of SPOP were consumed when acid-base cross-links formed in the SPOP-PBI blends.”
Quote in the paperSubstantial claim - Interpretationown data
These polarization plots suggest that membrane resistance is not an issue for blended films containing 3 and 5 wt % PBI.
“These polarization plots suggest that membrane resistance is not an issue for blended films containing 3 and 5 wt % PBI.”
Quote in the paperSubstantial claim
- May combine two claims. 16
- Classified as probably not a substantial claim. 5
- The quote only partly states this claim. 2
May combine two claims.
Findingown dataFor an 82 μm thick membrane composed of 1.2 mmol/g IEC SPOP with 3 wt % PBI, the maximum power density was 89 mW/cm2, compared with 96 mW/cm2 for Nafion 117.
“For an 82 µm thick membrane composed of 1.2 mmol/g IEC SPOP with 3 wt % PBI, the maximum power density was 89 mW/cm 2 ͑vs.96 mW/cm 2 with Nafion 117͒”
Quote in the paperSubstantial claimMay combine two claims.
Findingown dataA slow, upward drift in membrane swelling, with no change in proton conductivity, was observed when the blended films were soaked in 1.0 M methanol at 60°C for 17 days.
“A slow, upward drift in membrane swelling, with no change in proton conductivity, was observed when the blended films were soaked in 1.0 M methanol at 60°C for 17 days.”
Quote in the paperSubstantial claimMay combine two claims.
Findingown dataThe voltage loss was reversible; by exposing the MEA to room temperature water, there was complete recovery of MEA performance.
“The voltage loss was reversible; by exposing the MEA to room temperature water, there was complete recovery of MEA performance.”
Quote in the paperSubstantial claimMay combine two claims.
Findingown dataThe IR-corrected polarization curves for a SPOP-PBI membrane containing 3 wt % PBI fell above that for Nafion 117, while the performance curves with membranes SPOP14-PBI05 and SPOP12-PBI05, and SPOP14-PBI12 were slightly lower than the Nafion 117 curve.
“The resulting current density/voltage polarization curves for a SPOP-PBI membrane containing 3 wt % PBI fell above that for Nafion 117, while the performance curves with membranes SPOP14-PBI05 and SPOP12-PBI05, and SPOP14-PBI12 were slightly lower than the Nafion 117 curve.”
Quote in the paperSubstantial claimMay combine two claims.
Findingown dataAlthough the thicknesses of the blended SPOP-PBI membranes were less than half that of Nafion 117, the methanol crossover was very low.
“Although the thicknesses of the blended SPOP-PBI membranes were less than half that of Nafion 117, the methanol crossover was very low.”
Quote in the paperSubstantial claimMay combine two claims.
Findingown dataFor an MEA prepared from 1.4 mmol/g SPOP with 5 wt % PBI, where the methanol crossover is three times lower than that of Nafion 117, the maximum power density remained high, at 78 mW/cm2.
“For an MEA prepared from 1.4 mmol/g SPOP, with 5 wt % PBI, where the methanol crossover is three times lower than that of Nafion 117, the maximum power density remained high, at 78 mW/cm 2 .”
Quote in the paperSubstantial claimMay combine two claims.
Findingown dataThe open circuit voltage with the SPOP-PBI membranes was high (>0.8 V vs. 0.63 V with Nafion 117), providing additional proof of low methanol crossover.
“Additional proof of low methanol crossover was the high open circuit voltage with the SPOP-PBI membranes ͑Ͼ0.8 V vs. 0.63 V with Nafion 117͒.”
Quote in the paperSubstantial claimMay combine two claims.
PremisecitationSulfonated poly(alkylphenoxy)phosphazenes possess acceptably high proton conductivity, crosslinkability, and low methanol permeability.
“who showed that sulfonated poly͑alkylphe-noxy͒phosphazenes possess an acceptably high proton conductivity, crosslinkability, and low methanol permeability.”
Quote in the paperSubstantial claim0 of 3 sources checkedProbably not a substantial claim: may not pass S1 (asserted), S3 (load-bearing), S4 (based). May combine two claims. The quote only partly states this claim.
Premiseown dataMembranes from UV-cross-linked blends of sulfonated poly[bis(3-methylphenoxy)phosphazene] and polyacrylonitrile used in a DMFC had reduced methanol crossover but lower current-voltage performance than Nafion 117.
“Although the methanol crossover was reduced, the current-voltage performance was lower than that obtained with Nafion 117.”
Quote in the paperNot a substantial claim0 of 3 sources checkedProbably not a substantial claim: may not pass S3 (load-bearing).
PremisecitationThe relative selectivity parameter for DMFC membranes is generally between 1.0 and 2.0, even though methanol permeability may be very low.
“In general, this selectivity parameter is between 1.0 and 2.0, even though the methanol permeability may be very low ͑see, for example, Ref. 22͒.”
Quote in the paperNot a substantial claim0 of 1 sources checked- cites [22] P. Zelenay ,Direct Methanol Fuel Cells, Los Alamos National Laboratory (2004).
Not checked in the free run.
Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.
PremisecitationAllcock et al. synthesized polyphosphazenes with phosphonic or sulfonimide groups, where the former exhibited low methanol permeability, although no DMFC data were collected.
“Allcock et al. [26][27][28] synthesized polyphosphazenes with phosphonic or sulfonimide groups, where the former exhibited low methanol permeability, although no DMFC data were collected.”
Quote in the paperNot a substantial claim0 of 3 sources checkedProbably not a substantial claim: may not pass S3 (load-bearing).
Study design and conductreasoningAs a check on the experimental results, the effective membrane IEC was calculated based on the IEC and amount of SPOP in the blend, the amount of added PBI, and the theoretical protonation capacity of PBI.
“As a check on the experimental results, the effective membrane IEC was calculated, based on the IEC and amount of SPOP in the blend, the amount of added PBI, and the theoretical protonation capacity of PBI ͑estimated to be 6.5 mmol/g͒.”
Quote in the paperNot a substantial claimMay combine two claims.
InterpretationreasoningThese selectivities suggest that methanol crossover in a SPOP-PBI MEA will be at least two times lower than that in Nafion 117, with current-voltage characteristics similar to that of Nafion 117 MEA, when the blended films are made sufficiently thin so that their protonic resistance is similar to that of Nafion 117.
“These selectivities suggest that methanol crossover in a SPOP-PBI MEA will be at least two times lower than that in Nafion 117, with current-voltage characteristics similar to that of Nafion 117 MEA, when the blended films are made sufficiently thin so that their protonic resistance is similar to that of Nafion 117.”
Quote in the paperSubstantial claimMay combine two claims.
Interpretationown dataThe highly blocking film (1.4 mmol/g SPOP with 12 wt % PBI) had a high sheet resistance which resulted in low power output during fuel cell operation.
“Unfortunately, this highly blocking film had a high sheet resistance which resulted in low power output during fuel cell operation.”
Quote in the paperSubstantial claimMay combine two claims.
InterpretationreasoningAddition of PBI causes cross-linking of SPOP, which results in reduced water sorption.
“addition of PBI causes cross-linking of the SPOP, which in turn results in reduced water sorption ͑equilibrium swelling͒”
Quote in the paperSubstantial claimMay combine two claims.
Study design and conductown dataThe i-V curves for the Nafion 117 single-membrane MEA and the Nafion 112 sandwich MEA overlap, indicating proper MEA fabrication and fuel cell operation.
“The i-V curves for these two MEA configurations show good fuel cell performance and overlap indicating proper MEA fabrication and fuel cell operation.”
Quote in the paperNot a substantial claimMay combine two claims.
PremisecitationProton transfer between sulfonic acid sites and polymeric basic moieties in acid-base membrane blends leads to cross-links that increase osmotic stability (lower solvent swelling) and reduce membrane brittleness upon drying, compared to uncross-linked or covalently crosslinked sulfonic acid polymers.
“Proton transfer ͑partial or complete͒ between sulfonic acid sites and polymeric basic moieties in the blend lead to the formation of cross-links which increased the osmotic stability ͑lower solvent swelling͒ of the resultant membrane and also reduced membrane brittleness upon drying, as compared to uncross-linked or covalently crosslinked sulfonic acid polymers.”
Quote in the paperSubstantial claim0 of 3 sources checkedProbably not a substantial claim: may not pass S3 (load-bearing).
Study design and conductnone givenPrior to measurements, the CO2 sensor was calibrated with reference CO2/N2 gas mixtures containing 400-5000 ppm of CO2.
“Prior to measurements, the sensor was calibrated with reference CO 2 /N 2 gas mixtures containing 400-5000 ppm of CO 2 .”
Quote in the paperNot a substantial claimMay combine two claims. The quote only partly states this claim.
Interpretationown dataNo degradation or dissolution of the polymer occurred during the lifetime soak test.
“Thus, it can be concluded that no degradation of the membrane material was observed during the lifetime soak test.”
Quote in the paperSubstantial claim- Rests on an assumption: The swelling increase observed in soak tests will be insignificant under a compressive force in a fuel cell test fixture.
The paper relies on this without support.
Further reduction in water content below 15% shifts the system below the percolation transition, resulting in negligible proton conduction.
“because any further reduction in water content shifts the system below the percolation transition ͑resulting in negligible proton conduction͒.”
The paper relies on this without support.
MEA failures often occur due to poor electrode contact and/or insufficient catalyst utilization rather than poor membrane performance.
“Often, an MEA will fail, not because the membrane performs poorly, but rather due to poor contact of the electrodes to the membrane and/or insufficient catalyst utilization due to problems associated with the catalyst binder and electrode/ membrane interfacial microstructure.”
The paper relies on this without support.
The swelling increase observed in soak tests will be insignificant under a compressive force in a fuel cell test fixture.
“It is expected that this effect will be insignificant under a compressive force in a fuel cell test fixture.”
Claims other papers make about this one
Each is checked against this paper’s own text: does it say what the citing paper says it does?
Blend membranes' reduced methanol crossover stems from their lower swelling and IEC relative to plain SPEEK, which arise from ionic cross-linking via acid-base interaction.
“Also, as reported for other acid-base blend membranes, the lower methanol crossover in the blend membranes is due to the lower swelling and lower IEC compared to the plain SPEEK membrane as a result of the ionic cross-linking through acid-base interaction in the blend membranes [31,32].”
From Acid–base blend membranes consisting of sulfonated poly(ether ether ketone) and 5-amino-benzotriazole tethered polysulfone for DMFC (2010) · cites this paper as [31]
The Results and Discussion report that acid–base cross-links in SPOP–PBI blends reduce effective IEC, while p. A894 reports reduced swelling and methanol permeability as PBI content increases. The paper studies SPOP–PBI, not a comparison with plain SPEEK, so it does not support that specific comparator or establish the stated cause of a SPEEK blend’s lower crossover. (LLM, conf=0.86)
Experimental — accuracy not yet measuredDespite lower IEC values caused by acid-base interactions, SPEEK/PSf-BTraz membranes conduct protons better than plain SPEEK.
“Compared to some blend membrane systems based on acid-base interactions that have been investigated in the literature [18,19,31,32], the SPEEK/PSf-BTraz blend membranes presented here show higher proton conductivity than plain SPEEK membrane despite a decrease in the IEC values due to acid-base interactions.”
From Acid–base blend membranes consisting of sulfonated poly(ether ether ketone) and 5-amino-benzotriazole tethered polysulfone for DMFC (2010) · cites this paper as [31]
Self-check
Percentages, sums and reported differences re-computed from the paper’s own numbers.
Each contradiction between two passages listed here was confirmed by an independent check.
Four blended membranes are listed for a purported set of five
MinorThe text says Figure 12 shows five different blended membranes, but its caption lists only four SPOP-PBI membranes, plus a Nafion reference.
“Representativei-V curves for five different blended membranes with direct electrode attachment are shown in Fig. 12, along with a reference plot of a Nafion 117 based MEA.”
“b Nafion 117 ͑reference͒; ᭺ SPOP12-PBI03, 82 µm thick; ᮀ SPOP14-PBI05, 115 µm thick; ᭡ SPOP12-PBI05, 120 µm thick; छ SPOP14-PBI12, 95 µm thick.”
The stated PBI range omits the membrane with the highest reported power
MinorThe conclusion gives a PBI-content range of 5-12% for the hot-pressed MEAs, but the reported 89 mW/cm2 maximum belongs to a membrane containing 3 wt % PBI.
“Depending on the ion-exchange capacity of the SPOP ͑either 1.2 or 1.4 mmol/g͒ and the PBI content of the membrane ͑which ranged from 5 to 12%͒, the maximum DMFC power density with hot-pressed MEAs ranged from 23 to 89 mW/cm 2”
“For an 82 µm thick membrane composed of 1.2 mmol/g IEC SPOP with 3 wt % PBI, the maximum power density was 89 mW/cm 2”
The reported minimum water swelling differs
MinorThe conclusion gives 18% as the lower end of the swelling range, whereas the results report 15% for a membrane containing 12 wt % PBI.
“an equilibrium water swelling from 18-75%”
“When the PBI concentration was increased to 12 wt %, the water content dropped to 15%”
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Direct methanol fuel cell membranes from Nafion-polybenzimidazole blends
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- Authors
- Wycisk, R., Lee, J. K., & Pintauro, P. N.
- Affiliations
- Case Western Reserve University (US)
- Venue
- Journal of The Electrochemical Society
- Publisher
- The Electrochemical Society
- Published
- 2005
- Volume
- 152
- Issue
- 5
- Pages
- A892
- ISSN
- 0013-4651 (ISSN-L)
- OpenAlex
- W2040079950
- Cited by
- 83
- References
- 35
- Citations by year
- 2024: 1 · 2022: 1 · 2021: 2 · 2020: 2 · 2018: 1 · 2017: 3 · 2016: 4 · 2015: 8 · 2014: 9 · 2013: 4 · 2012: 3
- FWCI
- 7.91
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Journal of The Electrochemical Society (publishedVersion)
- Funders
- Office of Research and Development
- Case Western Reserve University
- Army Research Office
- Topics
- Physical Sciences › Engineering › Electrical and Electronic Engineering › Fuel Cells and Related Materials
- Physical Sciences › Engineering › Mechanical Engineering › Membrane Separation and Gas Transport
- Physical Sciences › Materials Science › Materials Chemistry › Advancements in Solid Oxide Fuel Cells
- Keywords
- polybenzimidazole, proton-conducting membranes, direct methanol fuel cells, membrane electrode assembly, methanol permeability, methanol crossover, ion exchange capacity, Nafion 117 comparison, water swelling, proton conductivity
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