Comparison between Nafion® and a Nafion® Zirconium Phosphate Nano‐Composite in Fuel Cell Applications
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Abstract A comparative investigation of the electrical, mechanical, and chemical behaviour of zirconium phosphate‐Nafion® composite membranes and Nafion® by means of ex‐situ measurements, as well as with fuel cell operation, reveals a slight reduction of ionic conductivity, a significant improvement of mechanical stability, and increased water retention for the composite materials. The overall efficiency at 130 °C is increased during direct methanol fuel cell (DMFC) operation because the reduction in the ionic conductivity is overcompensated for by the decrease in methanol crossover. With H 2 as the fuel, the slight reduction in overall efficiency corresponds to the decrease in ionic conductivity. The dimensional stability of the membrane and the membrane electrode assembly (MEA) is significantly improved for operating temperatures above 100 °C. A model for the microstructure‐property relation for PFSA‐Zr(HPO 4 ) 2 · n H 2 O composite membranes is presented, based on the experimental results from membranes with varying filler contents and distributions, obtained through different synthesis routes. It is aimed at the improvement of water distribution in the membrane upon fuel cell operation.Keywords:
Nafion
Membrane electrode assembly
Zirconium phosphate
Chemical Stability
Abstract Gels of exfoliated α‐zirconium phosphate (ZrP exf ) in dimethylformamide (DMF) were used to prepare Nafion/ZrP exf composite membranes with filler loadings up to 7 wt.‐% by casting mixtures of Nafion 1100 solutions in DMF and suitable amounts of 2 wt.‐% ZrP gels in DMF. TEM pictures showed that the ZrP exf particles had aspect ratio of at least 20. All samples were characterised by methanol permeability ( P ) and through‐plane (σ thp ) and in‐plane (σ inp ) conductivity measurements at 40 °C and 100% RH. The methanol permeability of Nafion membranes containing in situ grown ZrP particles with low aspect ratio (Nafion/ZrP isg ) was also determined. The methanol permeability and the swelling behaviour of the composite membranes turned out to be strongly dependent on the filler morphology. As a general trend, both permeability and swelling decreased according to the sequence: Nafion/ZrP isg > Nafion > Nafion/ZrP exf . The maximum selectivity (σ thp /P = 1.4 × 10 5 S cm –3 s) was found for the membrane filled with 1 wt.‐% ZrP exf : this value is seven times higher than that of Nafion. For the Nafion/ZrP exf membranes, the ratio σ inp /σ thp increases with the filler loading, thus indicating that the preferred orientation of the ZrP sheets is parallel to the membrane surface.
Nafion
Zirconium phosphate
Dimethyl formamide
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Nafion
Ionomer
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Abstract Nafion–zirconium phosphate (ZrP) composite membranes, containing 20 to 40 wt.‐% ZrP were treated with aqueous solutions of meta‐sulphophenylphosphonic acid (H 2 SPP) in order to functionalise the filler particles with strongly acidic sulphonic groups. The functionalised samples (Nafion/ZrSPP) were characterised by 31 P MAS NMR, water uptake determinations, stress–strain mechanical tests and conductivity measurements. The Nafion/ZrSPP membranes are more hydrophilic than Nafion 117 and stiffer than the parent Nafion/ZrP membranes: at room temperature, the elastic modulus of the membranes with 20 and 40 wt.‐% ZrP increases from 191 and 329 N mm –2 to 342 and 470 N mm –2 , respectively, after functionalisation. At 100 °C and in the RH range of 30–90% the conductivity of the Nafion/ZrSPP membranes decreases with the increase in the filler loading, being however always higher than that of the parent Nafion/ZrP membranes and nearly coincident with that of Nafion 117. Conductivity measurements as a function of temperature in the range of 80–150 °C showed that, at 90% RH, the conductivity of the Nafion/ZrSPP membranes is stable up to 140 °C thus indicating a better dimensional stability of the composite membrane in comparison with neat Nafion 117.
Nafion
Zirconium phosphate
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Membrane electrode assembly
Nafion
Methanol fuel
Power density
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