Proton conductivity and diffusion study of molten phosphonic acid H3PO3

Schuster, Michael; Kreuer, Klaus‐Dieter; Steininger, Hanna; Maier, Joachim

doi:10.1016/j.ssi.2008.03.030

Cited by 64 publications

(58 citation statements)

References 35 publications

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“…Haven ratios for H 3 PO 4 have been reported to vary between 1.5 and 1.7, [5] and values for H 3 PO 3 vary between 2.5 and 3.0. [24] These values are reasonably close to those for the fluoroalkylated phosphorous-based acids studied herein. Significantly, in all cases, the ratios for the phosphonic acids were lower than those for the phosphinic acids, which suggests that the degree of dissociation of the phosphonic acids is probably higher than that for the phosphinic acids.…”

Section: Nernst-einstein Relation and Haven Ratiosupporting

confidence: 85%

Perfluoroalkyl Phosphonic and Phosphinic Acids as Proton Conductors for Anhydrous Proton‐Exchange Membranes

et al. 2010

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A study of proton-transport rates and mechanisms under anhydrous conditions using a series of acid model compounds, analogous to comb-branch perfluorinated ionomers functionalized with phosphonic, phosphinic, sulfonic, and carboxylic acid protogenic groups, is reported. Model compounds are characterized with respect to proton conductivity, viscosity, proton, and anion (conjugate base) self-diffusion coefficients, and Hammett acidity. The highest conductivities, and also the highest viscosities, are observed for the phosphonic and phosphinic acid model compounds. Arrhenius analysis of conductivity and viscosity for these two acids reveals much lower activation energies for ion transport than for viscous flow. Additionally, the proton self-diffusion coefficients are much higher than the conjugate-base self-diffusion coefficients for these two acids. Taken together, these data suggest that anhydrous proton transport in the phosphonic and phosphinic acid model compounds occurs primarily by a structure-diffusion, hopping-based mechanism rather than a vehicle mechanism. Further analysis of ionic conductivity and ion self-diffusion rates by using the Nernst-Einstein equation reveals that the phosphonic and phosphinic acid model compounds are relatively highly dissociated even under anhydrous conditions. In contrast, sulfonic and carboxylic acid-based systems exhibit relatively low degrees of dissociation under anhydrous conditions. These findings suggest that fluoroalkyl phosphonic and phosphinic acids are good candidates for further development as anhydrous, high-temperature proton conductors.

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Section: Nernst-einstein Relation and Haven Ratiosupporting

confidence: 85%

Perfluoroalkyl Phosphonic and Phosphinic Acids as Proton Conductors for Anhydrous Proton‐Exchange Membranes

et al. 2010

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“…This problem has been analyzed in refs. [34,35] and strategies to overcome this problem have been suggested.…”

Section: Discussionmentioning

confidence: 99%

“…The latter is frequently observed for proton conductors with a high concentration of mobile protons, which may be translocated on closed trajectories (e.g. in ring exchange processes) as observed for proton diffusion in the plastic phases of alkaline metal hydroxides [33,34], in phosphoric acid [32] and in phosphonic acid [35]. In all cases, regions containing excess protons must be charge compensated by proton deficient regions with electrostatic attraction between these regions (defects) that depends on their mutual separation distance and the dielectric constant of the medium.…”

Section: Self-diffusion Coefficients Of Cyclic Oligomersmentioning

confidence: 99%

Anhydrous Polymeric Proton Conductors Based on Imidazole Functionalized Polysiloxane

et al. 2006

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Intrinsically proton conducting polymers with imidazole as proton solvent tethered to a polysiloxane backbone via a flexible spacer have been synthesized. Apart from the standard characterization also their thermal properties and transport behavior have been investigated. The materials exhibit proton conductivity as a consequence of self‐dissociation of the imidazole moieties and “structure diffusion” of the resulting defects. In particular, no liquid phase such as water or monomeric imidazole is needed for the observed proton conductivities.To study the influence of the tether structure on the transport properties, cyclic oligomers and open chain polymers with different spacer lengths have been synthesized.The materials are thermally stable up to 200 °C and become soft around room temperature. The conductivity exhibits VTF and WLF behavior with maximum conductivities around σ = 1.5.10–3 S cm–1 at T = 160 °C. The activation volume of the conductivity as derived from pressure dependent measurements is found to be unusually high. The lowest activation volumes and the highest conductivities are observed for the materials with the highest segmental mobilities, i.e. the longest spacers.Proton self‐diffusion coefficients as obtained from PFG NMR diffusion measurements are significantly higher than expected from the proton conductivities obtained by dielectric spectroscopy. This corresponds to unusually high Haven ratios which have been interpreted by correlated proton transfers allowing for fast proton diffusion while minimizing the separation of ionic charge carriers.

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“…The Grotthuss mechanism can also be present in low-mid temperature PEMs at high levels of hydration since water molecules can act as proton accepting media. The Grotthuss mechanism also provides insight on proton transport through PEMs operating at high temperatures and under non-humidified conditions, because some liquids with hydrogen bonding sites (such as phosphoric acid, imidazole and triazole) can act as proton accepting media with high degree of self dissociation [9,[20][21][22][23]. PEMs for each operating condition have thus been developed by considering both transport mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Sulfonated hydrocarbon membranes for medium-temperature and low-humidity proton exchange membrane fuel cells (PEMFCs)

Park

Lee

Guiver

2011

Progress in Polymer Science

611

229

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Proton conductivity and diffusion study of molten phosphonic acid H3PO3

Cited by 64 publications

References 35 publications

Perfluoroalkyl Phosphonic and Phosphinic Acids as Proton Conductors for Anhydrous Proton‐Exchange Membranes

Perfluoroalkyl Phosphonic and Phosphinic Acids as Proton Conductors for Anhydrous Proton‐Exchange Membranes

Anhydrous Polymeric Proton Conductors Based on Imidazole Functionalized Polysiloxane

Sulfonated hydrocarbon membranes for medium-temperature and low-humidity proton exchange membrane fuel cells (PEMFCs)

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