Why do proton conducting polybenzimidazole phosphoric acid membranes perform well in high-temperature PEM fuel cells?

Melchior, Jan-Patrick; Majer, G.; Kreuer, Klaus‐Dieter

doi:10.1039/c6cp05331a

Cited by 136 publications

(127 citation statements)

References 64 publications

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“…12,13 Thus, it is possible that migration transfer of electrolyte ions is promoted at high current densities owing to the consequential increase of humidity. Any phosphate anions that migrate to the anode will recombine with the protons that are continuously formed there, leading to accumulation of phosphoric acid in this region.…”

Section: Resultsmentioning

confidence: 99%

“…In a similar fashion, any hydronium cations that migrate to the cathode will be reduced upon reaching their destination, causing electroosmotic water drag and accumulation of water in that region. 12,13 Quite probably, this will promote acid loss via the same mechanisms, perhaps with additional influence from decreased viscosity and from the proposed steam distillation mechanism. 9 Obviously, migration transfer will become more prominent as the current density (rate of charge transport) increases because it is tantamount to transporting a larger amount of ions.…”

Section: Resultsmentioning

confidence: 99%

“…0.97). 5,7,[10][11][12][13] For phosphoric acid, such deviation becomes more pronounced the farther away the water content is deviating from the composition that corresponds to H 3 PO 4 .12 As such, migration of electrolyte ions may be encouraged both by condensation and by uptake of water, partly because of consequential formation of charged phosphates or hydronium ions. As a result, the ionic conductivity in phosphoric acid, which is usually ascribed to structural diffusion of protons via the Grotthuss mechanism, might in part be attributed to migration transfer of ions * Electrochemical Society Member.…”

mentioning

confidence: 99%

“…0.97). 5,7,[10][11][12][13] For phosphoric acid, such deviation becomes more pronounced the farther away the water content is deviating from the composition that corresponds to H 3 PO 4 .…”

mentioning

confidence: 99%

mentioning

confidence: 99%

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Long-Term Durability of PBI-Based HT-PEM Fuel Cells: Effect of Operating Parameters

Søndergaard

Cleemann

Becker

et al. 2018

J. Electrochem. Soc.

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This work studies the long-term durability of high-temperature polymer electrolyte membrane fuel cells based on acid-doped polybenzimidazole membranes. The primary focus is on acid loss via the evaporation mechanism, which is a major cause of degradation in applications that involve long-term operation. Durability is assessed for 16 identically fabricated membrane electrode assemblies (MEAs), and evaluations are carried out using operating parameters as stressors with gas stoichiometries ranging from 2 to 25, current densities from 200 to 800 mA cm −2 , and temperatures of 160 or 180 • C. Cell diagnostics are composed of time resolved polarization curves, post mortem analysis, and in situ temperature measurements. A major part of the cell degradation during these steady-state tests can be ascribed to increasing area-specific series resistance. By means of post mortem acid-loss measurements, the degradation is correlated to the temperature and to the accumulated gas-flow volume. Such relations are indicative of acid loss via evaporation. Current density also plays a critical role for the acid loss and, thus, for the overall cell degradation. The effect of current is likely tied to mechanisms that involve water generation, migration of electrolyte ions, and locally elevated temperature inside the Since the polybenzimidazole (PBI) polymer acts as a Brønsted base in relation to phosphoric acid, membranes of PBI can be doped with phosphoric acid through acid-base complexation. Some of the H 3 PO 4 molecules, 2 per polymer repeat unit, are then bound to the basic functional sites of the polymer. However, excess acid is essential in order to attain a conductivity that is high enough for use as electrolyte in a polymer electrolyte membrane fuel cell (PEMFC). Fuel cells based on this type of electrolyte are known as high-temperature (HT-)PEMFCs, typically operating at temperatures of 140-180• C. Phosphoric acid-doped PBI membranes can be prepared either by direct (or so-called sol-gel) casting from a solution of PBI dissolved in polyphosphoric acid (PPA) or by solution casting of a PBI film via solvent evaporation, for which acid-doping follows subsequently. 1 For HT-PEMFCs, the cell performance usually increases to a stable state within the first few hundred hours of operation. This activation of the cell might be a consequence of acid redistribution in the membrane electrode assembly (MEA).2-4 Such redistribution of acid also implies susceptibility to its loss, however, because it is a testament to the mobility of the doping-acid. [5][6][7] As reviewed by Jakobsen et al., a number of mechanisms have been proposed to explain the loss of doping-acid from PBI membranes, including evaporation into the gas phase and a so-called steam distillation mechanism, the latter of which has been proposed governed by temperature as well as humidity. 9 Migration of electrolyte ions might also be an issue with respect to acid loss, particularly if the proton transference number deviates significantly from the maximum value for phosphori...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

“…0.97). 5,7,[10][11][12][13] For phosphoric acid, such deviation becomes more pronounced the farther away the water content is deviating from the composition that corresponds to H 3 PO 4 .…”

mentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

Long-Term Durability of PBI-Based HT-PEM Fuel Cells: Effect of Operating Parameters

Søndergaard

Cleemann

Becker

et al. 2018

J. Electrochem. Soc.

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Porous Proton Exchange Membrane with High Stability and Low Hydrogen Permeability Realized by Dense Double Skin Layers Constructed with Amino tris (methylene phosphonic acid)

Zhang

Wang

et al. 2022

Adv Funct Materials

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Porous proton exchange membranes (PEMs) with abundant porous structures show enhanced phosphoric acid (PA) doping levels and proton transport capability. However, the high PA loss rate and serious hydrogen cross-over lead to poor membrane stability. Enhancing the stability of PA-doped porous PEMs is therefore crucial for obtaining high-performance proton exchange membrane fuel cells. Herein, a porous polybenzimidazole membrane with dense double skin layers is reported using amino tris (methylene phosphonic acid) (ATMP) constructed. This membrane effectively alleviates hydrogen permeation and PA loss in a water/anhydrous environment and exhibits enhanced stability. Surprisingly, as an organic proton conductor, ATMP has strong hydrogen bonding with PA, leading to the formation of more continuous proton transport channels. Due to the dense double skin layers protection and the synergistic mass transfer of ATMP and PA, the porous membrane shows excellent proton conductivity (0.112 S cm −1 ) and a H 2 -O 2 fuel cell peak power density of 0.98 W cm −2 at 160 °C. Moreover, it presents excellent fuel cell stability, with a voltage decay rate of only 5.46 µV h −1 . In addition, the porous membrane surpasses the traditional working temperature range, operating in the range of 80-220 °C. This study provides new insight into developing high-performance porous PEMs.

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Acid‐in‐Clay Electrolyte for Wide‐Temperature‐Range and Long‐Cycle Proton Batteries

et al. 2022

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Proton conduction underlies many important electrochemical technologies. A family of new proton electrolytes is reported: acid‐in‐clay electrolyte (AiCE) prepared by integrating fast proton carriers in a natural phyllosilicate clay network, which can be made into thin‐film (tens of micrometers) fluid‐impervious membranes. The chosen example systems (sepiolite–phosphoric acid) rank top among the solid proton conductors in terms of proton conductivities (15 mS cm−1 at 25 °C, 0.023 mS cm−1 at −82 °C), electrochemical stability window (3.35 V), and reduced chemical reactivity. A proton battery is assembled using AiCE as the solid electrolyte membrane. Benefitting from the wider electrochemical stability window, reduced corrosivity, and excellent ionic selectivity of AiCE, the two main problems (gassing and cyclability) of proton batteries are successfully solved. This work draws attention to the element cross‐over problem in proton batteries and the generic “acid‐in‐clay” solid electrolyte approach with superfast proton transport, outstanding selectivity, and improved stability for room‐ to cryogenic‐temperature protonic applications.

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Why do proton conducting polybenzimidazole phosphoric acid membranes perform well in high-temperature PEM fuel cells?

Cited by 136 publications

References 64 publications

Long-Term Durability of PBI-Based HT-PEM Fuel Cells: Effect of Operating Parameters

Long-Term Durability of PBI-Based HT-PEM Fuel Cells: Effect of Operating Parameters

Porous Proton Exchange Membrane with High Stability and Low Hydrogen Permeability Realized by Dense Double Skin Layers Constructed with Amino tris (methylene phosphonic acid)

Acid‐in‐Clay Electrolyte for Wide‐Temperature‐Range and Long‐Cycle Proton Batteries

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