The genuine ac-to-dc proton conductivity crossover of nafion and polymer dielectric relaxations as a fuel cell polarization loss
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2020
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Journal of Electroanalytical Chemistry
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The non-ohmic behavior of Nafion electrical properties, i. e., the thickness and potential dependent conductivity, was
studied in the impedance, dielectric and conductivity representations with the use of a special through-plane sampleholder
in a 4-probe array. Such measurements allowed identifying the genuine ac-to-dc conductivity crossover
frequency in Nafion, which occurs for f<10-1 Hz. In addition, the minimization of the interfacial electrode/ionomer
polarizations with the 4-probe setup permitted the determination of the bulk dc conductivity and dielectric constant of
Nafion, which are σ~0.03 Scm-1 and ε′~106 (T=40 °Cand RH=100%), respectively. The colossal dielectric constant
is shown to increase the Debye length of the electric double layer to values comparable to the membrane thickness.
Therefore, the exponential increase of the proton conductivity with increasing both membrane thickness and
electric potential are a result of canceling out the non-linear effects of electric double layer caused by the high dielectric
permittivity of Nafion. The ac-to-dc conductivity crossover in H2/O2 fuel cell impedance curves takes place for f<100
Hz and matches with the ex situ impedance spectroscopy study in excellent agreement, revealing a striking result: the
potential dependent conductivity of Nafion requires extra fuel cell overpotential to overcome the electrode/ionomer
interfacial polarization representing an additional polarization loss to polymer electrolyte fuel cells.
Como referenciar
MATOS, B.R. The genuine ac-to-dc proton conductivity crossover of nafion and polymer dielectric relaxations as a fuel cell polarization loss. Journal of Electroanalytical Chemistry, v. 871, p. 1-13, 2020. DOI: 10.1016/j.jelechem.2020.114357. Disponível em: http://repositorio.ipen.br/handle/123456789/31366. Acesso em: 19 Apr 2024.
Esta referência é gerada automaticamente de acordo com as normas do estilo IPEN/SP (ABNT NBR 6023) e recomenda-se uma verificação final e ajustes caso necessário.