Evaluation of temperature and electrolyte concentration dependent Oxygen solubility and diffusivity in phosphoric acid

Fleige, M.; Holst-Olesen, K.; Wiberg, G. K. H.; Arenz, Matthias (2016). Evaluation of temperature and electrolyte concentration dependent Oxygen solubility and diffusivity in phosphoric acid. Electrochimica acta, 209, pp. 399-406. Elsevier Science 10.1016/j.electacta.2016.05.048

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Reactant diffusion and solubility is of utmost important for providing sufficient reactant concentrations at a catalytic active surface. In high temperature proton exchange membrane fuel cells (HT-PEMFCs) the electrolyte consists of concentrated phosphoric acid embedded into a polybenzimidazole (PBI) membrane. Despite the elevated operation temperature of 150 degrees C, the observed oxygen reduction reaction (ORR) rates in HT-PEMFCs are significantly lower than in low temperature PEMFCs. Reduced reactant transport in combination with site blocking is often mentioned as possible inhibition factors. As a step towards studying the ORR under realistic conditions in half-cell setups, in the present study we investigate the oxygen solubility and diffusivity in diluted phosphoric acid electrolyte in a temperature range of 5 to 80 degrees C. The presented work demonstrates and discusses under which conditions reliable data for these constants can be obtained. In particular it is shown that the product of oxygen solubility and diffusivity, which determines the oxygen mass transport, first increases as function of temperature, but then decreases again above 60 degrees C. It seems that the decrease in oxygen solubility at higher temperatures is correlated to an increase in the apparent ORR activation energy. (C) 2016 Elsevier Ltd. All rights reserved.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Departement of Chemistry and Biochemistry

UniBE Contributor:

Arenz, Matthias

Subjects:

500 Science > 570 Life sciences; biology
500 Science > 540 Chemistry

ISSN:

0013-4686

Publisher:

Elsevier Science

Language:

English

Submitter:

Matthias Arenz

Date Deposited:

21 Nov 2016 09:38

Last Modified:

10 May 2018 02:30

Publisher DOI:

10.1016/j.electacta.2016.05.048

Web of Science ID:

000379504600045

Uncontrolled Keywords:

phosphoric acid oxygen solubility oxygen diffusion coefficient ht-pemfc hydrodynamic chronocoulometry reduction reaction fuel-cells hydrodynamic chronocoulometry enhanced electrocatalysis polymer electrolyte vapor-pressure disc electrode platinum model coefficients

BORIS DOI:

10.7892/boris.89897

URI:

https://boris.unibe.ch/id/eprint/89897

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