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Electrochemical properties of alternative polymer electrolytes in fuel cells
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fuel cells, using hydrogen as energy carrier, allow chemically‑stored energy to be utilized for many applications, including balancing the electrical grid and the propulsion of vehicles. To make the fuel cell technology more accessible and promote a sustainable energy society, this thesis focuses on alternative polymer electrolytes, as they can potentially lead to a lower cost and a more environmentally‑friendly fuel cell. The main subject is anion exchange membrane fuel cells (AEMFCs), for which the importance of gas diffusion electrode morphology and platinum electrode reactions are investigated. Properties of the membrane such as water flux during operation are evaluated. Furthermore, novel polymer electrolytes are studied: variations of poly(phenylene oxide)‑based membranes in AEMFCs; and cellulose‑based membranes in a proton exchange membrane fuel cell (PEMFC).

 

The AEMFC results show that the performance is dependent on the electrode morphology. Electrochemical experiments in a hydrogen/hydrogen cell combined with modelling show that the hydrogen oxidation reaction proceeds through the Tafel‑Volmer reaction pathway on platinum. Application of the model in a hydrogen/oxygen cell shows that the cathode has the slowest reaction rate. During operation, the water flux through the membrane is directed from the anode where water is produced to the cathode where it is consumed. This leads to an increase in water content at both electrodes, which implies that electrode flooding is more likely than dry‑out during operation. The effect of membrane thickness on water flux is shown to be larger than the effect of polymer structure for several different types of poly(phenylene oxide)‑based membranes. The comparison of these polymers also indicates that a high conductivity, for the relative humidity achieved in a fuel cell, promotes increased performance. Finally, the study of cellulose-based membranes in a PEMFC shows that cellulose as a renewable, natural polymer has promising properties, such as stable conductivity for relative humidities above 65 % and a low gas permeability.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. , p. 59
Series
TRITA-CBH-FOU ; 2019:64
Keywords [en]
fuel cell, anion exchange membrane, proton exchange membrane, electrode morphology, hydrogen oxidation reaction, water transport, poly(phenylene oxide), cellulose
Keywords [sv]
bränslecell, anjonledande membran, protonledande membran, elektrodstruktur, vätgasoxidation, vattentransport, poly(fenylenoxid), cellulosa
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-263095ISBN: 978-91-7873-365-1 (print)OAI: oai:DiVA.org:kth-263095DiVA, id: diva2:1366451
Public defence
2019-11-29, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2019-10-29 Created: 2019-10-29 Last updated: 2019-10-29Bibliographically approved
List of papers
1. Electrode parameters and operating conditions influencing the performance of anion exchange membrane fuel cells
Open this publication in new window or tab >>Electrode parameters and operating conditions influencing the performance of anion exchange membrane fuel cells
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2018 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 277, p. 151-160Article in journal (Refereed) Published
Abstract [en]

A deeper understanding of porous electrode preparation and performance losses is necessary to advance the anion exchange membrane fuel cell (AEMFC) technology. This study has investigated the performance losses at 50 °C for varied: Tokuyama AS-4 ionomer content in the catalyst layer, Pt/C loading and catalyst layer thickness at the anode and cathode, relative humidity, and anode catalyst. The prepared gas diffusion electrodes in the interval of ionomer-to-Pt/C weight ratio of 0.4–0.8 or 29–44 wt% ionomer content show the highest performance. Varying the loading and catalyst layer thickness simultaneously shows that both the cathode and the anode influence the cell performance. The effects of the two electrodes are shown to vary with current density and this is assumed to be due to non-uniform current distribution throughout the electrodes. Further, lowering the relative humidity at the anode and cathode separately shows small performance losses for both electrodes that could be related to lowered ionomer conductivity. Continued studies are needed to optimize, and understand limitations of, each of the two electrodes to obtain improved cell performance.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
AEMFC, Electrode morphology, Electrode performance, Ionomer content, Pt/C catalyst
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-228724 (URN)10.1016/j.electacta.2018.04.137 (DOI)000433044200017 ()2-s2.0-85046745654 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20180529

Available from: 2018-05-29 Created: 2018-05-29 Last updated: 2019-10-29Bibliographically approved
2. An Electrochemical Impedance Study of the Hydrogen Electrode Reaction in the Anion Exchange Membrane Fuel Cell
Open this publication in new window or tab >>An Electrochemical Impedance Study of the Hydrogen Electrode Reaction in the Anion Exchange Membrane Fuel Cell
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(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-263077 (URN)
Note

QC 20191030

Available from: 2019-10-29 Created: 2019-10-29 Last updated: 2019-10-30Bibliographically approved
3. Determination of kinetic parameters for the oxygen reduction reaction on platinum in an AEMFC
Open this publication in new window or tab >>Determination of kinetic parameters for the oxygen reduction reaction on platinum in an AEMFC
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(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-263091 (URN)
Note

QC 20191030

Available from: 2019-10-29 Created: 2019-10-29 Last updated: 2019-10-30Bibliographically approved
4. Quantifying water transport in anion exchange membrane fuel cells
Open this publication in new window or tab >>Quantifying water transport in anion exchange membrane fuel cells
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2019 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 44, no 10, p. 4930-4939Article in journal (Refereed) Published
Abstract [en]

Sufficient water transport through the membrane is necessary for a well-performing anion exchange membrane fuel cell (AEMFC). In this study, the water flux through a membrane electrode assembly (MEA), using a Tokuyama A201 membrane, is quantified using humidity sensors at the in- and outlet on both sides of the MEA. Experiments performed in humidified inert gas at both sides of the MEA or with liquid water at one side shows that the aggregation state of water has a large impact on the transport properties. The water fluxes are shown to be approximately three times larger for a membrane in contact with liquid water compared to vaporous. Further, the flux during fuel cell operation is investigated and shows that the transport rate of water in the membrane is affected by an applied current. The water vapor content increases on both the anode and cathode side of the AEMFC for all investigated current densities. Through modeling, an apparent water drag coefficient is determined to −0.64, indicating that the current-induced transport of water occurs in the opposite direction to the transport of hydroxide ions. These results implicate that flooding, on one or both electrodes, is a larger concern than dry-out in an AEMFC.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Anion exchange membrane fuel cell, Fuel cells, Relative humidity sensor, Water transport model
National Category
Energy Systems
Identifiers
urn:nbn:se:kth:diva-244325 (URN)10.1016/j.ijhydene.2018.12.185 (DOI)000459837700036 ()2-s2.0-85060083256 (Scopus ID)
Note

QC 20190306

Available from: 2019-03-06 Created: 2019-03-06 Last updated: 2019-10-29Bibliographically approved
5. Fuel cell evaluation of anion exchange membranes based on PPO with different cation placement
Open this publication in new window or tab >>Fuel cell evaluation of anion exchange membranes based on PPO with different cation placement
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(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-261220 (URN)
Note

QC 20191004

Available from: 2019-10-03 Created: 2019-10-03 Last updated: 2019-10-30Bibliographically approved
6. Highly proton conductive membranes based on carboxylated cellulose nanofibres and their performance in proton exchange membrane fuel cells
Open this publication in new window or tab >>Highly proton conductive membranes based on carboxylated cellulose nanofibres and their performance in proton exchange membrane fuel cells
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2019 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488Article in journal (Refereed) Epub ahead of print
Abstract [en]

The performance of thin carboxylated cellulose nanofiber-based (CNF) membranes as proton exchange membranes in fuel cells has been measured in situ as a function of CNF surface charge density (600 and 1550 μmol g−1), counterion (H+ or Na+), membrane thickness and fuel cell relative humidity (RH 55 to 95%). The structural evolution of the membranes as a function of RH, as measured by Small Angle X-ray Scattering, shows that water channels are formed only above 75% RH. The amount of absorbed water was shown to depend on the membrane surface charge and counter ions (H+ or Na+). The high affinity of CNF for water and the high aspect ratio of the nanofibers, together with a well-defined and homogenous membrane structure, ensures a proton conductivity exceeding 1 mS cm−1 at 30 °C between 65 and 95% RH. This is two orders of magnitude larger than previously reported values for cellulose materials and only one order of magnitude lower than Nafion 212. Moreover, the CNF membranes are characterized by a lower hydrogen crossover than Nafion, despite being ≈30% thinner. Thanks to their environmental compatibility and promising fuel cell performance the CNF membranes should be considered for new generation proton exchange membrane fuel cells.

National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-263094 (URN)10.1039/C9TA04898G (DOI)
Note

QC 20191030

Available from: 2019-10-29 Created: 2019-10-29 Last updated: 2019-10-30Bibliographically approved

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