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Electrochemical evaluation of new materials in polymer electrolyte fuel cells
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.ORCID iD: 0000-0003-4770-9554
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Polymer electrolyte fuel cells (PEFC) convert the chemical energy in hydrogen to electrical energy and heat, with the only exhaust being water. Fuel cells are considered key in achieving a sustainable energy sector. The main obstacles to wide scale commercialization are cost and durability. The aim of this thesis is to evaluate new materials for PEFC to potentially lower cost and increase durability. To lower the amount of expensive platinum catalyst in the fuel cell, the activities of Pt-rare earth metal (REM) alloy catalysts have been tested. To improve the lifetime of the carbon support, the carbon corrosion properties of multi walled carbon nanotubes have been evaluated. To reduce the overall cost of fuel cell stacks, carbon coated and metal coated bipolar plates have been tested. To increase the performance and lifetime of anion exchange membranes, the water transport has been studied.

The results show that the Pt-REM catalysts had at least two times higher specific activity than pure platinum, and even higher activities should be obtainable if the surface structures are further refined.

Multi-walled carbon nanotubes had lower carbon corrosion than conventional carbon Vulcan XC-72. However, once severely corroded their porous structure collapsed, causing major performance losses.

The carbon coated metallic bipolar plates showed no significant increase of internal contact resistance (ICR) by cycling, suggesting that these coatings are stable in fuel cells. The NiMo- and NiMoP coated bipolar plates showed low ICR, however, presence of the coated bipolar plates caused secondary harmful effects on the polymer membrane and ionomer.

Considering the water transport through anion exchange membranes it was found that most membranes showed very similar water transport properties, with more water detected at both the anode and cathode when a current was applied. The most significant factor governing the water transport properties was the membrane thickness, with thicker membranes reducing the backflow of water from anode to cathode.

The results indicate that all of the new tested materials have the capability to improve the lifetime and reduce cost and thereby improve the overall performance of PEFC.

Abstract [sv]

Polymerelektrolytbränsleceller (PEFC) omvandlar den kemiskt bundna energin i vätgas till elektrisk energi och värme, med endast vatten som utsläpp. Bränsleceller ses som en viktig del i att skapa en hållbar energisektor. Det största hindret för kommersialisering är kostnaden och den begränsande livslängden. Syftet med denna avhandling är att utvärdera nya material som skulle kunna sänka kostnaden och öka hållbarheten av PEFC. För att minska mängden dyr platinakatalysator i bränslecellen har aktiviteten av legerade katalysatorer av platina och sällsynta jordartsmetaller testats. För att öka livslängden av bränslecellen har kolkorrosionsegenskaperna av flerväggade kolnanorör (MWCNT) utvärderats. För att kunna minska den totala kostnaden på bränslecellsstacken har kol- och metallbelagda bipolära plattor undersökts. För att öka livslängden och öka prestandan av anjonledande membran har vattentransportegenskaperna av dessa membran studerats.

Resultaten visar att de legerade katalysatorerna hade mer än två gånger högre elektrokemisk aktivitet än ren platina. Ännu högre elektrokemiska aktiviteter bör kunna erhållas om ytstrukturen kan förbättra ytterligare.

För MWCNT var kolkorrosionen lägre än för de konventionella kolpartiklarna av Vulcan XC-72. Efter mycket korrosion, kollapsade dock den porösa strukturen, vilket ledde till stora förluster i prestanda.

De kolbelagda bipolära plattorna uppvisade inga signifikanta ändringar i kontaktmotstånd (ICR) efter de elektrokemiska testerna. Detta betyder att de är stabila i bränsleceller. De NiMo- och NiMoP-belagda bipolära plattorna hade låga ICR-värden, dock ledde beläggningens närvaro till försämringar av membran- och elektrodegenskaper.

Alla testade anjonledande membran uppvisade liknande vattentransportegenskaper, med ökning av vatten på både anoden och katoden under drift. Membranens tjocklek visade sig ha störst påverkan på vattentransporten. Med tjockare membran detekterades mindre vatten på katoden, vilket betyder att tillbakaflödet av vatten hämmas av membranets tjocklek.

Sammanfattningsvis visar resultaten att alla nya testade material i alla fall till viss del kan lösa problemen med den höga kostnaden och korta livslängden och därmed öka den totala prestandan av PEFC.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. , p. 66
Series
TRITA-CBH-FOU ; 2019:50
Keywords [en]
Fuel cell, Pt-REM, Alloy catalyst, Multi walled carbon nanotubes, Bipolar plates, Water transport
Keywords [sv]
Bränslecell, Pt-REM, Legerad katalysator, Flerväggade kolnanorör, Bipolära plattor, Vattentransport
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-261102ISBN: 978-91-7873-326-2 (print)OAI: oai:DiVA.org:kth-261102DiVA, id: diva2:1357397
Public defence
2019-11-05, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 2019-10-04

Available from: 2019-10-04 Created: 2019-10-03 Last updated: 2019-10-04Bibliographically approved
List of papers
1. Fuel Cell Measurements with Cathode Catalysts of Sputtered Pt3Y Thin Films
Open this publication in new window or tab >>Fuel Cell Measurements with Cathode Catalysts of Sputtered Pt3Y Thin Films
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2018 (English)In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 11, no 9, p. 1438-1445Article in journal (Refereed) Published
Abstract [en]

Fuel cells are foreseen to have an important role in sustainable energy systems, provided that catalysts with higher activity and stability are developed. In this study, highly active sputtered thin films of platinum alloyed with yttrium (Pt3Y) are deposited on commercial gas diffusion layers and their performance in a proton exchange membrane fuel cell is measured. After acid pretreatment, the alloy is found to have up to 2.5 times higher specific activity than pure platinum. The performance of Pt3Y is much higher than that of pure Pt, even if all of the alloying element was leached out from parts of the thin metal film on the porous support. This indicates that an even higher performance is expected if the structure of the Pt3Y catalyst or the support could be further improved. The results show that platinum alloyed with rare earth metals can be used as highly active cathode catalyst materials, and significantly reduce the amount of platinum needed, in real fuel cells.

Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH, 2018
Keywords
electrocatalysis, fuel cells, platinum, rare earths, thin films
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-228426 (URN)10.1002/cssc.201800023 (DOI)000431975700006 ()29513396 (PubMedID)2-s2.0-85044870915 (Scopus ID)
Note

QC 20180529

Available from: 2018-05-29 Created: 2018-05-29 Last updated: 2019-10-03Bibliographically approved
2. Evaluation of rare earth metal alloy catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells
Open this publication in new window or tab >>Evaluation of rare earth metal alloy catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells
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(English)Manuscript (preprint) (Other academic)
Keywords
Proton exchange membrane fuel cell, Platinum rare earth metal alloy, Catalyst, Oxygen reduction reaction, Fuel cells
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-261208 (URN)
Note

QC 20191004

Available from: 2019-10-03 Created: 2019-10-03 Last updated: 2019-11-15Bibliographically approved
3. 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
4. Carbon corrosion properties and performance of multi-walled carbon nanotube support with and without nitrogen-functionalization in fuel cell electrodes
Open this publication in new window or tab >>Carbon corrosion properties and performance of multi-walled carbon nanotube support with and without nitrogen-functionalization in fuel cell electrodes
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(English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859Article in journal (Other academic) Submitted
Abstract [en]

Keywords
Carbon nanotubes, oxygen reduction, PEMFC, carbon corrosion, mass spectrometry
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-261219 (URN)
Note

QC 20191004

Available from: 2019-10-03 Created: 2019-10-03 Last updated: 2019-11-15Bibliographically approved
5. 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
6. 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
7. Performance of a PEM fuel cell using electroplated Ni–Mo and Ni–Mo–P stainless steel bipolar plates
Open this publication in new window or tab >>Performance of a PEM fuel cell using electroplated Ni–Mo and Ni–Mo–P stainless steel bipolar plates
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2017 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 164, no 13, p. F1427-F1436Article in journal (Refereed) Published
Abstract [en]

The performance and durability of 316L stainless steel bipolar plates (BPP) electroplated with Ni–Mo and Ni–Mo–P coatings are investigated in a proton exchange membrane fuel cell (PEMFC), using a commercial Pt/C Nafion membrane electrode assembly (MEA). The effect of the BPP coatings on the electrochemical performance up to 115 h is evaluated from polarization curves, cyclic voltammetry and electrochemical impedance spectroscopy together with interfacial contact resistance (ICR) measurements between the coatings and the gas diffusion layer. The results show that all the coatings decrease the ICR in comparison to that of uncoated 316L BPP. The Ni-Mo coated BPP shows a low and stable ICR and the smallest effects on MEA performance, including catalyst activity/usability, cathode double layer capacitance, and membrane and ionomer resistance build up with time. After electrochemical evaluation, the BPPs as well as the water effluents from the cell are examined by Scanning Electron Microscopy, Energy Dispersive and Inductively Coupled Plasma spectroscopies. No significant degradation of the coated surface or enhancement in metal release is observed. However, phosphorus addition to the coating does not show to improve its properties, as deterioration of the MEA and consequently fuel cell performance losses is observed.

Place, publisher, year, edition, pages
Electrochemical Society, 2017
National Category
Other Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-215731 (URN)10.1149/2.0771713jes (DOI)000418409800166 ()2-s2.0-85033682707 (Scopus ID)
Funder
StandUp
Note

QC 20171023

Available from: 2017-10-13 Created: 2017-10-13 Last updated: 2019-10-03Bibliographically approved

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