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Performance recovery after contamination with nitrogen dioxide in a PEM fuel cell
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.ORCID iD: 0000-0001-9653-6835
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

While the market of fuel cell vehicles is increasing, these vehicles will still coexist with combustion engine vehicles on the roads and will be exposed to an environment with significant amounts of contaminants that will decrease the durability of the fuel cell. In order to investigate different recovery methods, a PEM fuel cell is in this study contaminated with 100 ppm of NO2 at the cathode side. The possibility to recover the cell performance is studied by using different airflow rates, different current densities, and by subjecting the cell to successive polarization curves. The results show that the successive polarization curves are the best choice for recovery; it took 35 min to reach full recovery of cell performance, compared to 4.5 hours of recovery with pure air at 0.5 A cm-2 and 110 ml min-1. However, the performance recovery at a current density of 0.2 A cm-2 and air flow 275 ml min-1 was done in 66 min, which is also a possible alternative. Additionally, two operation techniques are suggested and compared during 7 h of operation; air recovery and air depletion. The air recovery technique shows to be a better choice than the air depletion technique.

National Category
Other Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-241907OAI: oai:DiVA.org:kth-241907DiVA, id: diva2:1282765
Note

QC 20190128

Available from: 2019-01-25 Created: 2019-01-25 Last updated: 2019-01-29Bibliographically approved
In thesis
1. On Gas Contaminants, and Bipolar Plates in Proton Exchange Membrane Fuel Cells
Open this publication in new window or tab >>On Gas Contaminants, and Bipolar Plates in Proton Exchange Membrane Fuel Cells
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The proton exchange membrane (PEM) fuel cell is an electrochemical device that converts chemical energy into electrical energy through two electrocatalytic reactions. The most common catalyst used is platinum on carbon (Pt/C), which has shown the best performance in the fuel cell until now. However, the drawback of this catalyst is that it does not tolerate impurities, and both hydrogen and oxygen may carry small amounts of impurities depending on the production sources. The purpose of this thesis is to understand the effect of two impurities that are less investigated, i.e., ammonia, which may accompany the hydrogen rich reformates from renewable sources, and nitrogen dioxide, which may come from air pollution. The mechanism of contamination and an adequate recovery method for the respective contaminant are studied. Additionally, electroplated bipolar plates with Ni-Mo and Ni-Mo-P coatings were tested as alternatives to stainless steel and carbon materials.

The results show that ammonia not only provokes changes in the polymer membrane but also in the oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR) and catalyst ionomer in both electrodes. The extent of performance recovery after the contamination depends on the concentration used and the exposure time. In contrast, nitrogen dioxide affects the catalyst in the electrode directly; the contamination is related to side reactions that are produced on the catalyst’s surface. However, NO2 is not attached strongly to the catalyst and it is possible to restore the performance by using clean air. The time the recovery process takes depends on the potential applied and the air flow.

Finally, the evaluation of electroplated Ni-Mo and Ni-Mo-P on stainless steel by ex situ and in situ studies shows that these coatings reduce the internal contact resistance (ICR) and the corrosion rate of the stainless steel considerably. However, the in situ experiments show that phosphorus addition to the coating does not improve the fuel cell performance; thus, the Ni-Mo alloy is found to be a promising choice for electroplating stainless steel bipolar plates.

Abstract [sv]

Polymerelektrolytbränslecellen är en elektrokemisk enhet som omvandlar den kemiskt bundna energin i ett bränsle till elektrisk energi genom två elektrokatalytiska reaktioner. Den vanligaste katalysatorn som används är Pt/C som hittills också har visat bäst prestanda i bränslecellen. Nackdelen med denna katalysator är dock att den inte tolererar föroreningar. Både vätgas och syrgas kan innehålla små mängder av föroreningar beroende på ursprung. Syftet med denna avhandling är att förstå effekten på cellens prestanda av två olika föroreningar som är mindre undersökta: Ammoniak som kan medfölja vid reformering av förnybara råvaror till vätgas, och kvävedioxid som kan komma från luftföroreningar. Mekanismer för förorening av cellen och en adekvat återhämtningsmetod för respektive förorening har studerats. Dessutom, bipolära plattor av rostfritt stål elektrokemiskt belagda med Ni-Mo eller Ni-Mo-P, undersökts som ett alternativ till rent rostfritt stål- och grafit.

Resultaten visar att ammoniak inte bara åstadkommer förändringar i polymermembranet utan också i syrereduktionsreaktionen (ORR), väteoxidationsreaktionen (HOR) och jonomeren i de båda elektroderna. Till vilken grad som försämrad prestanda efter förorening kan återhämtas, beror både på koncentrationen av ammoniak och exponeringstid. När det gäller kvävedioxid så påverkar en bara elektrodens katalysator där försämringen av elektroden är relaterad till sidoreaktioner som sker på katalysatorytan. NO2 är dock inte starkt bunden till katalysatorn och det är möjligt att återhämta prestandan med bara ren luft. Tiden som återhämtningsprocessen tar beror på cellpotentialen och luftflödet.

Utvärderingen av elektropläterade skikt av Ni-Mo och Ni-Mo-P på rostfritt stål, som gjorts genom mätningar ex-situ och in-situ, visar att dessa beläggningar avsevärt minskar det interna kontaktmotståndet (ICR) och korrosionen av rostfritt stål. In-situ-experimenten visar att tillsatsen av  fosfor i beläggningen inte förbättrar bränslecellens prestanda, men att legering av Ni-Mo är ett lovande material att använda vid elektroplätering av skyddande skikt på bipolära plattor av rostfritt stål.

Place, publisher, year, edition, pages
Stockholm: Kungliga Tekniska högskolan, 2019. p. 58
Series
TRITA-CBH-FOU ; 2019:6
Keywords
PEM fuel cell, contaminants, ammonia, nitrogen dioxide, degradation, recovery, bipolar plates, electroplating, Ni-Mo, Ni-Mo-P, internal contact resistance, PEM bränslecell, föroreningar, ammoniak, kvävedioxid, degradering, återhämtning, bipolära plattor, elektroplätering, Ni-Mo, Ni-Mo-P, interna kontaktmotståndet
National Category
Other Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-241911 (URN)978-91-7873-092-6 (ISBN)
Public defence
2019-02-28, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20190128

Available from: 2019-01-28 Created: 2019-01-25 Last updated: 2019-01-28Bibliographically approved

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