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On Gas Contaminants, and Bipolar Plates in Proton Exchange Membrane Fuel Cells
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.ORCID iD: 0000-0001-9653-6835
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 [en]
PEM fuel cell, contaminants, ammonia, nitrogen dioxide, degradation, recovery, bipolar plates, electroplating, Ni-Mo, Ni-Mo-P, internal contact resistance
Keywords [sv]
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: urn:nbn:se:kth:diva-241911ISBN: 978-91-7873-092-6 (electronic)OAI: oai:DiVA.org:kth-241911DiVA, id: diva2:1282780
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
List of papers
1. Ammonia contamination of a proton exchange membrane fuel cell
Open this publication in new window or tab >>Ammonia contamination of a proton exchange membrane fuel cell
2018 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 165, no 3, p. F189-F197Article in journal (Refereed) Published
Abstract [en]

Reformate hydrogen from biogas is an attractive fuel alternative for energy conversion in PEM fuel cells. However, in the reformate traces of ammonia may be found, e.g. if the biogas is produced from agricultural resources. In this investigation the effect of ammonia in the fuel gas, on each part of the fuel cell, is studied by cyclic voltammetry, electrochemical impedance spectroscopy (EIS), symmetrical hydrogen cell (H2|H2)- and real fuel cell operation. A considerable degradation in performance is observed by introducing 200 ppm ammonia. The results show that ammonia not only affects the polymer electrolyte membrane but also the oxygen reduction reaction (ORR) and catalyst ionomer in both electrodes, whereas the hydrogen oxidation reaction (HOR) is the worst affected. In the short-term, the performance is reversible if running the cell on neat hydrogen after ammonia exposure, but this does not apply for long-term exposure. A mitigation method with air bleed is tested but gives no improvement of the performance.

Place, publisher, year, edition, pages
Electrochemical Society, 2018
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-225020 (URN)10.1149/2.0761803jes (DOI)000431790700083 ()2-s2.0-85043771326 (Scopus ID)
Funder
StandUp
Note

QC 20180328

Available from: 2018-03-28 Created: 2018-03-28 Last updated: 2019-05-20Bibliographically approved
2. Effect of nitrogen dioxide impurities on PEM fuel cell performance
Open this publication in new window or tab >>Effect of nitrogen dioxide impurities on PEM fuel cell performance
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Air is the most practical and economical oxidant to feed to the cathode in a proton exchange membrane fuel cell (PEMFC). However, the air is accompanied by small amounts of impurities that affect the performance of the fuel cell. Among these, nitrogen dioxide is the impurity that has been least investigated, and its effect is not fully understood. In this study, a possible mechanism is proposed based on the contamination of the fuel cell at different concentrations and adsorption potentials, and by employing stripping cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The results at different concentrations showed that the catalyst sites are blocked by the adsorption of NO2, and that there is a non-linear relationship between the concentration and degradation. The degradation is suggested to be related to the formation of intermediate species, as also shown by the pseudo-inductive impedance at the concentration of 100 and 200 ppm. Furthermore, the cyclic voltammetry showed that there is an oxidation to NO3- at 1.05 V, followed by the reduction of this specie to NO2- at 0.68 V, and a subsequent reduction of NO2- to N2O and/or NH2OH.

National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-241905 (URN)
Note

QC 20190128

Available from: 2019-01-25 Created: 2019-01-25 Last updated: 2019-01-29Bibliographically approved
3. Performance recovery after contamination with nitrogen dioxide in a PEM fuel cell
Open this publication in new window or tab >>Performance recovery after contamination with nitrogen dioxide in a PEM fuel cell
(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:nbn:se:kth:diva-241907 (URN)
Note

QC 20190128

Available from: 2019-01-25 Created: 2019-01-25 Last updated: 2019-01-29Bibliographically approved
4. Evaluation of Ni-Mo and Ni-Mo-P Electroplated Coatings on Stainless Steel for PEM Fuel Cells Bipolar Plates
Open this publication in new window or tab >>Evaluation of Ni-Mo and Ni-Mo-P Electroplated Coatings on Stainless Steel for PEM Fuel Cells Bipolar Plates
Show others...
2016 (English)In: Fuel Cells, ISSN 1615-6846, E-ISSN 1615-6854, Vol. 16, no 6, p. 784-800Article in journal (Refereed) Published
Abstract [en]

Stainless steel bipolar plates (BPPs) are the preferred choice for proton exchange membrane fuel cells (PEMFCs); however, a surface coating is needed to minimize contact resistance and corrosion. In this paper, Ni–Mo and Ni–Mo–P coatings were electroplated on stainless steel BPPs and investigated by XRD, SEM/EDX, AFM and contact angle measurements. The performance of the BPPs was studied by corrosion and conduction tests and by measuring their interfacial contact resistances (ICRs) ex situ in a PEMFC set-up at varying clamping pressure, applied current and temperature. The results revealed that the applied coatings significantly reduce the ICR and corrosion rate of stainless steel BPP. All the coatings presented stable performance and the coatings electroplated at 100 mA cm−2showed even lower ICR than graphite. The excellent properties of the coatings compared to native oxide film of the bare stainless steel are due to their higher contact angle, crystallinity and roughness, improving hydrophobicity and electrical conductivity. Hence, the electroplated coatings investigated in this study have promising properties for stainless steel BPPs and are potentially good alternatives for the graphite BPP in PEMFC.

Place, publisher, year, edition, pages
John Wiley & Sons, 2016
Keywords
Alloys, Bipolar Plate, Electroplated Coatings, Fuel Cells, Interfacial Contact Resistance, Molybdenum, PEM Fuel Cell, Wettability, Alloying, Coatings, Contact angle, Contact resistance, Corrosion, Corrosion rate, Gas fuel purification, Graphite, Nickel, Oxide films, Proton exchange membrane fuel cells (PEMFC), Wetting, Bipolar plates, Electrical conductivity, Electroplated coating, Proton exchange membrane fuel cell (PEMFCs), Stable performance, Stainless steel bipolar plates, Stainless steel
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-201882 (URN)10.1002/fuce.201600062 (DOI)000392531900014 ()2-s2.0-84992349867 (Scopus ID)
Funder
StandUp
Note

QC 20170308

Available from: 2017-03-08 Created: 2017-03-08 Last updated: 2019-01-29Bibliographically approved
5. 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
Show others...
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: 2019-01-29Bibliographically approved

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