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Evaluation of Ni-Mo and Ni-Mo-P Electroplated Coatings on Stainless Steel for PEM Fuel Cells Bipolar Plates
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
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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. Vol. 16, no 6, p. 784-800
Keywords [en]
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: urn:nbn:se:kth:diva-201882DOI: 10.1002/fuce.201600062ISI: 000392531900014Scopus ID: 2-s2.0-84992349867OAI: oai:DiVA.org:kth-201882DiVA, id: diva2:1079319
Funder
StandUp
Note

QC 20170308

Available from: 2017-03-08 Created: 2017-03-08 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)
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QC 20190128

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

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