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On the activity and stability of Sr3NiPtO6 and Sr3CuPtO6 as electrocatalysts for the oxygen reduction reaction in a polymer electrolyte fuel cell
Chalmers tekniska högskola, Göteborg.
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.ORCID iD: 0000-0001-9203-9313
Chalmers tekniska högskola, Göteborg.
2007 (English)In: Journal of Power Sources, ISSN 0378-7753, Vol. 168, no 2, 346-350 p.Article in journal (Refereed) Published
Abstract [en]

Sr3NiPtO6 and Sr3CUPtO6 were evaluated as low-platinum alternative oxygen reduction catalysts in a solid polymer electrolyte fuel cell at 80 degrees C. The oxides were synthesised using a new method based on an organometallic precursor route. The electrochemical evaluation showed similar oxygen reduction performance for Sr3NiPtO6 and Sr3CUPtO6, with a slightly higher activity for Sr3NiPtO6. In comparison with the oxides, the oxygen reduction activity for a commercial Pt/C catalyst was approximately 10 times higher. XRD analysis of the used electrodes revealed that the oxides were not stable in the PEMFC environment, and converted into platinum during operation. Elemental analysis of the used electrodes also showed a difference in platinum formation, where the platinum content on the surface of the electrode facing the gas diffusion layer was several times higher for Sr3NiPtO6 than Sr3CUPtO6. This indicates that the Sr3NiPtO6 electrode may be more susceptible to platinum migration.

Place, publisher, year, edition, pages
2007. Vol. 168, no 2, 346-350 p.
Keyword [en]
platinum oxide; Sr3NiPtO6; Sr3CuPtO6; fuel cell; PEMFC
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-7240DOI: 10.1016/j.jpowsour.2007.02.051ISI: 000247055200007Scopus ID: 2-s2.0-34247632579OAI: oai:DiVA.org:kth-7240DiVA: diva2:12193
Note
QC 20100706Available from: 2007-05-31 Created: 2007-05-31 Last updated: 2010-07-06Bibliographically approved
In thesis
1. Evaluating Cathode Catalysts in the Polymer Electrolyte Fuel Cell
Open this publication in new window or tab >>Evaluating Cathode Catalysts in the Polymer Electrolyte Fuel Cell
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The polymer electrolyte membrane fuel cell (PEMFC) converts the chemical energy of hydrogen and oxygen (air) into usable electrical energy. At the cathode (the positive electrode), a considerable amount of platinum is generally required to catalyse the sluggish oxygen reduction reaction (ORR). This has implications regarding the cost in high-power applications, and for making a broad commercialisation of the PEMFC technology possible, it would be desirable to lower the amount of Pt used to catalyse the ORR.

In this thesis a number of techniques are described that have been developed in order to investigate catalytic activity at the cathode of the PEMFC. These methodologies resemble traditional three-electrode research in liquid electrolytes, including cyclic voltammetry in inert gas, but with the advantage of performing the experiments in the true PEMFC environment.

From the porous electrode studies it was seen that it is possible to reach mass activities close to 0.2 gPt/kW at potentials above 0.65 V at 60 ◦C, but that the mass activities may become considerably lower when raising the temperature to 80 ◦C and changing the measurement methodology regarding potential cycling limits and electrode manufacturing.

The model electrode studies rendered some interesting results regarding the ORR at the Pt/Nafion interface. Using a novel measurement setup for measuring on catalysed planar glassy carbon disks, it was seen that humidity has a considerable effect on the ORR kinetics of Pt. The Tafel slopes become steeper and the activity decreases when the humidity level of the inlet gases decreases. Since no change in the the electrochemical area of the Pt/Nafion interface could be seen, these kinetic phenomena were ascribed to a lowered Pt oxide coverage at the lower humidity level, in combination with a lower proton activity.

Using bi-layered nm-thick model electrodes deposited directly on Nafion membranes, the behaviour of TiO2 and other metal oxides in combination with Pt in the PEMFC environment was investigated. Kinetically, no intrinsic effect could be seen for the model electrodes when adding a metal oxide, but compared to porous electrodes, the surface (specific) activity of a 3 nm film of Pt deposited on Nafion seems to be higher than for a porous electrode using ∼4 nm Pt grains deposited on a carbon support. Comparing the cyclic voltammograms in N2, this higher activity could be ascribed to less Pt oxide formation, possibly due to a particle size effect.

For these bi-layered films it was also seen that TiO2 may operate as a proton-conducting electrolyte in the PEMFC.

Abstract [sv]

I polymerelektrolytbränslecellen (PEMFC) omvandlas den kemiska energin hos vätgas och syrgas (luft) direkt till användbar elektrisk energi. På katoden (den positiva elektroden) krävs betydande mängder platina för att katalysera den tröga syrereduktionsreaktionen (ORR). Detta inverkar på kostnaden för högeffektsapplikationer, och för att göra en bred kommersialisering av PEMFC-teknologin möjlig skulle det vara önskvärt att minska den Pt-mängd som används för att katalysera ORR. I denna avhandling beskrivs ett antal tekniker som utvecklats för att undersöka katalytisk aktivitet på katoden i PEMFC. Metodiken liknar traditionella treelektrodexperiment i vätskeformig elektrolyt, med cyklisk voltammetri i inert gas, men med fördelen att försöken utförs i den riktiga PEMFC-miljön. I försök med porösa elektroder visades att det är möjligt att nå massaktiviteter nära 0.2 gPt/kW för potentialer över 0.65 V vid 60 ◦C, men massaktiviteterna kan bli betydligt lägre om temperaturen höjs till 80 ◦C, och om potentialsvepgränser och elektrodentillverkningsmetod ändras. Försök med modellelektroder resulterade i intressanta resultat rörande ORR i gränsskiktet Pt/Nafion. Genom att använda en ny metodik för att mäta på katalyserade plana elektroder av vitröst kol (glassy carbon), var det möjligt att se att gasernas fuktighet har en betydande inverkan på ORR-kinetiken hos Pt. Tafellutningarna blir brantare och aktiviteten minskar när inloppsgasernas fuktighetsgrad minskar. Eftersom den elektrokemiska arean hos Pt/Nafion-gränsskiktet inte ändrades, ansågs dessa kinetiska effekter bero på en lägre täckningsgrad av Ptoxider vid lägre fuktigheter, i kombination med lägre protonaktivitet. Genom att använda Nafionmembran belagda med nm-tjocka tvåskiktsmodellelektroder undersöktes hur Pt i kombination med TiO2 och andra metalloxider verkar i PEMFC-miljön. Kinetiskt sett hade tillsatsen av metalloxider ingen inre påverkan på aktiviteten, men vid jämförelse med porösa elektroder tycks den specifika ytaktiviteten vara högre hos en 3 nm film av Pt på Nafion än för en porös elektrod baserad på ∼4 nm Pt-korn belagda på ett kolbärarmaterial. Jämför man de cykliska voltammogrammen i N2, kan den högre aktiviteten tillskrivas en lägre grad av Pt-oxidbildning, vilket i sin tur kan bero på en storlekseffekt hos Pt-partiklarna. Försöken med dessa tvåskiktselektroder visade också att TiO2 kan verka som protonledande elektrolyt i PEMFC.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. xii, 50 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:39
Keyword
fuel cell, humidity, model electrodes, Nafion, oxygen reduction, PEMFC, platinum, polymer electrolyte, thin film evaporation, titanium oxide, bränslecell, fuktighet, modellelektroder, Nafion, PEMFC, platina, polymerelektrolyt, syrereduktion, tunnfilmsförångning, titanoxid
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-4413 (URN)978-91-7178-714-9 (ISBN)
Public defence
2007-06-11, D2, Lindstedsvägn 5, Stockholm, 13:00
Opponent
Supervisors
Note
QC 20100706Available from: 2007-05-31 Created: 2007-05-31 Last updated: 2010-07-06Bibliographically approved

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