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Synthesis of palladium nanoparticles decorated helical carbon nanofiber as highly active anodic catalyst for direct formic acid fuel cells
Umeå University, Faculty of Science and Technology, Department of Physics.
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2012 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 0019-4686, Vol. 63, 323-328 p.Article in journal (Refereed) Published
Abstract [en]

We present a single metal approach to produce highly active catalyst materials based on Pd-decorated helical carbon nanofibers. Helical carbon fibers are synthesized by a chemical vapor deposition process on a C-60 supported Pd catalyst and the obtained fibers are functionalized by H2O2 followed by a decoration with Pd nanoparticles. Although transmission electron microscopy images show that the decoration is relatively inhomogeneous the electrocatalytic activity for formic acid oxidation is very high. Cyclic voltammetry measurements (CV) show that the generated current peak value for Pd-decorated helical carbon nanofibers is 300 mA/mg(Pd) for a scan rate of 10 mV/s. This is significantly higher than the corresponding value of a reference sample of multiwalled carbon nanotubes decorated with Pd nanoparticles by the same process. Fuel cell tests for our Pd-decorated helical carbon nanofibers also displayed a high power density, although not as superior to Pd-decorated multiwalled nanotubes as measured by CV. Our results show that helical carbon nanofibers have several good properties, such as a rigid anchoring of catalyst nanoparticles and a suitable structure for creating functionalization defects which make them an interesting candidate for electrochemical applications. (C) 2012 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
Oxford: Pergamon Press, 2012. Vol. 63, 323-328 p.
Keyword [en]
Helical carbon fibers, Electrochemistry, Transmission electron microscopy, Catalyst, Palladium, Fuel cells, Formic acid
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Chemical Sciences
URN: urn:nbn:se:umu:diva-54138DOI: 10.1016/j.electacta.2011.12.104ISI: 000301468800046OAI: diva2:516928
Available from: 2012-04-20 Created: 2012-04-17 Last updated: 2013-04-29Bibliographically approved
In thesis
1. Synthesis and characterization of palladium based carbon nanostructure-composites and their clean-energy application
Open this publication in new window or tab >>Synthesis and characterization of palladium based carbon nanostructure-composites and their clean-energy application
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Carbon nanostructures are a wide field with many applications. The use of carbon nanostructures as support in heterogeneous catalysis is a key development that led together with the use of nanoparticles to a significant cost reduction of catalysts. Catalysts designed in this way are widely applied in fuel cell technologies. For portable devices especially low temperature fuel cells are desirable with low hazards for the user. One technology which fulfills these requirements is the direct formic acid fuel cell (DFAFC). DFAFC have many promising characteristics, such as high electromotive force and easy fuel handling. However, they still suffer from too low power output and lifetime for commercialization.

This thesis focusses on two main aspects: the synthesis of carbon nanostructures by chemical vapor deposition (CVD) and their application as catalyst support. The materials are investigated by many different techniques ranging from transmission electron microscopy (TEM) to fuel cell tests.

Different carbon nanostructures could be synthesized by catalytic CVD on palladium (Pd) nanoparticles. Multi-walled carbon nanotubes (MWCNTs), carbon nanofibers (CNFs) and helical carbon nanofibers (HCNFs) were grown, selectively, dependent on temperature, using acetylene as carbon precursor. Especially HCNF raised further interest due to their unique structure. A growth model for HCNFs was developed based on an anisotropic extrusion model. The synthesis conditions for HCNFs were optimized until an almost 100 % purity with very high efficiency was obtained.

The unique helical but fiber-like structure made the material very interesting as support for heterogeneous catalysis. Several catalysts based on Pd nanoparticle decorated HCNFs were developed. The synthesis methods ranged from standard methods like the polyol method to phase-transfer methods. The catalysts showed very promising results for the electro-oxidation of methanol, ethanol and formic acid. This makes them highly attractive for fuel cell applications. The catalysts were tested in DFAFC. The superiority of HCNF-based catalysts is attributed to the good attachment of nanoparticles to the defect-rich and easy to functionalize surface of HCNFs in combination with adequate film forming properties during electrode preparation.

Abstract [sv]

Nanostrukturerat kol är ett mycket brett fält med ett stort antal tillämpningar. Användning av kolnanostrukturer som support för heterogena katalysmaterial har tillsammans med utvecklingen av nanopartiklar lett till en avsevärd minskning av kostnaden för katalysatorer. Katalysatorer designade på detta sätt används frekvent i bränsleceller. För portabla tillämpningar är utvecklingen av säkra och miljövänliga lågtemperaturceller mycket viktig. En teknologi som uppfyller dessa kriterier är bränsleceller som drivs med myrsyra (DFAFC). Sådana bränsleceller har många önskvärda egenskaper, såsom en hög elektromotorisk kraft och en enkel hantering av bränslet. Trots dessa goda egenskaper har de också en del nackdelar som hindrar en full kommersialisering. De två mest problematiska är en för låg genererad effekt samt en för kort livslängd på katalysatorerna.

Denna avhandling fokuserar på två huvudpunkter som adresserar dessa problem; tillverkning och karaktärisering av kolnanostrukturer producerade med CVD, och deras tillämpningar som support för katalysatorer. Materialen karaktäriseras med en rad olika tekniker, allt från transmission-elektronmikroskopi till bränslecellstester.

Olika kolnanostrukturer har syntetiserats med katalytisk CVD på palladium (Pd) nanopartiklar. Produktionen av flerväggiga kolnanorör, kolfibrer och heliska kolnanofibrer har tillverkats med acetylen som kolkälla och genom att variera temperaturen kunde innehållet av olika typer av nanostrukturerat kol kontrolleras. Särskilt stort intresse har de heliska kolnanofibrerna rönt på grund av deras unika struktur. Vi beskriver en tillväxtmekanism baserad på en anisotrop diffusionsmodell. Genom att justera produktionsparametrarna visar vi att heliska kolnanofibrer kunde tillverkas med nära 100 %-ig renhet och hög effektivitet.

Den unika heliska och fiberlika strukturen är mycket intressant for tillämpningar som support för heterogena katalysatorer. Ett flertal kompositer för katalytiska tillämpningar har utvecklats baserade på heliska kolnanofibrer, dekorerade med heterogena katalysatorer genom en rad olika kemiska/fysikaliska tekniker. De syntetiserade materialen visar mycket goda katalytiska egenskaper för att oxidera metanol, etanol och myrsyra. Därigenom blir de mycket attraktiva för användning i bränsleceller. Vi korrelerar de goda katalytiska egenskaperna med en bra vidhäftning av nanopartiklarna på de heliska kolnanofibrerna defekter, deras goda ledningsförmåga, bra egenskaper för att förbereda elektroder, samt deras stora yta i förhållande till deras volym och vikt.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2013. 66 p.
Carbon nanostructures, chemical vapour deposition, electro catalysts, transmission electron microscopy, direct formic acid fuel cells
National Category
Condensed Matter Physics
Research subject
Solid State Physics
urn:nbn:se:umu:diva-68852 (URN)digital version: 978-91-7459-632-8 (ISBN)printed version:978-91-7459-631-1 (ISBN)
Public defence
2013-05-31, Naturvetarhuset, N450, Umeå Universitet, Umeå, 13:00 (English)
Knut and Alice Wallenberg FoundationSwedish Research Council
Available from: 2013-05-07 Created: 2013-04-26 Last updated: 2013-04-29Bibliographically approved

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