New catalysts for miniaturized methanol fuel cells

Christoffer Mølleskov Pedersen

Research output: Book/ReportPh.D. thesis

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The methanol fuel cell is an interesting energy technology, capable of converting the chemical energy of methanol directly into electricity. The technology is specifically attractive for small mobile applications such as laptops, smartphones, tablets etc. since it offers almost instantaneously recharging by simply replacing the methanol liquid. The technology is currently being developed for hearing instruments in order to ease the handling of the device for users complaining about difficulties replacing the very small batteries in the hearing instrument. The technology has already been demonstrated by the Danish Technological Institute; however, for the technology to become more widely adapted, the power density of the fuel cell must be increased.
It is well known that a considerable part of the energy from the methanol is lost in the fuel cell during the conversion due to poor kinetics. The kinetics can however be improved by using a superior catalyst. Therefore, the aim of this thesis is to identify new catalyst material for methanol fuel cells. By analysing the performance of the standard catalysts (PtRu and Pt) currently being applied in methanol fuel cells as anode and cathode respectively, a benchmark is defined. This benchmark is used to compare catalysts for the different reactions taking place in a fuel cell such as hydrogen oxidation, methanol oxidation and oxygen reduction. In addition, different phenomena in the fuel cell such as CO poisoning of the hydrogen oxidation and methanol poisoning of the oxygen reduction are studied. Consequently, promising new candidates for replacing the standard catalyst are identified. One of these, Pt5Gd, exhibits improved oxygen reduction reaction activity even in the presence of methanol, thus making Pt5Gd an interesting candidate to replace the Pt catalyst in the methanol fuel cell cathode.
Having identified a potential new catalyst material, a fabrication method is needed. Because the catalytic properties of the catalyst material is inherent in the surface of the catalyst, the surface to volume ratio for the material must be as high as possible, which usually can only be achieved by making the material as nanoparticles. However, the problem of Pt5Gd and other Pt alloys with lanthanides or early transition metals is that these materials are very difficult to
synthesise chemically, especially in the more technological relevant nanoparticulate form. Therefore, a second objective of this thesis has been to investigate different synthesis routes. The thesis is able to demonstrate for the first time, chemical synthesised carbon supported metallic PtxGd, PtxY and PtxTb alloy nanoparticles. The synthesised nanoparticles are more active than Pt nanoparticles, but not as active as expected for these materials. Thus, the synthesis route is promising but needs further optimisation.
Original languageEnglish
PublisherDepartment of Physics, Technical University of Denmark
Number of pages188
Publication statusPublished - 2016


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