| 1. |
- Fretz, Samuel Joseph, 1987, et al.
(författare)
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Influence of Iron Salt Anions on Formation and Oxygen Reduction Activity of Fe/N-Doped Mesoporous Carbon Fuel Cell Catalysts
- 2019
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 4:18, s. 17662-17671
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Tidskriftsartikel (refereegranskat)abstract
- Doping carbon materials with transition metal ions can greatly expand their utility, given these metal ions' unique catalytic activity, for example, in oxygen reduction in proton exchange membrane fuel cells. Unlike main group dopants, a counter anion to the metal cation must be selected and this choice has hitherto received little attention for this synthesis method. Herein, we describe the profound effects that the anion has on the resultant iron/nitrogen-doped ordered mesoporous carbons (Fe-OMC). To increase the iron loading and the number of iron-centered catalytically active sites, we selected three iron salts Fe(OAc)2, Fe(OTf)2, and Fe(BF4)2·6H2O, which show greatly enhanced solubility in the liquid carbon precursor (furfurylamine) compared to FeCl3·6H2O. The increased solubility leads to a significantly higher iron loading in the Fe-OMC prepared with Fe(OTf)2, but the increase in performance as cathode catalysts in fuel cells is only marginal. The Fe-OMCs prepared with Fe(OAc)2 and Fe(BF4)2·6H2O exhibited similar or lower iron loadings compared to the Fe-OMC prepared with FeCl3·6H2O despite their much higher solubilities. Most importantly, the different iron salts affect not only the final iron loading, but also which type of iron species forms in the Fe-OMC with different types showing different catalytic activity.
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| 2. |
- Janson, Caroline, 1988, et al.
(författare)
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Improved Oxygen Reduction Activity of Transition Metal-Chelating Ordered Mesoporous Carbon Fuel Cell Catalysts by Milder Template Removal
- 2019
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Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 149:5, s. 1297-1304
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Tidskriftsartikel (refereegranskat)abstract
- In the synthesis of iron-chelating ordered mesoporous nitrogen-functionalized carbon (Fe–OMC) catalysts, the removal of the silica template is a crucial and critical step. The silica removal method used today for the Fe–OMCs is based on the very toxic hydrofluoric acid (HF), which usage should be limited where possible. Therefore, the aim of this study is to establish a mild (user-friendly), yet efficient, etch method based on dilute sodium hydroxide (NaOH), which does not impair the catalytic performance of the catalyst, to replace the currently used HF method. A comparison between catalysts etched with HF versus NaOH was performed in order to gain understanding how the two etch methods influence the final catalysts in terms of electrochemical, structural and catalytic properties. The NaOH etch was found to successfully remove the silica template, and interestingly, also improve the catalytic performance. The improved activity is explained by a carbon activation process occurring in the catalyst treated with the NaOH etch. With these findings, we show that it is possible to remove the silica in a more user-friendly way and simultaneously increase the catalysts’ performance by activation of the carbon. Graphical Abstract: [Figure not available: see fulltext.].
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| 3. |
- Janson, Caroline, 1988, et al.
(författare)
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Influence of iron precursor hydration state on performance of non-precious metal fuel cell catalysts
- 2018
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 6:7, s. 3116-3125
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Tidskriftsartikel (refereegranskat)abstract
- Iron ion-chelating ordered mesoporous carbon (Fe-OMC) catalysts are a class of non-precious metal catalysts for the oxygen reduction reaction in fuel cells. Here, the performance of Fe-OMC catalysts is studied in relation to variations in conditions employed during their synthesis. Specifically, we studied the effects of (i) the hydration state of the iron salt precursor, (ii) the aging time after mixing of the precursor solution and (iii) the relative amount of iron to N/C-precursor used during synthesis. The formation of complexes between the iron ion and the N/C-precursor was investigated by NMR spectroscopy and it was shown that a complex is formed with the amine group of the N/C-precursor being closest to the iron ion. All three parameters studied (i, ii, and iii) were found to have a significant impact on the complex formation between the iron ion and the N/C-precursor as well as on the performance of the resulting catalyst materials.
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| 4. |
- Janson, Caroline, 1988, et al.
(författare)
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Influence of Precursor Functional Groups on the Formation and Performance of Iron-Coordinating Ordered Mesoporous Carbons as Fuel Cell Catalysts
- 2017
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:40, s. 21827-21835
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Tidskriftsartikel (refereegranskat)abstract
- We examine the influence of precursor functional groups on the formation and electrocatalytic performance of iron ion-chelating ordered mesoporous carbon (Fe-OMC) fuel cell catalysts. First, we study whether the active sites in these catalysts consist of Fe-N-x or Fe-O-x chelates. To verify this, catalysts were prepared from two different molecular precursors (furfurylamine and furfuryl alcohol) and the functional groups' (-NH2 vs -OH) role in the formation of iron ion-chelating active sites in the catalysts was established. From electrochemical tests and EPR spectroscopy, conspicuously different behaviors were obtained for the catalyst prepared from furfurylamine compared to that prepared from furfuryl alcohol. It was unambiguously established that the amine group is central to the formation of electrocatalytically active sites in Fe-OMC catalysts and that these are of the Fe-N-x-OMC type. Additional Fe-OMC catalysts were prepared with the purpose to determine the influence of the two precursors on the formation of the carbon matrix. By complementing the furfurylamine with the more readily polymerizing furfuryl alcohol and using a mixture of the two as precursor solution in the synthesis, an overall improvement over the pure furfurylamine was achieved. The mixture gave a catalyst with, a larger pore volume and surface area, a higher conductivity, and a higher oxygen conversion rate.
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