Mass spectrometry

Mass spectrometry (MS) performs the analysis of compounds by ionising them and sepa- rating the generated ions according to the mass to charge ratio. [39] It allows the qualita- tive and quantitative determination of molecules with a variety of molecular masses, from small molecules such as O2to large organic molecules or proteins. [39] Every molecule has

a fragmentation pattern, which can be compared to a database and used as a fingerprint to identify unknown compounds. [39] In this work MS has been used to track the gases released upon TPD and to identify molecules in an organic mixture after separation by GC. The samples can be directly passed to the MS and ionised in an ionisation chamber. The resulting ions are then separated according to their mass to charge ratio by passage through a magnetic field, based on the Lorentz law and Newton’s second law. [39] The separated ions can then be detected and quantified. [39] Various different methods of ion- isation can be used. [39] Electron ionisation (EI) and electron spray ionisation (ESI) have been used in the utilised instruments.

2.3

References

[1] Paulus U.A., Schmidt T.J., Gasteiger H.A., Behm R.J. Oxygen reduction on a high-surface area Pt/Vulcan carbon catalyst: a thin-film rotating ring-disk electrode study. Journal of Electroanalytical Chemistry, 495(2), 134–145, January 2001. doi: 10.1016/S0022-0728(00)00407-1.

[2] Bard A.J., Faulkner L.R. Electrochemical Methods: Fundamentals and Applications. Wiley, New York, 2nd edition, December 2000. ISBN 978-0-471-04372-0.

[3] Qi Z. Electrochemical Methods for Catalyst Activity Evaluation. In J. Zhang, editor,

PEM Fuel Cell Electrocatalysts and Catalyst Layers, pages 547–607. Springer London,

[4] Schmidt T.J., Gasteiger H.A., St¨ab G.D., Urban P.M., Kolb D.M., et al. Char- acterization of High-Surface-Area Electrocatalysts Using a Rotating Disk Electrode Configuration. Journal of The Electrochemical Society, 145(7), 2354–2358, January 1998. doi:10.1149/1.1838642.

[5] Biddinger E.J., von Deak D., Singh D., Marsh H., Tan B., et al. Examination of Catalyst Loading Effects on the Selectivity of CNx and Pt/VC ORR Catalysts Using RRDE. Journal of The Electrochemical Society, 158(4), B402–B409, January 2011. doi:10.1149/1.3552944.

[6] Zhang L., Song C., Zhang J., Wang H., Wilkinson D.P. Temperature and pH De- pendence of Oxygen Reduction Catalyzed by Iron Fluoroporphyrin Adsorbed on a Graphite Electrode. Journal of The Electrochemical Society, 152(12), A2421–A2426, January 2005. doi:10.1149/1.2109667.

[7] Wu G., More K.L., Johnston C.M., Zelenay P. High-Performance Electrocatalysts for Oxygen Reduction Derived from Polyaniline, Iron, and Cobalt. Science, 332(6028), 443–447, April 2011. doi:10.1126/science.1200832.

[8] Chlistunoff J. RRDE and Voltammetric Study of ORR on Pyrolyzed Fe/Polyaniline Catalyst. On the Origins of Variable Tafel Slopes. The Journal of Physical Chemistry

C, 115(14), 6496–6507, April 2011. doi:10.1021/jp108350t.

[9] Bonnecaze R.T., Mano N., Nam B., Heller A. On the Behavior of the Porous Rotating Disk Electrode. Journal of The Electrochemical Society, 154(2), F44–F47, January 2007. doi:10.1149/1.2403082.

[10] Malko D. The oxygen reduction reaction (ORR) catalyzed by non precious metal/ni-

trogen/carbon composites. Master thesis, FAU Erlangen-N¨urnberg/Imperial College London, 2013.

[11] Shao M., editor. Electrocatalysis in Fuel Cells, volume 9 of Lecture Notes in Energy. Springer London, London, 2013. ISBN 978-1-4471-4910-1 978-1-4471-4911-8.

[12] Girault H.H. Analytical and Physical Electrochemistry. EPFL Press, Lausanne:New York, 1st edition, October 2004. ISBN 978-0-8247-5357-3.

[13] Lasia A. Electrochemical Impedance Spectroscopy and its Applications. Springer, New York, NY, June 2014. ISBN 978-1-4614-8932-0.

[14] Barsoukov E., Macdonald J.R., editors. Impedance Spectroscopy: Theory, Experi-

ment, and Applications. Wiley-Interscience, Hoboken, N.J, 2nd edition, March 2005.

ISBN 978-0-471-64749-2.

[15] van der Vliet D., Strmcnik D.S., Wang C., Stamenkovic V.R., Markovic N.M., et al. On the importance of correcting for the uncompensated Ohmic resistance in model experiments of the Oxygen Reduction Reaction. Journal of Electroanalytical Chem-

istry, 647(1), 29–34, August 2010. doi:10.1016/j.jelechem.2010.05.016.

[16] Boukamp B.A. A Linear Kronig-Kramers Transform Test for Immittance Data Val- idation. Journal of The Electrochemical Society, 142(6), 1885–1894, January 1995. doi:10.1149/1.2044210.

[17] Sch¨onleber M., Ivers-Tiff´ee E. Approximability of impedance spectra by RC elements and implications for impedance analysis. Electrochemistry Communications, 58, 15– 19, September 2015. doi:10.1016/j.elecom.2015.05.018.

[18] Sch¨onleber M., Klotz D., Ivers-Tiff´ee E. A Method for Improving the Robustness of linear Kramers-Kronig Validity Tests. Electrochimica Acta, 131, 20–27, June 2014. doi:10.1016/j.electacta.2014.01.034.

[19] Ecochemie Metrohm. Autolab Application Note EC07. http://www.ecochemie.nl/ download/Applicationnotes/Autolab_Application_Note_EC07.pdf. Accessed: 2016-10-16.

[20] Zhang J., editor. PEM Fuel Cell Electrocatalysts and Catalyst Layers: Fundamentals

and Applications. Springer, London, November 2008. ISBN 978-1-84800-935-6.

[21] Zhang H., Wang X., Zhang J., Zhang J. Conventional Catalyst Ink, Catalyst Layer and MEA Preparation. In J. Zhang, editor, PEM Fuel Cell Electrocatalysts and

Catalyst Layers, pages 889–916. Springer London, 2008. ISBN 978-1-84800-935-6

978-1-84800-936-3. doi:10.1007/978-1-84800-936-3 19.

[22] Langmuir I. THE CONSTITUTION AND FUNDAMENTAL PROPERTIES OF SOLIDS AND LIQUIDS. PART I. SOLIDS. Journal of the American Chemical Society, 38(11), 2221–2295, November 1916. doi:10.1021/ja02268a002.

[23] Brunauer S., Emmett P.H., Teller E. Adsorption of Gases in Multimolecular Layers.

Journal of the American Chemical Society, 60(2), 309–319, February 1938. doi: 10.1021/ja01269a023.

[24] Lowell S., Shields J.E., Thomas M.A., Thommes M. Characterization of Porous

Solids and Powders: Surface Area, Pore Size and Density. Springer Science & Busi-

ness Media, April 2006. ISBN 978-1-4020-2302-6.

[25] Barrett E.P., Joyner L.G., Halenda P.P. The Determination of Pore Volume and Area Distributions in Porous Substances. I. Computations from Nitrogen Isotherms.

Journal of the American Chemical Society, 73(1), 373–380, January 1951. doi:10.

1021/ja01145a126.

[26] Klockenk¨amper R., von Bohlen A. Total-Reflection X-Ray Fluorescence Analysis and

Related Methods. John Wiley & Sons, December 2014. ISBN 978-1-118-98587-8.

[27] Reimer L. Scanning Electron Microscopy: Physics of Image Formation and Micro-

analysis. Springer Science & Business Media, September 1998. ISBN 978-3-540-

63976-3.

[28] Williams D.B., Carter C.B. Transmission Electron Microscopy: A Textbook for Ma-

terials Science. Springer, 2nd edition, August 2009. ISBN 978-0-387-76502-0.

[29] Pennycook S.J., Nellist P.D., editors. Scanning Transmission Electron Microscopy:

Imaging and Analysis. Springer, March 2011. ISBN 978-1-4419-7199-9.

[30] Egerton R.F. Electron Energy-Loss Spectroscopy in the Electron Microscope. Springer Science & Business Media, 1996. ISBN 978-0-306-45223-9.

[31] Bell D.C., Garratt-Reed A.J. Energy Dispersive X-ray Analysis in the Electron Mi-

croscope. Garland Science, July 2003. ISBN 978-0-203-48342-8.

[32] van der Heide P. X-ray Photoelectron Spectroscopy: An introduction to Principles

and Practices. Wiley, Hoboken, N.J, 1st edition, December 2011. ISBN 978-1-118-

06253-1.

[33] Pels J.R., Kapteijn F., Moulijn J.A., Zhu Q., Thomas K.M. Evolution of nitrogen functionalities in carbonaceous materials during pyrolysis. Carbon, 33(11), 1641– 1653, January 1995. doi:10.1016/0008-6223(95)00154-6.

[34] Raki´c V., Damjanovi´c L. Temperature-Programmed Desorption (TPD) Methods. In A. Auroux, editor, Calorimetry and Thermal Methods in Catalysis, number 154 in Springer Series in Materials Science, pages 131–174. Springer Berlin Heidelberg, 2013. ISBN 978-3-642-11953-8 978-3-642-11954-5. doi:10.1007/978-3-642-11954-5 4. [35] Wertz J.E., Bolton J.R. Electron spin resonance: elementary theory and practical

applications. Chapman and Hall, 1986. ISBN 978-0-412-01161-0.

[36] Wikipedia. Electron paramagnetic resonance. https://en.wikipedia.org/wiki/ Electron_paramagnetic_resonance. Accessed: 2016-09-14.

[37] Fritz J.S., Gjerde D.T. Ion Chromatography. John Wiley & Sons, March 2009. ISBN 978-3-527-32052-3.

[38] McNair H.M., Miller J.M. Basic Gas Chromatography. Wiley-Interscience, Hoboken, N.J, 2nd edition, July 2009. ISBN 978-0-470-43954-8.

[39] de Hoffmann E., Stroobant V. Mass Spectrometry: Principles and Applications. Wiley-Interscience, 3rd edition, October 2007. ISBN 978-0-470-03311-1.

of 1,5-diaminonaphthalene in the presence of a metal salt and subsequent pyrolysis is a facile way to synthesise active ORR catalysts. The resulting materials are characterised and it is found that the microporous area seems to be important for a high ORR activity. The metal centre has a profound effect on the ORR activity and the electronic properties of the material as determined by EPR. Electron microscopy reveals atomic iron centres in the Fe-N/C material. The analysis suggests that the catalyst shares the same set of highly active sites as other high performing catalysts described in literature. This catalyst is therefore used as a model in order to study the active site in subsequent chapters.

Chapter 3

Synthesis and characterisation of

M-N/C catalysts

3.1

Introduction

Typical routes to the synthesis of highly active non-precious metal catalysts are discussed in Chapter 1. In short, a carbon support or a template is mixed with a metal source (typically iron) and a nitrogen source. This precursor mixture is heated under inert atmosphere at 700 to 1000 °C. [1–3] The resulting material is then leached by heating in acid. When a template is used, such as SiO2, the catalyst has to be leached with HF in

order to remove the template. [1–3] A second heat treatment has shown to increase the ORR activity. [1–3] If heated in ammonia gas the activity can be significantly increased, however at the expense of stability. [1–4] It has been speculated that this increase in

activity comes from the formation of axial ligands, improving electronic structure and proton transport capability of the active site. [1–4]

Although highly active catalysts have been synthesised, due to the complex composition in the precursor mixture, it has been challenging to establish structure property relation- ships. [1–4]

In this chapter a procedure is presented which allows the synthesis of a self-supporting catalyst. This means the need to include a carbon support or a templating agent is re- moved. The simplification of the synthesis allows identification of some structure property relationships. The material will be physically characterised by various techniques, with an emphasis on microstructure and the influence of a metal species on the properties of the material. It will be shown that this facile synthesis yields a catalyst which is similar and most likely contains the same types of active sites as other catalysts reported in the literature. Therefore, the study of the catalyst developed here in the subsequent chapters can be representative for most M-N/C catalysts, with a focus on atomic Fe-N/C sites. The chapter builds on result obtained during a preceding masters project, where the study of different precursors led to the discovery that the use of polymerised 1,5-diaminonaphthalene in combination with a metal as precursor will yield a high surface area material which does not require addition of carbon black as additive. [5] A general trend has been found that addition of Fe and Co beyond 1 wt% led to an increase of graphitization, which was detrimental for the activity. [5] Based on these results, the synthesis has been optimised and conditions varied to obtain structure property relationship.