Electrochemical characterization of direct alcohol fuel cells using in-situ differential electrochemical mass spectrometry [Elektronische Ressource] / Vineet Rao

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Informations

• Publié par: technische_universitat_munchen
• Publié le: 01 janvier 2008
• Nombre de lectures: 34
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

PHYSIK-DEPARTMENT



Electrochemical Characterization of Direct
Alcohol Fuel Cells using in-situ Differential
Electrochemical Mass Spectrometry

Dissertation
von

M. Sc. (Integ) Vineet Rao


TECHNISCHE UNIVERSITÄT
MÜNCHEN
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Energy Conversion



Technische Universität München
Fakultät für Physik
Lehrstuhl für Grenzflächen und Energieumwandlung E19


Electrochemical Characterization of Direct Alcohol Fuel Cells
using in-situ Differential Electrochemical Mass Spectrometry



Vineet Rao


Vollständiger Abdruck der von der Fakultät für Physik der Technischen Universität München
zur Erlangung des akademischen Grades eines

Doktors der Naturwissenschaften (Dr. rer. nat.)

genehmigten Dissertation.

Vorsitzender: Univ.-Prof. Dr. J. L. van Hemmen

Prüfer der Dissertation:
1. Univ.-Prof. Dr. U. Stimming
2. Univ.-Prof. Dr. J. Barth

Die Dissertation wurde am 15.02.2008 bei der Technischen Universität München eingereicht
und durch die Fakultät für Physik am 09.06.2008 angenommen.



2
Table of contents

Abstract..................................................................................................................................... 6
Zusammenfassung.................................................................................................................... 7
1. Introduction.......... 9
1.1 Direct methanol fuel cell............................................................................................................. 9
1.1.1 PEMFCs and DMFCs: A comparison ................................................................................................ 10
1.1.2 Kinetic limitations .............................................................................................................................. 11
1.1.3 Methanol and water crossover............................................................................................................ 12
1.1.4 Anode electrocatalyst limitations........................................................................................................ 13
1.2 Electrocatalysis of methanol oxidation.................................................................................... 14
1.2.1 The methanol system.................... 14
1.2.2 Methanol adsorption........................................................................................................................... 15
1.2.3 Methanol oxidation products .............................................................................................................. 16
1.3 Introduction to DEMS.............................................................................................................. 18
1.3.1 Differential Electrochemical Mass Spectrometry (DEMS) system .................................................... 18
1.3.2 FC -DEMS systems with liquid and gas anode feeds ........................................................................ 19
1.4 Characteristics of DMFC anode electrocatalyst..................................................................... 19
1.4.1 Catalyst morphology........................................................................................................................... 20
1.4.2 Particle size effects ............................................................................................................................. 21
1.4.3 Inherent mismatch between nafion micelle and carbon support particles .......................................... 21
1.4.4 Introduction to sibunit carbons as catalyst support............................................................................. 23
1.4.5 Investigating the effect of carbon support porosity on catalytic activity ............................................ 24
1.5 Ethanol electrocatalysis ............................................................................................................ 26
1.5.1 Acidic medium ................................................................................................................................... 27
1.5.2 Alkaline medium ................................................................................................................................ 28
2. Experimental....................................................................................................................... 30
2.1 Membrane electrode assembly.................................................................................................30
2.2 Experimental setup ................................................................................................................... 30
2.3 Calibration of FC-DEMS system............................................................................................. 31
2.3.1 CO stripping for calibration and related problems.............................................................................. 31
2.3.2 Potentiostatic bulk CO oxidation for calibration ................................................................................ 34
2.4 Description of electrochemical cell setup ................................................................................ 36
3. Characterization of anode in a direct methanol fuel cell................................................ 38
3
3.1 DMFC anode catalyst layer properties ................................................................................... 38
3.1.1 Measurement of electrochemically active area by CO stripping ........................................................ 38
3.1.2 Measurement ofically active area by MeOH stripping ................................................ 39 ad
3.1.3 Measurement of methanol oxidation current ...................................................................................... 41
3.1.4 Simplistic catalyst layer model........................................................................................................... 43
3.1.5 Checking validity of the solutions provided by CL model ................................................................. 49
3.1.6 Results obtained from catalyst layer model........................................................................................ 51
3.2 Measurement for activity of PtRu/Sibunit catalyst series ..................................................... 54
3.2.1 Experimental....................................................................................................................................... 54
3.2.1.1 Catalyst preparation .................................................................................................................... 54
3.2.1.2 Characterization of the sibunit carbon supports.......................................................................... 54
3.2.1.3 Electrochemical measurements................................................................................................... 57
3.2.2 Results and Discussion.................... 57
3.2.2.1 Catalyst characterization............................................................................................................. 57
3.2.2.2 Optimization of the Nafion ® content in MEAs.......................................................................... 60
3.2.2.3 Metal utilization in PtRu/C electrocatalysts................................................................................ 62
3.2.2.4 Methanol oxidation..................................................................................................................... 64
23.2.2.5 Mass activity at higher catalyst loading(>0.3mg/cm )................................................................ 68
3.2.2.6 Oxygen reduction........................................................................................................................ 70
3.2.2.7 Investigation of the sibunit sample series in electrochemical cell .............................................. 75
4. In-situ DEMS studies on direct C2-alcohol fuel cells...................................................... 78
4.1 DEMS on ethanol oxidation and ethylene glycol oxidation in acidic membranes............... 78
4.1.1 Experimental strategies....................................................................................................................... 78
4.1.2 Experimental Results..................................................................................................... 80
4.1.2.1 CO current efficiency as a function of potential and temperature ............................................. 80 2
4.1.2.2 CO current efficiency a