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The Impact of Hydrocarbon and Carbon Oxide Impuritiesin the Hydrogen Feed of a PEM Fuel Cell
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.ORCID iD: 0000-0002-6019-6485
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The proton exchange membrane fuel cell generates electricity from hydrogen and oxygen (from air) through electrocatalytic reactions in an electrochemical cell. The Pt/C catalyst, commonly used in PEM fuel cells, is very sensitive to impurities that can interact with the active catalyst sites and limit fuel cell performance. Unfortunately, most hydrogen is currently produced from fossil sources, and inevitably contains impurities.

The subject of this thesis is the effect of hydrogen impurities on the operation of a PEM fuel cell using a Pt/C anode. The impurities studied are carbon monoxide (CO), carbon dioxide (CO2), and selected hydrocarbons. Particular focus is given to the interaction between the impurities studied and the anode catalyst. The main method used in the study involved performing cyclic voltammetry and mass spectrometry, simultaneously. Other electrochemical techniques are also employed.

The results show that all the impurities studied adsorb to some extent on the Pt/C catalyst surface, and require potentials comparable to that of CO oxidation, i.e., about 0.6V, or higher to be removed by oxidation to CO2. For complete oxidation of propene, and toluene, potentials of above 0.8, and 1.0V, respectively, are required. The unsaturated hydrocarbons can be desorbed to some extent by reduction, but oxidation is required for complete removal. Adsorption of ethene, propene, and CO2 is dependent on the presence of adsorbed or gaseous hydrogen. Hydrogen inhibits ethene and propene adsorption, but facilitates CO2 adsorption. Adsorption of methane and propane is very limited and high concentrations of methane cause dilution effects only.

The adlayer formed on the Pt/C anode catalyst in the presence of CO2, or moderate amounts of hydrocarbons, is found to be insffuciently complete to notably interfere with the hydrogen oxidation reaction. Higher concentrations of toluene do, however, limit the reaction.

Abstract [sv]

Polymerelektrolytbränslecellen genererar elektricitet fran vätgas och syrgas (fran luft) genom elektrokatalytiska reaktioner i en elektrokemisk cell. Den platina-baserade katalysator som oftast används i dessa bränsleceller är känslig mot föroreningar, då dessa kan interagera med katalysatorns aktiva yta, och därmed begränsna bränslecellens prestanda. Tyvärr produceras dagens vätgas huvudsakligen fran fossila källor och innehåller därför oundvikligen föroreningar.

Denna avhandling behandlar hur olika vätgasföroreningar påverkar katalysatorns aktivitet och bränslecellens drift. De föroreningar som studeras är kolmonoxid (CO) och koldioxid (CO2), samt ett antal mindre kolväten. Störst fokus ligger på hur dessa föroreningar interagerar med anodens Pt/C katalysator. Den metod som huvudsakligen används är cyklisk voltammetri kombinerat med masspektrometri, men flera elektrokemiska metoder har använts.

Resultaten visar att alla undersökta föroreningar adsorberar på Pt/C katalysatorns yta i större eller mindre utstreckning. For att avlägsna det adsoberade skiktet genom oxidation till CO2 krävs potentialer jämförbara med CO oxidation, dvs ca 0,6V, eller högre. Fullständig oxidation av propen eller toluen kräver potentialer högre än 0,8V respektive 1,0V. De omättade kolvätena kan delvis avlägsnas genom reduktion, men fullständig avlägsning kräver oxidation. Närvaron av väte, i gasform eller adsorberat pa katalysatorn, hämmar adsorptionen av eten och propen, men främjar CO2 adsorption. Metan och propan adsorberar i mycket begränsad utstreckning på Pt/C katalysatorns yta. De prestandaförluster som uppstår av höga koncentrationer av metan förklaras av utspädning av vätgasen.

Det adsorberade skiktet som bildas när Pt/C katalysatorn exponeras för CO2 eller måttliga koncentrationer av studerade kolväten, är inte tillräckligt heltäckande for att märkbart påverka vätgasreduktionen. Däremot kan höga koncentrationer av toluen begränsa reaktionen.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , 91 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2016:26
Keyword [en]
Fuel Cell, Hydrogen Impurities, Carbon Monoxide, Carbon Dioxide, Ethene, Propene, Methane, Propane, Toluene, Electrochemically Active Surface Area, Cyclic Voltammetry, Mass Spectrometry
Keyword [sv]
bränslecell, vätgasföroreningar, kolmonoxid, koldioxid, eten, propen, metan, propan, toluen, elektrokemisk aktiv yta, cyklisk voltammetri, masspektrometri
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-193694ISBN: 978-91-7729-008-7 (print)OAI: oai:DiVA.org:kth-193694DiVA: diva2:1033659
Public defence
2016-10-28, K2, Teknikringen 28, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20161010

Available from: 2016-10-10 Created: 2016-10-07 Last updated: 2016-10-10Bibliographically approved
List of papers
1. Active Area Determination of Porous Pt Electrodes Used in Polymer Electrolyte Fuel Cells: Temperature and Humidity Effects
Open this publication in new window or tab >>Active Area Determination of Porous Pt Electrodes Used in Polymer Electrolyte Fuel Cells: Temperature and Humidity Effects
Show others...
2010 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, Vol. 157, no 12, B1795-B1801 p.Article in journal (Refereed) Published
Abstract [en]

This paper discusses the proper measure of the electrochemically active area (ECA)of carbon supported Pt catalyst in PEM fuel cells employing in situ cyclic voltammetry. The charges of the hydrogen underpotential deposition (Hupd) and CO stripping peak obtained in situ are compared, and the influence of operation temperature (25–80°C) and relative humidity (40%–90%) is discussed. The results show that the charges of the Hupd decrease with rising temperature, while the corresponding charges of the CO stripping peak are essentially independent of temperature, at least at high relative humidity. The unexpectedly small Hupd charges are explained by the significant overlap with the hydrogen evolution reaction in a fuel cell at elevated temperatures. According to our results, it is proposed that a more reliable value of Pt ECA is estimated from the CO stripping charge. However, with decreasing humidity the charges of both Hupd and CO stripping peaks decrease, which is probably an effect of increasing blockage of Pt active sites by hydrophobic domains in the electrode ionomer. Some implications of varying cell conditions on the estimated Pt ECA and its correlation with fuel cell activity are discussed in an example from a fuel cell degradation test.

Keyword
SINGLE-CRYSTAL SURFACES, CARBON-MONOXIDE, UNDERPOTENTIAL DEPOSITION, HYDROGEN ADSORPTION, MEMBRANE INTERFACE, PT(100) ELECTRODES, AQUEOUS H2SO4, CO OXIDATION, PLATINUM, ELECTROOXIDATION
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-25266 (URN)10.1149/1.3494220 (DOI)000283938300022 ()2-s2.0-78449298256 (Scopus ID)
Funder
StandUp
Note

QC 20101014. Tidigare titel: Active Area Determination of Porous Pt Electrodes Used inPEM Fuel Cells: Temperature and Humidity Effects

Available from: 2010-10-14 Created: 2010-10-14 Last updated: 2016-10-07Bibliographically approved
2. Influence of Hydrogen and Operation Conditions on CO2 Adsorption on Pt and PtRu Catalyst in a PEMFC
Open this publication in new window or tab >>Influence of Hydrogen and Operation Conditions on CO2 Adsorption on Pt and PtRu Catalyst in a PEMFC
2013 (English)In: ECS Electrochemistry Letters, ISSN 2162-8726, Vol. 2, no 5, F41-F43 p.Article in journal (Refereed) Published
Abstract [en]

CO2 is a major component in reformate gas and can, as a source of CO, be a catalyst poison in polymer electrolyte membrane fuel cells. The effect of CO2 on cell performance is not fully understood in the presence of hydrogen. This paper addresses the influence of hydrogen on CO2 adsorption on Pt/C and PtRu/C catalysts. The results show that the reduction and adsorption of CO2 is slow but increases if hydrogen is present, especially on PtRu/C. Further, exposure to a CO2 and H-2 mixture at 0.15 V on PtRu/C results in current oscillations, which are dependent on operation conditions.

Keyword
Membrane Fuel-Cells, Gas Shift Reaction, Carbon-Dioxide, Oxidation, Monoxide, Anode, Electrocatalysts, Oscillations, Spectroscopy, Performance
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-123638 (URN)10.1149/2.008305eel (DOI)000318556600007 ()2-s2.0-84880445075 (Scopus ID)
Funder
StandUp
Note

QC 20150626

Available from: 2013-06-18 Created: 2013-06-13 Last updated: 2016-10-07Bibliographically approved
3. Influence of toluene contamination at the hydrogen Pt/C anode in a proton exchange membrane fuel cell
Open this publication in new window or tab >>Influence of toluene contamination at the hydrogen Pt/C anode in a proton exchange membrane fuel cell
2010 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 55, no 26, 7643-7651 p.Article in journal (Refereed) Published
Abstract [en]

For fuel cells run on hydrogen reformate, traces of hydrocarbon contaminants in the hydrogen gas may be a concern for the performance and lifetime of the fuel cell. This study focuses on the influence of low concentrations of toluene on the adsorption and deactivation chemistry in a proton exchange membrane (PEM) fuel cell. For this purpose cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques were employed. Results from adsorption and desorption (by oxidation or reduction) experiments performed in a humidified nitrogen or hydrogen flow in a fuel cell test cell with a mass spectrometer system connected to the outlet are presented. The influence of adsorption potential, temperature, and humidity are discussed. The results show that toluene adsorbs on the catalyst surface in a broad potential window, up to at least 0.85 V versus RHE at 80 degrees C. Adsorbed toluene oxidizes to CO2 with peak potentials above 1.0V for temperatures below 95 degrees C. Some desorption of toluene (or reduced products) may take place at potentials below 0V. In a hydrogen flow, toluene contamination in per mille concentrations leads to a continuous growth of the charge transfer resistance, while a 10-fold dilution of the toluene concentration resulted in a low and constant charge transfer resistance even for longer exposures. This indicates that a competition between toluene and hydrogen may take place on the active platinum surface at the anode.

Keyword
Toluene contamination, PEMFC, Anode, Cyclic voltammetry, Electrochemical impedance spectroscopy
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-29193 (URN)10.1016/j.electacta.2009.11.048 (DOI)000283209800015 ()2-s2.0-77957109684 (Scopus ID)
Note
QC 20110201Available from: 2011-02-01 Created: 2011-01-27 Last updated: 2017-12-11Bibliographically approved
4. The influence of ethene impurities in the gas feed of a PEM fuel cell
Open this publication in new window or tab >>The influence of ethene impurities in the gas feed of a PEM fuel cell
2013 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 38, no 1, 497-509 p.Article in journal (Refereed) Published
Abstract [en]

Hydrogen produced by reforming may contain traces of hydrocarbon contaminants. These traces may affect the performance and lifetime of a fuel cell run on reformate-hydrogen. This study treats the influence of low concentrations of ethene on the adsorption and deactivation chemistry in a polymer electrolyte membrane (PEM) fuel cell. The study employs mainly cyclic voltammetry accompanied with an on-line mass spectrometer to analyse the outlet gas. Results from adsorption and desorption, by either oxidation or reduction, are presented, and the influence of adsorption potential, temperature and humidity and the presence of hydrogen are discussed. The results show that the adsorption of traces of ethene in a fuel cell is highly dependent on adsorption potential and that ethene adsorbs on Pt catalyst in a limited potential window only. Ethene cannot displace adsorbed H and is oxidised already at potentials of 0.6 V versus RHE at 80°C, where the only detectable product is CO 2. A considerable part of ethene adsorbed at potentials above the hydrogen adsorption/desorption region can be reduced at low potentials and is desorbed as methane or ethene. Overall, the effect of low concentrations of ethene in the hydrogen feed on fuel cell performance is minimal, and no significant loss in cell voltage is found when ethene contaminated hydrogen is fed to a fuel cell running on hydrogen and oxygen at a constant load at 80°C and at highly humidified conditions.

Keyword
Ethene, Impurity, Mass spectrometry, PEM fuel cell, Pt/C, Stripping voltammetry
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-118214 (URN)10.1016/j.ijhydene.2012.06.119 (DOI)000315001500056 ()2-s2.0-84871980167 (Scopus ID)
Funder
Swedish Research CouncilStandUp
Note

QC 20130213

Available from: 2013-02-13 Created: 2013-02-13 Last updated: 2017-12-06Bibliographically approved
5. Reformate Hydrogen Fuel in PEM Fuel Cells: the Effect of Alkene Impurities on Anode Activity
Open this publication in new window or tab >>Reformate Hydrogen Fuel in PEM Fuel Cells: the Effect of Alkene Impurities on Anode Activity
2013 (English)In: ECS Transactions, Electrochemical Society, 2013, 1857-1865 p.Conference paper, Published paper (Refereed)
Abstract [en]

Reformate hydrogen contains many impurities, some are well known while others have been less studied. Hydrocarbons are possible impurities in reformate hydrogen and are among those less studied. This study if aimed at alkenes, with special focus on propene. Adsorption and desorption on the Pt catalyst is studied using stripping cyclic voltammetry combined with mass spectrometry. The results show that although the effect of propene in the presence of hydrogen is expected to be minimal, adsorption and blockage of catalytic sites cannot be ruled out. A small amount of ad-species is formed on Pt at low adsorption potentials, and in the presence of hydrogen, although suppression of the hydrogen desorption peak was minimal if hydrogen was adsorbed on the Pt catalyst prior to exposure.

Place, publisher, year, edition, pages
Electrochemical Society, 2013
Series
ECS Transactions, ISSN 1938-5862 ; 58
Keyword
Adsorption, Catalyst supports, Cyclic voltammetry, Desorption, Hydrocarbons, Mass spectrometry, Platinum, Propylene, Proton exchange membrane fuel cells (PEMFC)
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-138885 (URN)10.1149/05801.1857ecst (DOI)000354475600184 ()2-s2.0-84905008227 (Scopus ID)
Conference
224th ECS Meeting, October 27 – November 1, 2013, San Francisco, California
Funder
StandUp
Note

QC 20140214

Available from: 2013-12-20 Created: 2013-12-20 Last updated: 2016-10-07Bibliographically approved
6. The Effect of Hydrocarbon Impurities in the Hydrogen Fuel on the Anode Activity in PEMFC
Open this publication in new window or tab >>The Effect of Hydrocarbon Impurities in the Hydrogen Fuel on the Anode Activity in PEMFC
Show others...
2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The reformate fuel cell has recently gained increasing attention both for APUs in vehicles

operating on diesel and in stationary applications such as micro-CHP operating on natural

or biogas. In addition to hydrogen gas, reformate contain considerable amounts of CO2,

nitrogen, water vapour and traces of CO, sulphur species and hydrocarbons. CO and H2S

are well known poisons to the anode [1] but the influence of hydrocarbon species in the

fuel cell has not been much investigated. We have previously investigated toluene [2] and

ethene [3] on the anode Pt/C catalyst in the PEM fuel cell. In this paper we will discuss the

influences of alkenes and alkanes in the light of some novel results on the effect of

propene, propane and methane in the PEM fuel cell. We have especially focused on the

adsorption and deactivation phenomena of low concentrations of contaminant on a Pt/C

catalyst. In the experiments, in situ stripping voltammetry and on-line mass spectrometer

were employed. The effects of adsorption potential and temperature are discussed. We

show that propene is more poisonous to the Pt/C catalyst than ethene as it is adsorbed on

the catalyst surface within the Hupd region and forms an adlayer that can be oxidized in two

steps between 0.5-1 V (at 80°C, 90%RH) or be hydrogenated to propane in the Hupd region

and in the presence of hydrogen.

National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-138863 (URN)
Conference
Proceeding paper 4th European PEFC and H2 Forum, Luzern, Switzerland, 2-5 July 2013
Funder
StandUp
Note

QC 20140826

Available from: 2013-12-20 Created: 2013-12-20 Last updated: 2016-10-07Bibliographically approved

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