Enhancement of polymer electrolyte fuel cell tolerance to CO by

Enhancement of polymer electrolyte
fuel cell tolerance to CO (by combination
of different mitigation methods)
HFCNordic 2013, Oslo 31.10-1.11.2013
Pauli Koski, Luis Perez Martinez, Taneli Rajala, Henri
Karimäki, Kaj Nikiforow, Timo Keränen and Jari Ihonen
VTT Technical Research Centre of Finland
5.7.2013
Overview
 VTT fuel cell research briefly
 HyCoRA – project introduction
 Motivation for research with low quality hydrogen
 CO impurity research with single cells
 Measurement system with on-line gas analysis
 The problem of oxygen contamination
 CO poisoning behavior as a function of fuel utilisation
 Summary and conclusions
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VTT Technical Research Centre of Finland
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5.7.2013
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VTT Fuel Cells
The main research areas today are
SOFC system research
SOFC stack development
HT-PEMFCs and methanol reforming
PEMFC systems and hydrogen quality
PEMFC materials and components
Enzyme catalysed & printed fuel cells
Electrochemical energy storage
Jari Kiviaho
Senior Principal Scientist
[email protected]
5.7.2013
PEMFC systems and hydrogen quality
The main focus is on PEMFC system
development and use of low grade
hydrogen in low temperature PEMFC
systems. The applications are industrial
working machines and utilisation of byproduct hydrogen from industry.
Jari Ihonen
Principal Scientist
[email protected]
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5.7.2013
Latest publication: Optimisation of air bleed
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Research with low quality hydrogen
- why and how?
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Why to do research with low quality hydrogen?
 Due to purification and quality assurance, automotive grade
hydrogen is several times more expensive than industry grade.
 Industrial hydrogen is available at refineries for peak, reserve and
regulation power production, that is essential with the growing
share of solar and wind power
 If system level mitigation measures are applied, vehicles in fleet
applications (single owner) could use much less expensive
hydrogen than automotive grade hydrogen (ISO 14687-2:2012),
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Operating PEMFC with low quality hydrogen
- practical issues and knowledge caps
 Hydrogen used in PEMFC is never 100% pure, but contains inert gases
as well as contaminants (CO being most important)
 The effect of inert gases and contaminants is dependent on (at least):
 The operation mode of the anode side
 Fuel utilisation per pass and total fuel utilisation
 Anode catalyst loading and type
 Temperature, pressure, humidity, anode stoichiometry
 Membrane thickness
 GDL gas transport properties
 Aging of the components
 Flow homogenity in the stack
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Open questions for automotive PEMFC research
 Which are the most relevant contaminants?
 What are most relevant anode Pt loadings?
 What should be the temperature, pressure and humidity?
 What is the most relevant duration of one measurement and what
should be the load profile?
 How to simulate change of gases (H2, O2, N2) between anode and
cathode in start and stop and shut-down of the automotive PEMFC?
 How to simulate the effect of aging, i.e. BoL performance vs. EoL?
 How to minimise the effects of test station, cross-contamination, GDL
aging?
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The main issue (?):
Operation of anode side (stoichiometric vs. dead-end)
 In automotive PEMFC system fuel efficiency is over 99% (in lab 50-80%)
 Inert gases as well as impurities can enrich over 100 times in anode loop
 In laboratory test station enrichment is 2-5 times
 In automotive PEMFC system N2 is enriched up to levels of 10-30 %, even higher
 Utilisation per pass (Uf) can be as low as 15-20% (vs. test station typical 80%)
 Linear flow velocities are different in labs and in automotive PEFC
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Measuring CO contamination
with exhaust gas analysis
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Setup for anode CO contaminant testing with
on-line exhaust gas analysis
C
A
CO
N2
• Dynamic contaminant mixing to
hydrogen feed allows wide range of COconcentrations to be used
Humid gas
feeds
Diluted CO
injection
μMFC
• Water is removed from the exhaust
sample gas with a membrane drier
GC
H2O sensor
Fuel Cell
• Analysis of the exhaust gas with a gas
chromatograph (GC)
Membrane dryer
• System built around Greenlight G60 test
station
Back pressure
regulation
To ventilation
H2 flow
meter
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Impurity injection control
0.05 sccm
MFC
Impurity
100 ppm
of CO
• Gas blend with known CO
concentration, balanced with N2
or H2
• Precision mass flow controller
(0.05-10 sccm) for impurity
blend
• Impurity is injected just before
the cell, minimising the time
delay and adsorption to surfaces
and dissolution to water
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To ventilation
200 sccm H2
3-way
solenoid
valve
25 ppb of CO
• A 3-way valve is used to flush air
traces from impurity feed line before
impurity injection
• The 3-way valve also allows precise
timing of the injection (as long as
volume between valve and H2 feed is
minimised)
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Description of GC and
exhaust gas preprocessing
• Low cost (< 35 k€) Agilent 6890N
equipped with methaniser and flame
ionisation detector (FID)
• With the current method, detection
limit is around 100 ppb with sample
analysis duration of 4.2 min
• GC does not tolerate water, therefore
water is removed from the exhaust
sample flow with a membrane dryer
Valve configuration
CO
CO2
• Membrane dryer has high selectivity
to water and low permeability for
other gases, including CO and CO2
Sample with 10 ppm of CO & CO2
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Measuring CO/CO2 –balance
and
the problem of the oxygen contamination
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Measuring CO/CO2 -balance – typical problems
 Ideally CO → CO2 conversion is the only source of CO2
 In reality, quite a few error sources exist:
• Fuel impurities (CO & CO2)
• Membrane cross-over (CO2)
• Carbon corrosion (CO2)
• Humidifier water (CO2)
• Air bleed impurities (CO & CO2)
 Some trace CO & CO2 also dissolved in liquid water
 Most of these can be eliminated or taken into account and subtracted from
the final values
 In addition, “oxygen contamination” (i.e. unintentional oxygen bleed) is an
issue. For example, oxygen content is about 15 mg/dm3 (0.46 mmol/dm3)
in water leaving municipal water treatment plant in Helsinki
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Unintentional oxygen bleed
 Some test station use water bleed to keep humidifiers clean
 1 dm3/h water bleed can introduce several ‰ of O2 in H2, when
typical 25 cm2 test cell is used. For 1 kW stack the O2
concentration can still be tens of ppm.
 Water of anode humidifier can be almost saturated with oxygen,
when experiments are started. This can cause high (several ‰)
levels of O2 in H2 in the beginning of the experiments.
 Humidifier refill water (which is evaporated to anode gas), can
keep the O2 concentration in H2 in level between sub ppm level
and few ppm.
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 The same conditions in all
experiments and clean (COfree) initial surface
 High CO level (6.1 ppm) and
0.3 mgPt/cm2
Cell voltage / V
Example of oxygen contamination
 The results show drastic effect
of oxygen contamination due
to initial oxygen in humidifier
water
CO / ppm
 65°C, 25 cm2 cell, 0.6 Acm-2
Time / h
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Mitigation of unintentional oxygen bleed
 Degas anode humidifiers (nitrogen purge at high temperature)
 Inactivate automatic water bleed, if included in the station
 Inactivate automatic water refill (if possible)
 Measure oxygen level in humidified hydrogen
 By-pass anode humidifier and use anode gas recirculation for the
humidification of the anode gas
 This solves the problem completely
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The effect of fuel utilization on the CO
contamination dynamics
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What is the importance of fuel utilisation per pass?
 Critical questions for CO poisoning dynamics in automotive
applications:
 Is contamination more dependent on CO concentration (in ppm) in
hydrogen or in total molar rate of CO (in mol/s)?
 When CO can be detected at the anode exit?
 How are these issues affected by the catalyst type, loading and
flow field structure?
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Experimental set-up for CO tolerance measurements
Membrane drier
– minimal CO
dissolving in water
Measurement of CO and CO2
at the anode exit
F, mass flow controller; B: bubbler, T: thermocouple, WT: water trap, D, dryer; R, rotameter;
RH, relative humidity probe; P, diaphragm pump and NV, needle valve.
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Summary of experimental conditions and materials
 Automotive conditions (353 K, 50% RH), but low pressure (1 bar at exit)
 Low Pt loading anodes (0.05 mgcm-2) for 25 cm2 cell with single channel
 CO levels simulate failures in ISO 14687-2:2012 quality control
 Fuel utilisation from 25% to 70% (automotive vs. labotarory)
 Air utilisation relatively low (40%), but reasonable when low pressure chosen
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Results of three ”standard measurements”
with 1 ppm CO and µf = 70 %
•
CO slips through immediately
•
Enrichment would start in
automotive PEMFC systems, since
hydrogen is recirculated.
•
CO concentration reaches initial 1
ppm after 30 minutes (30 mV
voltage drop)
•
Time scale for 50 mV voltage drop
is about 50 minutes
•
50% of CO (1.87*10-10 mol/s) is
slipping through the cell at this point
Performance of the fuel cell for µf = 70 % and 1 ppm CO feed (Experiment #1);
a) potential drop history, b) CO concentration at the anode outlet as a function of time and
c) estimated molar flow rate of CO at the anode outlet as a function of time. The CO is injected at t = 0 min.
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Results of constant CO concentration experiment
•
When CO molar flow is increased,
the response in the open anode cell
operation is almost the same.
•
50 mV cut-off voltage drop reached in
50, 55 and 60 minutes.
•
When CO molar flow is increased,
much more of the CO is slipped
through the cell.
•
In the real system with recirculation,
the response should be different, as
CO would accumulate in the system!
Performance of the fuel cell for µf = 70 % (experiment #1), µf = 40 % (#2) and µf = 25 % (#3) and 1 ppm CO feed:
a) potential drop history, b) CO concentration at the anode outlet as a function of time and
c) estimated molar flow rate of CO at the anode outlet as a function of time.
The Y axis on the right of Figure 4c is the corresponding molar flow rate of CO at the anode inlet. The CO is injected at t = 0 min.
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Results of constant CO molar rate experiment
•
When H2 molar flow is increased (and
CO in ppm decreased), the poisoning
rate is decreased.
•
50 mV cut-off voltage drop reached in
30, 70 and 145 minutes for 1, 0.57 and
0.36 ppm.
•
When H2 molar flow is increased, more
of the CO is slipped through the cell.
•
Enrichment of CO (in ppm) is most clear
for the lowest H2 molar flow, but lowest
amount (in mol/s) slipped through.
Performance of the fuel cell for µf = 70 % (experiment #4), µf = 40 % (#5) and µf = 25 % (#6)
a) potential drop history, b) CO concentration at the anode outlet as a function of time; and
c) estimated molar flow rate of CO at the anode outlet as a function of time.
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What is the importance of fuel utilisation per pass?
 Is contamination more dependent on CO concentration (in ppm) in
hydrogen or in total molar rate of CO (in mol/s)
 YES, but estimation of the effect is difficult using open
anode data and single cells
 When CO can be detected at the anode exit?
 Immediately after it has been fed in the cell. However, this
slip rate is dependent on number of parameters.
 How are these issues affected by the catalyst type, loading and
flow field structure?
 A very good question, which must be studied for
determining the right CO level in ISO 14687-2:2012
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Test station equipped to mimic an automotive system
Moving to PEFC
system level
Miniature automotive system
Passive humidification through cathode
Dead end with recirculation
Custom purge triggering routines
Enrichment and control of nitrogen in anode loop
Impurity injection with constant flow rate
Flow rate measurement using H2/RH% sensor
Both open anode and recirculation modes
Enrichment and control of nitrogen in anode loop
Stoichiometric modes in dead-end operation for impurity feeding
Flow rate measurement using H2/RH% sensor
Experience from real PEFC systems essential
Humid gas
feeds
C
CO
N2
•
•
•
•
•
•
•
•
•
•
•
Diluted CO
injection
A
μMFC
SV
P
H2
FM
SV
H2 flow
meter
Load
HC
H,T
HC
H,T
PR
PEMFC stack
H,T
Air
H,T
F
H2
sensor
FM
MH
P
FM
Fuel Cell
T
T
P
DF
Tap
water
H2O
sensor
H,T
FM
Recirculation
pump
Membrane dryer
FM
Back pressure
regulation
SV
HE
To ventilation
H2 flow
meter
GC
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Moving to PEFC
system level
• Inert gases affect the dynamics of
mass transport (instability)
• How does CO impact depend on
this and what is the combined
effect?
2 ppm CO
→ Next step is to construct a 1-2 kW
system with on-line gas analysis
suited for benchmarking CO
mitigation methods and operation
strategies for low quality hydrogen
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Recommendations for automotive PEMFC research 1
 Exit/recirculation loop gas analysis should always be applied
 Measurements with recirculation of anode gas should be preferred over
open anode measurements
 If open anode measurements are used, degassing of anode humidifier
water (CO2, O2 removal) and control of MQ water is necessary
 In anode gas recirculation system this is avoided
 Quality of used hydrogen and air should be frequently controlled
 Cell level measurements should be verified with stack level
measurements with relevant fuel utilisation per pass
 Catalyst active area should be measured BoL and EoL
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Recommendations for automotive PEMFC research 2
 Measurements should be done with sufficiently wide temperature,
pressure and humidity range
 The effect of anode catalyst loading should be studied whenever possible
 The aging (thinning) of the membrane should be taken into account
 Increased gas permeability increase internal air bleed
 Measurement durations should be similar to typical use of automotive
PEMFC systems
 Exchange of gases should be comparable to automotive PEMFC systems
 Measurement during shut-down, if system test bench is used
HyCoRA
Hydrogen Contaminant Risk Assessment
NON-CONFIDENTIAL VERSION
Jari Ihonen
1.11.2013
VTT Technical Research Centre of Finland
5.7.2013
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Project summary for HyCoRA
 In FCH JU 2013 call a VTT-lead consortium submitted a project
proposal to the topic SP1-JTI-FCH.2013.1.5 (Fuel quality assurance for
hydrogen refuelling stations).
 The proposal passed all the thresholds in the expert evaluation
 HyCoRA was invited to negotiation meetings, which are ongoing
 In order to minimize the time delay HyCoRA consortium is already now
informing OEMs for the possibility of joining the advisory board.
 Due to negotiations, there can be some changes in the project plan
presented in this document.
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Project consortium and budget
 Overall budget is about 4.2 M€ with maximum of 2.16 M€ FCH JU
contribution
 Research partners are:
 VTT (coordinator &WP4
leader)
 CEA (WP1 leader)
 SINTEF (WP2&WP3
leader)
 JRC (WP5 leader)
 Industry partners are:
 Powercell Sweden AB
 Protea Ltd
Since there are no automotive OEMs or hydrogen refuelling station
producers/operators in the consortium, the advisory board is open for all
companies in these categories.
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SP1-JTI-FCH.2013.1.5:
Fuel quality assurance for hydrogen refuelling stations
 Overall project objective / Scope of Work
 The overall objective is to reduce cost of hydrogen fuel quality
assurance (QA) for (Hydrogen Refuelling Station) HRSs
 Expected Outcome
 Cheaper and more reliable fuel quality assurance procedures and
instrumentation for HRSs
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The main objectives for Topic 1.5
 Establishing a simplified and diversified set of requirements for
hydrogen fuel quality depending on fuel feedstock and production
technologies (biogas, reforming, electrolysis, by-product etc.)
 Simplifying fuel quality control by enhance knowledge of
correlations between gas impurity concentrations based on
extensive in field measurements at HRS fuel nozzle
 Assessing ways to reduce the number of analysis methods
required for complete QA
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HyCoRA strategy– Risk Assessment
 In HyCoRA project quantitative risk assessment is applied to optimise the needs
for the QA with existing (draft) ISO standard
 Risk assessment provides information for the required frequency and accuracy
for the gas analysis at the nozzle and/or in production
 Risk assessment gives the right focus for development of the new analytical
methodology for the gas analysis
 Risk assessment requires information at least from:
 a) the real susceptibility for various poisonous species specifically for
automotive applications – automotive FC system data needed
 b) probabilities for QA failure in hydrogen production site and/or at HRS – data
for gas analysis methods needed
 c) concentration correlations between contaminant species in fuel - impurity
concentrations at production sites and HRS nozzle needed
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Acknowledged sources and co-authors for literature review
and experimental results
 Articles
 Nikiforow, K., Karimäki, H., Keränen, T.M., Ihonen, J. Optimization study of purge cycle in proton
exchange membrane fuel cell system (2013) Journal of Power Sources, 238, pp. 336-344.
 Karimäki, H., Pérez, L.C., Nikiforow, K., Keränen, T.M., Viitakangas, J., Ihonen, J. The use of online hydrogen sensor for studying inert gas effects and nitrogen crossover in PEMFC system
(2011) International Journal of Hydrogen Energy, 36 (16), pp. 10179-10187.
 Luis C. Pérez, Pauli Koski, Jari Ihonen, José M. Sousa, Adélio Mendes Effect of fuel utilization on
the carbon monoxide poisoning dynamics of PEMFC, Submitted to the Journal of Power Sources
 Thesis
 Rajala, Taneli Enhancement of polymer electrolyte fuel cell tolerance to CO by combination of
different mitigation methods, Master’s thesis, University of Helsinki (2013)
 Nikiforow, Kaj Optimization of polymer electrolyte membrane fuel cell systems – Applied study of
hydrogen recirculation, Master’s thesis, Aalto University
 Project reports:
 Literature reports in FCH JU HyQ project (grant agreement n° 256773) Jari Ihonen (VTT) and
Pierre-André Jacques (CEA)
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Acknowledgements for funding
 The work leading to these results has received funding from the
European Union's Seventh Framework Programme (FP7/20072013) under grant agreement n° 256773.
 This research has been conducted under the “Fuel Cell 20072013” technology program of Tekes, the Finnish Funding Agency
for Technology and Innovation. The authors would also like to
acknowledge their TopDrive and DuraDemo project partners.
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VTT creates business from technology
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