Impact of air pollutants on PEM fuel cells · Conditioning Contamination Recovery EIS Cleaning CV CV CV RAP 1 hour without contaminant 1 hour with contaminant 1 hour without contaminant

Zentrum für BrennstoffzellenTechnik GmbH

Tests with single cell

Dipl.-Ing. Ulrich Misz

Statusworkshop ALASKA

Duisburg, 28.01.2016

Impact of air pollutants on PEM fuel cells

© by ZBT – all rights reserved. Confidential – no passing on to third parties 2

Content

� Basics test bench, single cell and operating conditions

� Harmful gas screening

– influence of temperature, potential and harmful gas concentration

– SO2, NH3, C7H8 ,C2H6, NO, NO2

� Influence of humidity

– NH3, NO and NO2

� Long term test with SO2

– influence of NO during measurements with SO2

– accumulation of SO2

� Realistic NOx concentrations and limit values

– „unintended“ influence of NOx

– limit values and possibility of regeneration

a) with contaminated air

b) with clean air

� Summary


Content




– SO2, NH3, C7H8 ,C2H6, NO, NO2


– NH3, NO and NO2








b) with clean air

� Summary


Basics test bench

� Automated 24/7 cyclic operation (voltage or current controlled)

� Pressurized operation

� Dynamic humidity control (0-100%)

� Dynamic metering of contaminants and contaminant mixtures (ppb, ppm, %)

� Automated CV and EIS measurements


Single cell and operating conditions

� Single cell

– hardware by Automotive Fuel Cell Cooperation (AFCC)

– straight flow field with high stoichiometric rates provides near-zero gradient conditions (iso-thermal, iso-baric, iso-potential)

– MEA with loading of 0.4 (0.25) mg cm-2 Pt/C on cathode and 0.1 (0.05) mg cm-2 Pt/C + … on anode

– active area 45.15 cm²

� Operating conditions

– constant flow rates of 12 l min-1 pressurized air at cathode and 2 l min-1 H2 at anode

– pressure of 2.5 barabs at cathode and 2.7 barabs at anode

– humidification of 100 % at anode and cathode (except experiments with humidity variation)


Content




– SO2, NH3, C7H8 ,C2H6, NO, NO2


– NH3, NO and NO2








b) with clean air

� Summary


Harmful gas screening Test procedure

� Investigation of 27 different operating points

� Variation of temperature, potential and harmful gas concentration

� Electrochemical analyzes and U-I-characterization after each operating point

Concentration 1 Concentration 2 Concentration 3

87°C43°C70°C0.85 V 0.85 V0.85 V

0.7 V 0.7 V 0.7 V

0.55 V 0.55 V0.55 V

t

E

Conditioning Contamination Recovery EIS Cleaning CV CV CV RAP

1 hour without

contaminant

1 hour with

contaminant

1 hour without

contaminant

with N2

at 450 mV

0.1 – 1 V

4x

at 100 mV s-1

0.1 – 0.865 V

4x

at 100 mV s-1

0.1 – 0.865 V

2x

at 100 mV s-1

2.2 A cm-2

1.7 A cm-2

1.0 A cm-2

0.1 A cm-2

t

I

Variation of:

C

T

E

0.85 V


Harmful gas screening SO2

� No influence within one hour under contamination with 100 ppb SO2 in air

� Contamination with 1 ppm and 4 ppm in air result in strong current drops

� Current loss up to 95% within one hour, slightly lower degradation at elevated temperature

� No recovery possible

27 operating points

� SO2 concentration in air

– 0.1 ppm, 1 ppm and 4 ppm

� Constant voltage operation

– 0.85 V, 0.7 V and 0.55 V

� Cell temperature

– 43°C, 70°C and 87°C


H2-crossover and membrane resistance – SO2

� H2-crossover increase at elevated temperature

� Courses of H2-crossover and membrane resistance are identical to the reference measurements

� Same results for all harmful gases


Harmful gas screening SO2

Most important results of SO2 test series

� Strong current loss with SO2 concentration of 1 ppm and 4 ppm in air

� Slightly lower degradation at elevated temperature

� CVs, in which the cell was exposed to high voltages up to 1 V, do not result in significant regeneration

� Comparison of electrochemical catalyst surface between reference measurements without contamination and measurements with SO2 in air

� Stronger reduction of electrochemical catalyst surface area starting at 1 ppm SO2 in air


Harmful gas screening NH3

� NH3 concentration in air



– 0.85 V, 0.7 V and 0.55 V


– 43°C, 70°C and 87°C

� No influence within one hour under contamination with 0.5 ppm and 3 ppm NH3 in air

� Contamination with 8 ppm in air result in strong current drops


� Only slight recovery possible within one hour


Harmful gas screening NH3

Most important results of NH3 test series

� Influence of NH3 on PEFC is temperature dependent

� Power loss is slightly dependent on the potential. In percentage terms the largest power loss occurs at high potential.

� The regeneration of the cell is highly temperature dependent. A rapid current recovery takes place by charging the cathode side with clean air at elevated cell temperatures.

� At 43 °C regeneration cannot be observed within the first hour after cathode contamination

� The ECSA reduction is nearly the same for all temperature levels and harmful gas concentration. A connection between charge decay and voltage profile or regeneration does not seem to exist.


Harmful gas screening Toluene

� C7H8 concentration in air



– 0.85 V, 0.7 V and 0.55 V


– 43°C, 70°C and 87°C

� Negligible influence within one hour under contamination with 0.1 ppm C7H8 in air

� Contamination with 1 ppm in air results in current drop, strong current decline with 3 ppm in air


� Rapid recovery possible within one hour


Harmful gas screening Toluene

Most important results of C7H8 test series

� Influence of C7H8 on PEFC is temperature dependent

� Contamination with 1 ppm in air results in current drop, strong current decline with 3 ppm in air

� Degradation and recovery are temperature dependent

� During supply of the highest concentration of 3 ppm C7H8 in air substantial current losses can be recognized at all temperatures and potentials

� At 43 °C the regeneration after one hour is only partially completed. At 87°C the regeneration occurs within a few minutes.

� The ECSA obtained from the CV measurements in comparison with the basic characteristic does not exhibit increased charge decay at the temperatures of 87°C and 70°C. However, enhanced charge decline is determined at 43°C.


Harmful gas screening Ethane

� C2H6 concentration in air

– 1 ppm, 3 ppm and 8 ppm


– 0.85 V, 0.7 V and 0.55 V


– 43°C, 70°C and 87°C

� The behavior of the current density at constant voltage, voltage profile and the decrease of ECSA corresponds to the results from the basic characteristics without contamination

� Degradation caused by ethane cannot be detected. This is independent of cell temperature, potential and ethane concentration


Harmful gas screening NO

� NO concentration in air



– 0.85 V, 0.7 V and 0.55 V


– 43°C, 70°C and 87°C

� 1 ppm NO in air leads to considerable current losses. The current loss is strongly dependent on the temperature

� High current losses at 10 ppm and 15 ppm NO in air. After some time the current approaches a limit value.


Harmful gas screening NO

Most important results of NO test series

� Even 1 ppm NO in air leads to considerable current losses. A tendency to approach a limit of current decline cannot be seen within one hour of contamination.

� The current loss is strongly dependent on the temperature. However, a slight potential dependence can be observed as well. Maximum current losses are determined at 0.85 V level.

� 10 ppm NO in cathode air supply leads to very strong and rapid current drop within a few minutes. Again, the strength of the current loss is temperature and also potential dependent

� Recovery is temperature dependent


Harmful gas screening NO2

� NO2 concentration in air



– 0.85 V, 0.7 V and 0.55 V


– 43°C, 70°C and 87°C

� No influence of 1 ppm NO in air within one hour.

� High current losses at 10 ppm an 15 ppm NO2 in air. After some time the current approaches a limit value

� Fast but not complete recovery within one hour


Harmful gas screening NO2

Most important results of NO2 test series

� At the temperature levels of 87°C and 70°C and a contamination of 1 ppm NO2 only a slight negligible power loss can be identified. At a temperature of 43°C current decreases to 3.5 % within one hour of contamination.

� At all operating points with a concentration of 10 ppm NO2 in supplied air the current drops directly after the start of injection. After about 30 minutes the current drops more slowly and approaches a static value.

� The current loss is dependent on the temperature. The lower the temperature the stronger the current declines.

� The current loss is also affected by the cell potential, the higher the cathode potential the stronger the current loss.

� Depending on the temperature the cell current can be almost completely regenerated within one hour.

� Regardless of the cell potential no complete regeneration is possible at a temperature of 43°C over a long period.


Harmful gas screening Comparison between NO and NO2

� Contrary to NO2 even 1 ppm NO in air leads to a considerable current loss

� At 10 ppm NO/NO2

current losses are almost identical


Harmful gas screening Comparison between NO and NO2 - Influence of temperature

� Recovery is strongly temperature dependent

� A complete regeneration is not possible at a temperature level of 43°C


Content




– SO2, NH3, C7H8 ,C2H6, NO, NO2


– NH3, NO and NO2








b) with clean air

� Summary


Influence of humidity1 ppm NH3 in air – 100% vs. 40% humidity at cathode side

� First strong current drop, followed by a slower linear current loss

� Current loss of 20 A while harmful gas addition - regardless of the humidification

� Slightly faster regeneration at 100% humidity

� Complete recovery could not be achieved

100 % humidification 40 % humidification


Influence of humidity1 ppm NO in air vs. 1 ppm NO2 in air

� No higher voltage losses by reducing humidity

� Strong voltage loss during contamination with NO

� Once again, a significantly stronger degradation of NO compared to NO2 can be seen

1 ppm NO in air 1 ppm NO2 in air


Content




– SO2, NH3, C7H8 ,C2H6, NO, NO2


– NH3, NO and NO2








b) with clean air

� Summary


Long term test with SO2

200 h

� Linear voltage loss during test period, but unexpectedly strong voltage drops with subsequent regeneration take place.

� Suspected accumulation of SO2 on active catalyst surfaces

But what is the explanation for the strong voltage drops with subsequent regeneration???

� Current loss: 27 mA h-1



Influence of NO during measurements with SO2

� High impact of NOx, especially NO, during long term test with SO2

� Maximum NO peak during measurement: 250 ppb

� Consequence for further measurements � Integration of air filter

At standard conditions:1 ppb NO ~ 1,2471 µg/m³1 ppb NO2 ~ 1,9123 µg/m³



Influence of NO during measurements with SO2 – EIS measurements

� Impedance measurements are consistent with the current losses

� Changes in charge transfer resistance



Accumulation of SO2 and reversible degradation

� Linear correlation between concentration and loss of current is not clearly established

� Current loss of 27 mA h-1 - but reversible degradation

� Comparison of voltage before SO2 supply and after SO2 supply + 7 days downtime indicates that no irreversible degradation took place during contamination with 10 ppb SO2


Content




– SO2, NH3, C7H8 ,C2H6, NO, NO2


– NH3, NO and NO2








b) with clean air

� Summary


Realistic NOx concentrations and limit values„Unintended“ influence of NOx

Typical NOx trends during daily commuting traffic

� NO data measured ~10 km away of ZBT laboratory

� Peak base concentration: 200 ppb

� Measurement ~ 500 m beside highway

� Maximum voltage loss: 3%


Realistic NOx concentrations and limit valuesFilter increases lifetime of stack in long term perspective

Outdoor measurement 2011

� 2 stacks / 5 cells / 50 cm2 in recirculated H2 powered fuel cell system

– stack A: Without cathode filter

– stack B: With cathode filter (particles, NOx)

� After three weeks testing significant difference between filtered and unfiltered system:

– voltage level significantly reduced

– stronger reaction on NO level

Untersuchungen zum Einfluss von Schadgasen auf der Kathodenseite von PEM-BZ - vertraulich -

At standard conditions:1 ppb NO ~ 1,2471 µg/m³1 ppb NO2 ~ 1,9123 µg/m³


Content




– SO2, NH3, C7H8 ,C2H6, NO, NO2


– NH3, NO and NO2








b) with clean air

� Summary


Realistic NOx concentrations and limit valuesLimit values

NO2NO

� Influence of NO on cell voltage already at concentration level of 100 ppb

� Recognizable voltage drop by NO2 at concentration level of 250 ppb

� Response on NO is stronger than on NO2

� Higher voltages after test run

– indication for side effects

– potentially harmful in long term perspective


Realistic NOx concentrations and limit valuesEIS analysis of 1ppm NO tests

� Further tests are currently being carried out

� Evaluations of additional impedance measurements follow soon - including modeling with fitting


� EIS Analysis of 1ppm NO tests:

– strong immediate impact on catalyst (first hour)

– at longer exposition: no further catalyst incidents, but diffusion resistances decrease slightly


Realistic NOx concentrations and limit valuesPossibility of regeneration - contaminated air vs. clean air

� Stronger and faster voltage decline with NO

� Recovery under contaminated air faster and more completed during experiments with NO2

� Full recovery possible only with uncontaminated air


Realistic NOx concentrations and limit valuesInfluence of NO vs. NO2

� Stronger and faster voltage decline with NO

� NO: After about 60 minutes the current drops more slowly and approaches a static value

� NO2: After about 180 minutes the current drops more slowly and approaches a static value


Realistic NOx concentrations and limit valuesPossibility of regeneration

� Current decline starting at 500 ppb NO in air

� Full recovery possible only with uncontaminated air

� Constant voltage operation at 0.7 V

� Cell temperature 80°C


Realistic NOx concentrations and limit valuesPossibility of regeneration – temperature dependent

� Full regeneration only at very low concentration

� Regeneration is highly dependent on temperature

� Higher temperature ensures faster regeneration



Realistic NOx concentrations and limit valuesPossibility of regeneration – potential dependent

� Contamination with NO at different potentials reveal a potential dependent during recovery

� The lower the potential the faster regeneration

� No complete regeneration is possible at cell potential of 0.8 V


Content




– SO2, NH3, C7H8 ,C2H6, NO, NO2,


– NH3, NO and NO2








b) with clean air

� Summary


Summary

� The harmful gas screening revealed a negative influence of all components (SO2, NH3, C7H8, NO, NO2) except for ethane (C2H6)

� Only SO2 showed a completely irreversible impact that was accounted to the irrecoverable adsorption on the catalyst

� A dependence of the temperature was found for all investigated pollutants. A lower temperature always led to a stronger negative influence of the pollutants.

� Recovery is temperature dependent

� Influence of humidity could not be observed (NH3, NO and NO2)


– linear voltage loss during test period, but unexpectedly strong voltage drops with subsequent regeneration caused by NOx took place

– comparison of voltage before SO2 supply and after SO2 supply + 7 days downtime indicates that no irreversible degradation took place during contamination with 10 ppb SO2


Summary

Particular studies with NOx

� The results revealed a clear difference of the influence of NO and NO2 at low concentration (≤1 ppm)

� Influence of NO on cell voltage already at concentration level of 100 ppb

� Recognizable voltage drop by NO2 at concentration level of 250 ppb

� Stronger and faster voltage decline with NO compared to NO2

� Recovery under contaminated air faster and more completed during experiments with NO2

compared to NO

� Full recovery possible only with uncontaminated air!!!

� Contamination with NO at different potentials reveal a potential dependent during recovery

– the lower the potential the faster regeneration

– no complete regeneration is possible at cell potential of 0.8 V

� Higher voltages after test run

– indication for side effects

– potentially harmful in long term perspective

Thank you for your attention!

Contact:

www.zbt-duisburg.de

Zentrum für BrennstoffzellenTechnik GmbH

Ulrich Misz

+49-203-7598-3313

[email protected]

This project is being supported byGerman ministry of economicsBMWi under grant number03ET6036A

(01.12.2014 - 31.05.2017)

Documents

Impact of air pollutants on PEM fuel cells · Conditioning Contamination Recovery EIS Cleaning CV CV CV RAP 1 hour without contaminant 1 hour with contaminant 1 hour without contaminant