Iron Cation Contamination Effect on the Performance and Lifetime of the MEA Dr Ahmad El-kharouf Centre for Hydrogen and Fuel Cells Research www.fuelcells.bham.ac.uk Hydrogen Days 2016, Prague
Content Motivation - STAMPEM Literature overview Methodology Results and discussion Conclusions Slide 2 / 26
Motivation The use of metallic BPPs in PEFC stacks: Are their any contaminants leaching from the BPP? How much of it is absorbed into the MEA? How is it affecting the MEA? Slide 3 / 26
Motivation Contaminants level was measured using Inductive couples plasma (ICP) method for MEAs after operation Results showed an increase in Fe and Cr concentration even for coated samples. What is the effect of the contaminants on the performance and lifetime of the MEA? Slide 4 / 26
STAMPEM Ex-situ introduction of contaminants to MEAs MEA Fe Concentration (µl/g) JM fresh MEA 14 JM MEA (, 10 PPM Fe) 77 GoreTek Fresh MEA 4.5 GoreTek MEA (, 10 PPM Fe) 160 10PPM Fe + 24 hrs Slide 5 / 26
Cell voltage (V) STAMPEM 1.0 JM_Fresh MEA JM MEA 10PPM Fe GoreTek_Fresh MEA GoreTek MEA 10PPM Fe 0.8 0.6 0.4 0.2 0.0 0.5 1.0 1.5 Current density (A.cm -2 ) Slide 6 / 26
STAMPEM MEA OCV (air) (V) I @ 0.6V (air) (A.cm -2 ) Cell ohmic resistance (mω.cm2) @ 0.8V JM fresh MEA 0.95 0.79 160 JM MEA (, 10 PPM Fe) 0.90 0.43 195 GoreTek Fresh MEA 0.95 0.77 150 GoreTek MEA (, 10 PPM Fe) 0.86 0.22 370 Slide 7 / 26
STAMPEM MEA failure after short operation 8 hrs at 0.6 V Polarisation curve and EIS characterisation Degradation of the MEA on the around the edges of BPP and Gasket layer Operation < 10 hrs Slide 8 / 26
Literature overview Elements leaching from fuel cell system components. These elements are deposited in either the catalyst layer or the polymer membrane. Fe Al Pt Cu Ni Si air Pipes BPP Humidifier H 2 MEA Slide 9 / 26
Literature overview Effect of contaminants: Reduction in the performance Decrease in membrane conductivity Affect water diffusion through the membrane Fe Slide 10 / 26
Overview overview Effect of contaminants: Reduction in the performance Enhance the membrane degradation rate Increase radicals formation Membrane decomposition - Lower EW - Lower conductivity S. Zhang et al, Int. J. Hydrogen Energy. 34 (2009) Z. Luo et al, Int. J. Hydrogen Energy. 31 (2006) T. Kinumoto et al, J. Power Sources. 158 (2006) Slide 11 / 26
Methodology Introduction of contaminants Effect of Fe 2+ concentration ( ) Iron concentration Effect of H 2 concentration (10 PPM Fe 2+ ) Hydrogen peroxide concentration 0 PPM 0% 5 PPM 5% 10 PPM 10% 20 PMM 36 cm 2 Nafion 212 250ml solution at 70 C with constant stirring Slide 12 / 26
Methodology X-ray Fluorescence Ex-situ assessment Contamination level Proton Conductivity Ion Exchange Capacity 4- wire Kelvin at 70 o C & 80% RH Acid-Base titration method Slide 13 / 26
Methodology In-situ assessment MEAs were fabricated and tested in-situ Polarisation curves (IV) Electrochemical Impedance Spectroscopy (EIS) Cyclic voltammetry (CV) Operating conditions T : 70 C P : 2 bar RH:100% anode, 50% cathode Stoichiometry:1.2 anode, 2.4 cathode Slide 14 / 26
Results and Discussion The solution colour cleared after 24hrs. After 4hrs No measurable change in ph is detected. Visual inspection showed no defects in the membrane. Fe 20PPM, Slide 15 / 26
Fe Wt% (%) Results and Discussion The effect of Fe concentration 0.20 0.15 0.10 0.05 XRF results: Change in Fe loading with the change in Fe concentration 0.00 0ppm Fe, 5ppm Fe, 10ppm Fe, 20ppm Fe, Slide 16 / 26
Proton conductivity (S.cm -1 ) Results and Discussion The effect of Fe concentration 0.07 0.06 0.05 0.04 Change in proton conductivity with the change in Fe concentration 0.03 0.02 fresh 0ppm Fe, 5ppm Fe, 10ppm Fe, 20ppm Fe, Slide 17 / 26
IEC (mequiv/g) Results and Discussion The effect of Fe concentration 2.0 1.5 1.0 0.5 Change in Ion Exchange capacity with the change in Fe concentration 0.0 fresh 0ppm Fe, 5ppm Fe, 10ppm Fe, 20ppm Fe, Slide 18 / 26
Cell voltage (V) Results and Discussion The effect of Fe concentration No change in OCP, Ohmic resistance or CV for the MEA. 1.0 Fresh _0PPm Fe_10%H2O2 _10PPm Fe_10% H2O2 _20PPm Fe_10% H2O2 The increase in iron level increases performance drop. 0.8 0.6 0.4 0.0 0.5 1.0 1.5 Current density (A.cm -2 ) Slide 19 / 26
Fe Wt% (%) Results and Discussion The effect of H 2 concentration 1.0 0.8 0.6 0.4 XRF results: Change in Fe loading with the change in H 2 concentration 0.2 0.0 10ppm Fe, 0% H 2 10ppm Fe, 5% H 2 10ppm Fe, 10% H 2 Slide 20 / 26
Proton conductivity (S.cm -1 ) Results and Discussion The effect of H 2 concentration 0.07 0.06 0.05 Change in proton conductivity with the change in H 2 concentration 0.04 0.03 0.02 fresh 10ppm Fe, 0% H 2 10ppm Fe, 5% H 2 10ppm Fe, Slide 21 / 26
IEC (mequiv/g) Results and Discussion The effect of H 2 concentration 2.0 1.6 1.2 0.8 Change in Ion Exchange capacity with the change in H 2 concentration 0.4 0.0 fresh 10ppm Fe, 0% H 2 10ppm Fe, 5% H 2 10ppm Fe, Slide 22 / 26
Cell voltage (V) Results and Discussion The effect of H 2 concentration No change in OCP, Ohmic resistance or CV for the MEA. 1.0 Fresh _10PPm Fe_H2O _10PPm Fe_5% H2O2 _10PPm Fe_10% H2O2 No clear negative effect of H 2 0.8 0.6 0.4 0.0 0.5 1.0 1.5 Current density (A.cm -2 ) Slide 23 / 26
Conclusions The presence of the catalyst layer significantly increases the effect of the contaminants. Low levels of Fe result in a significant change in the membrane properties. H 2 concentration in the presence of Fe has relatively small effect on the MEA performance. Proton conductivity is the primary property affected by the iron contamination, however; the effect on the membrane structure is still need to be explored. Slide 24 / 26
Future work A systematic study of the effect of cations in the presence of Pt catalyst layer. Quantification of leaching rate of cations from metallic BPPs degradation a characterisation property for metallic plates. The effect of other elements on the performance of the MEA. Slide 25 / 26
Acknowledgement Prof Robert Steinberger-Wilckens Carolina Branco Dr Surbhi Sharma Centre for Hydrogen and Fuel Cell research University of Birmingham Thank you for listening Slide 26 / 26