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Your search keyword '"Cleemann, L. N."' showing total 11 results
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11 results on '"Cleemann, L. N."'

1. Fuel Cell Electrolytes of Polybenzimidazole Membranes Cross-linked with Bis(chloromethyl) Arenes

Author

Kirkebæk, A., Aili, D., Yue, B., Vassiliev, A., Cleemann, L. N., Jensen, J. O., Li, Q., Kirkebæk, A., Aili, D., Yue, B., Vassiliev, A., Cleemann, L. N., Jensen, J. O., and Li, Q.

Abstract

Cross‐linking of phosphoric acid doped polybenzimidazole membranes as fuel cell electrolytes represents an attractive approach to improving the mechanical robustness at a high acid loading. Numerous cross‐linking concepts have been reported in the literature, but a deeper understanding of how the cross‐linking chemistry affects the physicochemical properties of the membrane and its fuel cell performance and durability remains to be assessed. In this work, a series of cross‐linked membranes are prepared using cross‐linking agents of different regio‐chemistry and steric nature. It is shown, that the nature of the cross‐linking agent has a large impact on the effective degree of cross‐linking, which in turn determines the acid doping characteristics and ultimately the fuel cell performance and acid retention during long‐term operation.

Published
2018

2. Acid Distribution and Durability of HT-PEM Fuel Cells with Different Electrode Supports

Author

Kannan, A., Li, Q., Cleemann, L. N., Jensen, J. O., Kannan, A., Li, Q., Cleemann, L. N., and Jensen, J. O.

Abstract

The durability of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) was studied with phosphoric acid doped membranes of polybenzimidazole (PBI). One of the challenges for this technology is the loss and instability of phosphoric acid resulting in performance degradation after long-term operation. The effect of the gas diffusion layers (GDL) on acid loss was studied. Four different commercially available GDLs were subjected to passive ex situ acid uptake by capillary forces and the acid distribution mapped over the cross-section. Materials with an apparent fine structure made from carbon black took up much more acid than materials with a more coarse apparent structure made from graphitized carbon. The same trend was evident from thermally accelerated fuel cell tests at 180 °C under constant load where degradation rates depended strongly on the choice of GDL material, especially on the cathode side. Acid was collected from the fuel cell exhaust at rates clearly correlated to the fuel cell degradation rates, but amounted to less than 6% of the total acid content in the cell even after significant degradation. Long-term durability of more than 5,500 h with a degradation rate of 12 µV h−1 at 180 °C and 200 mA cm−2 was demonstrated with the GDL that retained acid most efficiently.

Published
2018

5. Preparation, study and modification of nanometer scale flat TiO2 surfaces by electrochemistry and AFM techniques

Author

Dinh Thi, Mai Thanh, Cleemann, L. N., Welander, A. C., Devilliers, Didier, Mahé, Eric, Balnois, Eric, Liquides Ioniques et Interfaces Chargées (LI2C), Université Pierre et Marie Curie - Paris 6 (UPMC)-Ecole Superieure de Physique et de Chimie Industrielles de la Ville de Paris (ESPCI Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), and Mahe, Eric

Subjects
[PHYS.PHYS.PHYS-CHEM-PH]Physics [physics]/Physics [physics]/Chemical Physics [physics.chem-ph], ComputingMilieux_MISCELLANEOUS, [PHYS.PHYS.PHYS-CHEM-PH] Physics [physics]/Physics [physics]/Chemical Physics [physics.chem-ph]
Abstract

International audience

Published
2003

9. High Molecular Weight Polybenzimidazole Membranes for High Temperature PEMFC.

Author

Yang, J. S., Cleemann, L. N., Steenberg, T., Terkelsen, C., Li, Q. F., Jensen, J. O., Hjuler, H. A., Bjerrum, N. J., and He, R. H.

Subjects
MOLECULAR weights, PROTON exchange membrane fuel cells, PHOSPHORIC acid, PERFORMANCE of fuel cells, PROTON conductivity
Abstract

High temperature operation of proton exchange membrane fuel cells under ambient pressure has been achieved by using phosphoric acid doped polybenzimidazole (PBI) membranes. To optimize the membrane and fuel cells, high performance polymers were synthesized of molecular weights from 30 to 94 kDa with good solubility in organic solvents. Membranes fabricated from the polymers were systematically characterized in terms of oxidative stability, acid doping and swelling, conductivity, mechanical strength and fuel cell performance and durability. With increased molecular weights the polymer membranes showed enhanced chemical stability towards radical attacks under the Fenton test, reduced volume swelling upon the acid doping and improved mechanical strength at acid doping levels of as high as about 11 mol H3PO4 per molar repeat polymer unit. The PBI-78kDa/10.8PA membrane, for example, exhibited tensile strength of 30.3 MPa at room temperature or 7.3 MPa at 130 °C and a proton conductivity of 0.14 S cm-1 at 160 °C. Fuel cell tests with H2 and air at 160 °C showed high open circuit voltage, power density and a low degradation rate of 1.5 μV h-1 at a constant load of 300 mA cm-2. [ABSTRACT FROM AUTHOR]

Published
2014
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10. Catalytic Reduction of NO by Methane Using a Pt/C /polybenzimidazole/Pt/C Fuel Cell.

Author

Petrushina, I. M., Cleemann, L. N., Refshauge, R., Bjerrum, N. J., and Bandur, V. A.

Subjects
METHANE, FUEL cells, ELECTROCHEMISTRY, DIRECT energy conversion, POLARIZATION (Electricity), ADSORPTION (Chemistry), CATALYSTS, HYDROGEN as fuel, SURFACE chemistry
Abstract

The catalytic NO reduction by methane was studied using a (NO,CH4,Ar),Pt∣polybenzimidazole(PBI)-H3PO4∣Pt,(H2,Ar) fuel cell at 135 and 165°C. It has been found that, without any reducing agent (like CH4), NO can be electrochemically reduced in the (NO, Ar), Pt/C∣PBI-H3PO4∣Pt/C, (H2,Ar) fuel cell with participation of H+ or electrochemically produced hydrogen. When added, methane partially suppresses the electrochemical reduction of NO. Methane outlet concentration monitoring has shown the CH4 participation in the chemical catalytic reduction, i.e., methane co-adsorption with NO inhibited the electrochemical NO reduction and introduced a dominant chemical path of the NO reduction. The products of the NO reduction with methane were N2, C2H4, and water. The catalytic NO reduction by methane was promoted when the catalyst was negatively polarized (-0.2 V). Repeated negative polarization of the catalyst increased the NO conversion. Maximum NO conversion was 48%. This effect was explained as a result of the reaction of the electrochemically produced hydrogen. [ABSTRACT FROM AUTHOR]

Published
2007
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11. Catalytic Reduction of NO by Methane Using a Pt ∕ C ∕ polybenzimidazole ∕ Pt ∕ C Fuel Cell

Author

Petrushina, I. M., Cleemann, L. N., Refshauge, R., Bjerrum, N. J., and Bandur, V. A.

Abstract

The catalytic NO reduction by methane was studied using a (NO,CH4,Ar),Pt∣polybenzimidazole(PBI)–H3PO4∣Pt,(H2,Ar)fuel cell at 135 and 165°C. It has been found that, without any reducing agent (like CH4), NO can be electrochemically reduced in the (NO, Ar), Pt∕C∣PBI–H3PO4∣Pt∕C, (H2,Ar)fuel cell with participation of H+or electrochemically produced hydrogen. When added, methane partially suppresses the electrochemical reduction of NO. Methane outlet concentration monitoring has shown the CH4participation in the chemical catalytic reduction, i.e., methane co-adsorption with NO inhibited the electrochemical NO reduction and introduced a dominant chemical path of the NO reduction. The products of the NO reduction with methane were N2, C2H4, and water. The catalytic NO reduction by methane was promoted when the catalyst was negatively polarized (−0.2V). Repeated negative polarization of the catalyst increased the NO conversion. Maximum NO conversion was 48%. This effect was explained as a result of the reaction of the electrochemically produced hydrogen.

Published
2007
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