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Research Papers

The Influence of Chitosan Membrane Properties for Direct Methanol Fuel Cell Applications

[+] Author and Article Information
Peter O. Osifo

 Department of Chemical Engineering, Vaal University of Technology, P/Bag X021, Vanderbijlpark 1900, South Africapetero@vut.ac.za

Aluwani Masala

 Department of Chemical Engineering, Vaal University of Technology, P/Bag X021, Vanderbijlpark 1900, South Africa

J. Fuel Cell Sci. Technol 9(1), 011003 (Dec 19, 2011) (9 pages) doi:10.1115/1.4005382 History: Received March 15, 2010; Revised September 23, 2011; Published December 19, 2011; Online December 19, 2011

The chitosan membranes with different degrees of deacetylation (dda), prepared from Cape rock lobster collected from the surroundings of Cape Town, South Africa were characterized for suitability in methanol fuel cell applications. A comparison of chitosan membranes characteristics and that of conventional Nafion 117 membranes were made. Following this, the chitosan membranes were chemically modified with sulfuric acid to improve its proton conductivity and mechanical properties. A mass balance on proton transfer across the membrane resulted in a second order differential equation. Experimental data fitted into the equation gives a linear curve that was used to determine the membrane resistance. It was found that the dda of the chitosan membranes affected the water uptake, thereby affecting the proton flow. At a temperature of 20°C, chitosan membranes with a difference of 10% dda have a difference of about 5% water content. Chitosan membranes with a lower dda were found to have higher water content resulting in lower membrane resistances to proton flow. The water content of chitosan membranes was higher than Nafion membranes. The average resistance to proton flow for chitosan membrane was 53 min/cm and a Nafion membrane was 78 min/cm. Thermogravimetry analysis shows that chitosan membrane with higher dda is more thermally stable than chitosan with lower dda, Nafion membranes were more stable at higher temperature than chitosan membranes, Nafion membranes could decompose at temperature of 320 °C while chitosan membranes at 230 °C. Methanol permeability through chitosan membrane of higher dda was more than with one lower dda, however, the permeability through chitosan was three times lower when compares to Nafion membranes under the same temperature and pressure conditions. The performance of chitosan membranes and Nafion 117 membranes measured from a single cell DMFC with Pt-Ru/C anode catalysts and Pt/C cathode catalysts showed that Nafion membranes have a better performance. This was because the current and peak power densities determined for Nafion membranes were 0.56 A/cm2 and 0.075 W/cm2 , respectively, and for Chit-I, were 0.22 A/cm2 and 0.0274 W/cm2 , respectively, and for Chit-II membrane, were 0.26 A/cm2 and 0.0424 W/cm2 , respectively.

Copyright © 2012 by American Society of Mechanical Engineers
Topics: Membranes , Water , Methanol
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Figures

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Figure 1

Chitosan preparation from chitin

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Figure 2

Chitosan cross linked with sulfuric acid

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Figure 3

Schematic diagram of a diffusion cell

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Figure 4

SEM images of cross section of chitosan membrane and catalyzed chitosan membrane

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Figure 5

Schematic diagram of an air-breathing DMFC

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Figure 6

IR spectra of Chit-I and Chit-II showing the proposed baseline (B) for determining the absorbance ratio A1655 /A3450

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Figure 7

IR spectra of (1) Chit-II flakes, (2) Chit-II membrane, (3) Chit-I flakes, and (4) Chit-I membrane

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Figure 8

% water uptake of membranes as a function drying and rehydration temperature

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Figure 9

TG thermograms for Nafion 117, Chit-I, and Chit-II membranes under nitrogen

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Figure 10

TG, DTG, and DSC thermograms for Chit-I membranes under nitrogen

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Figure 11

TG, DTG, and DSC thermograms for Chit-II membranes under nitrogen

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Figure 12

Methanol permeability through Chitosan and Nafion membranes

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Figure 13

The change in hydronium ion concentration with time through Chit-I membranes

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Figure 14

The change in hydronium ion concentration with time though Chit-II membranes

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Figure 15

Determination of the membrane resistance for Chit-I, Chit-II, and Nafion 117 membranes

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Figure 16

Plot of cell voltage against current density for a DMFC fed by 1M methanol under atmospheric temperature with Chit-II MEA, Chit-II MEA, and Nafion 117 MEA

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