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Research Paper

A Model of a High-Temperature Direct Methanol Fuel Cell

[+] Author and Article Information
K. Scott

e-mail: k. scott@newcastle.ac.uk

M. Mamlouk

School of Chemical Engineering
and Advanced Materials,
University of Newcastle Upon Tyne,
Merz Court,
Newcastle-Upon-Tyne NE1 7RU, UK

Contributed by the Advanced Energy Systems Division of ASME for publication in the Journal of Fuel Cell Science and Technology. Manuscript received March 7, 2011; final manuscript received October 5, 2012; published online August 20, 2013. Assoc. Editor: Jacob Brouwer.

J. Fuel Cell Sci. Technol 10(5), 051003 (Aug 20, 2013) (12 pages) Paper No: FC-11-1037; doi: 10.1115/1.4024833 History: Received March 07, 2011; Revised October 05, 2012

A steady-state, isothermal, one-dimensional model of a direct methanol proton exchange membrane fuel cell (PEMFC), with a polybenzimidazole (PBI) membrane, was developed. The electrode kinetics were represented by the Butler–Volmer equation, mass transport was described by the multicomponent Stefan–Maxwell equations and Darcy's law, and the ionic and electronic resistances described by Ohm's law. The model incorporated the effects of temperature and pressure on the open circuit potential, the exchange current density, and diffusion coefficients, together with the effect of water transport across the membrane on the conductivity of the PBI membrane. The influence of methanol crossover on the cathode polarization is included in the model. The polarization curves predicted by the model were validated against experimental data for a direct methanol fuel cell (DMFC) operating in the temperature range of 125–175 °C. There was good agreement between experimental and model data for the effect of temperature and oxygen/air pressure on cell performance. The fuel cell performance was relatively poor, at only 16 mW cm−2 peak power density using low concentrations of methanol in the vapor phase.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Schematic diagrams of the anode and cathode 1D model cross section regions. Anode: AF—flow channel, AD—diffusion layer, AM—microporous layer, AR—catalyst layer. Membrane: M—membrane. Cathode: CF—flow channel, CD—diffusion layer, CM—microporous layer, CR—catalyst layer.

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Fig. 2

Thin film model in a DMFC

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Fig. 3

Anode current density versus potential. Temperature 150 °C and 1 M methanol vapor.

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Fig. 4

Cathode current versus potential for conditions for air and oxygen. γ=0.5. □—air, temperature 150 °C, •—oxygen, temperature 150 °C.

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Fig. 5

(a) Comparison between model and experiment for anode polarization, at different temperatures. 1 g m−2, 60% PtRu/C 20% Ru, width 12 μm, pressure 1 bar (atmospheric pressure), and 1 M methanol feed. Continuous line, experimental 125 °C ; line with single dashes, experimental 150 °C ; line with double dashes, experimental 175 °C ; model 125 °C—; model 150 °C—♦; model 175 °C—○. (b) Comparison between model and experiment for anode polarization, at different temperatures. Plotted for loading 1 mg cm−2, 60% PtRu/C 20% Ru, width 12 μm, pressure 1 bar (atmospheric pressure), and 2 M methanol feed. Continuous line, experimental 125 °C ; line with single dashes, experimental 150 °C ; line with double dashes, experimental 175 °C ; model 125 °C—; model 150 °C—♦; model 175 °C—○.

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Fig. 6

(a) Comparison between model and experiment for cathode polarization, at different temperatures. Loading 0.5 mg cm−2, 60% PtRu/C 20% Ru, width 12 μm, pressure 1 bar (atmospheric pressure), air feed. Continuous line, experimental 125 °C ; line with single dashes, experimental 150 °C ; line with double dashes, experimental 175 °C ; model 125 °C—; model 150 °C—♦; model 175 °C—○. (b) Comparison between model and experiment for cathode polarization, at different temperatures. Loading 0.5 mg cm−2, 60% PtRu/C 20% Ru, width 12 μm, pressure 1 bar (atmospheric pressure), oxygen feed. Continuous line, experimental 125 °C ; line with single dashes, experimental 150 °C ; line with double dashes, experimental 175 °C ; model 125 °C—; model 150 °C—♦; model 175 °C—○.

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Fig. 7

Comparison between model and experiment fuel cell polarization at different temperatures. Air cathode and 1 M methanol. Continuous line, experimental 125 °C ; line with single dashes, experimental 150 °C ; line with double dashes, experimental 175 °C ; continuous thick line, experimental power 125 °C ; thick line, with single dashes, experimental power density 150 °C ; thick line with double dashes, experimental power 175 °C ; model 125 °C—; model 150 °C—♦; model 175 °C—○; model power cell 125 °C—○; model power cell 150 °C—□; model power cell 175 °C—▴

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Fig. 8

Comparison between model and experiment for fuel cell polarization. Oxygen cathode and 1 M methanol. Continuous line, experimental 125 °C, ; line with single dashes, experimental 150 °C, ; line with double dashes, experimental 175 °C, ; continous thick line, experimental power 125 °C, ; thick line with single dashes, experimental power density 150 °C, ; thick line with double dashes, experimental power 175 °C, ; model 125 °C—; model 150 °C—♦; model 175 °C—○; model power cell 125 °C—○; model power cell 150 °C—□; model power cell 175 °C—▴

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Fig. 9

(a) Modulus of electronic current density in the anode catalyst layer. •—150 mV, ○—310 mV, ▴—450 mV. (b) Modulus of ionic current density in the anode catalyst layer. •—150 mV, □—310 mV, ▴—450 mV.

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Fig. 10

(a) Methanol concentration at the thin film/PtRu surface (the site of the reaction) in the anode. Potentials: ▴—150 mV, •—450 mV. (b) Methanol concentration at the thin film/PtRu surface (the site of the reaction) at the anode. The thin film thickness was increased by an order of magnitude. ▴—150 mV, •—450 mV.

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Fig. 11

Oxygen concentration on the thin film/Pt surface (the site of the reaction), cathode, model results. ▴—400 mV, •—100 mV. The cathode catalyst x coordinates range from 20 μm (membrane) to 35 μm.

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