Catalysis for Direct Methanol Fuel Cells

Chapter

Abstract

The direct methanol fuel cell (DMFC) is a particular case of a low-temperature proton exchange membrane (PEM) fuel cell (FC). A DMFC utilizes CH3OH as anode fuel and O2 as cathode fuel. Depending on the application, a DMFC is typically operated in the range of 40–80°C. DMFCs are very attractive due to the high energy density of CH3OH, thus making them lightweight devices. In fact, DMFCs can have 15 times the energy density of a Li-ion battery. Other advantages are that DMFCs can be refueled on the fly within seconds, and CH3OH is an inexpensive and readily available fuel. Furthermore, CH3OH is a liquid, thus facilitating its distribution, and it can be taken on airplanes in designated cartridges. The impact of the eventual successful commercialization of DMFCs is estimated to be large and expands into the microelectronics industry. However, significant obstacles need to be overcome before DMFCs can be truly considered to be a viable technology. Some of these challenges are related to the anode catalyst such as lowering the cost of the catalyst used by lowering the amount of the noble metal component, as well as extending the lifetime of both the anode and cathode catalysts. A number of reviews describing the technical aspects of DMFCs as an entire device are available (Scott et al. J Power Sources 79:43–59, 1999; Lamm and Müller System design for transport applications. In: Vielstich et al. (ed) Handbook of fuel cells fundamentals technology and applications, Wiley, New York, 2003; Narayanan et al. DMFC system design for portable applications. In: Vielstich et al. (ed) Handbook of fuel cells fundamentals technology and applications, Wiley, New York, 2003; Gottesfeld Design concepts and durability challenges for mini fuel cells. In: Vielstich et al. (ed) Handbook of fuel cells fundamentals technology and applications, Wiley, New York, 2009). Therefore, these aspects are not covered in this chapter, which instead focuses on the catalysis aspects of the electrochemical CH3OH oxidation reaction. However, cross-references to proton electrolyte fuel cells (PEMFCs) and related reactions are given where appropriate.

Keywords

Permeability Entropy Porosity Hydrate Enthalpy 

Notes

Acknowledgments

The authors wish to thank the editors who have provided them with the opportunity to write this chapter.

Glossary

A

Surface area [cm2]

AC

Alternating current

α

Symmetry factor

Cdl

Double layer capacitance [F]

CPE

Constant phase element

CV

Cyclic voltammogram

DCOads

Surface diffusion coefficient of –COads [cm2 s−1]

DMFC

Direct methanol fuel cell

Eo

Standard potential [V]

Ea

Activation energy [kJ mole−1]

Eanode

Anode potential [V]

Ecathode

Cathode potential [V]

Ecell

Cell potential [V]

Eeq

Equilibrium potential [V]

EQC

Equivalent circuit

FC

Fuel cell

F

Faraday’s constant [A s mol e− −1 ]

ΔG

Gibb’s free energy [J mol−1]

ΔGo

Gibb’s free energy at standard conditions [J mol−1]

Hads/des

H adsorption and desorption

I

Current [A]

Ilim

Limiting current [A]

IR

IR [Current–resistance, i.e., voltage] drop or Infrared spectroscopy

J

Current density [A cm−2]

Jlim

Limiting current density [A cm−2]

Jo

Exchange current density [A cm−2]

Jo,mass

Exchange current density per catalyst mass limiting current density [A mg Pt −1 ]

K

Equilibrium constant

L

Inductance [H]

MEA

Membrane electrode assembly

ηact

Activation overpotential [V]

ηan

Anode activation overpotential [V]

ηcat

Cathode activation overpotential [V]

ηlim

Potential losses introduced by mass transport limitations [V]

ORR

O2 reduction reaction

P

Power [W]

P*

Power density [W cm−2]

Pmax

Maximal power density [W cm−2]

PEM

Proton exchange membrane

PEMFC

Proton electrolyte fuel cell

p

Partial Pressure

pKa

Negative logarithms of the acid–base constant

R

Gas constant [kJ mol−1 K−1] or Resistance [ohm]

rds

Rate-determining step

QHads/des

Charge for the H ads/des reaction [C]

Qo

Charge passed between t i and t o in a –COads stripping transient [C]

% Qo

Indication of the number of –COads and –OHads sites in close vicinity [%]

% Qo/to

Measurement of the quality of a particular catalyst [% s−1]

T

Temperature [°C or K]

ti

Initiation time for –COads and –OHads recombination reaction [s]

to

Time needed to reach maximal current in –COads stripping transient [s]

Rct

Charge transfer resistance [R]

RHE

Reversible hydrogen electrode

Rm

Resistance of membrane [R]

Rme

Resistance related to poisoning of the catalyst surface [R]

SHE

Standard hydrogen electrode

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Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  1. 1.Institute for Chemical Processes and Environmental TechnologiesNational Research Council of CanadaOttawaCanada
  2. 2.Department of Chemical and Materials EngineeringChang Gung UniversityTaoyuanTaiwan

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