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PEM Fuel Cell


Parts of a Fuel Cell
 Anode
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



Negative post of the fuel cell.
Conducts the electrons that are freed from the hydrogen molecules so that they
can be used in an external circuit.
Etched channels disperse hydrogen gas over the surface of catalyst.

 Cathode





Positive post of the fuel cell
Etched channels distribute oxygen to the surface of the catalyst.
Conducts electrons back from the external circuit to the catalyst
Recombine with the hydrogen ions and oxygen to form water.

 Electrolyte




Proton exchange membrane.
Specially treated material, only conducts positively charged ions.
Membrane blocks electrons.

 Catalyst





Special material that facilitates reaction of oxygen and hydrogen
Usually platinum powder very thinly coated onto carbon paper or cloth.
Rough & porous maximizes surface area exposed to hydrogen or oxygen
The platinum-coated side of the catalyst faces the PEM.


Proton-Exchange Membrane Cell
2

(1) When H2 molecule comes contacts platinum
catalyst, it splits into two H+ ions and two
electrons (e-)
(2) Make their way through the external circuit
(doing useful work such as turning a motor) and
return to the cathode side of the fuel cell

1

(3) O2 forms two oxygen atoms, each with a strong
negative charge
Negative charge attracts the two H+ ions through
the membrane
Combine with an oxygen atom and two electrons
from the external circuit to form a water molecule
(H2O)

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Electrochemical reactions involved in DMFC

Anodic reaction(Oxidation):
CH3OH + H2O

0.03 V

CO2 + 6H + + 6e-

Cathodic reaction (Reduction): 1.22 V
3/2 O2 + 6H+ + 6e3H2O
Overall reaction:
CH3OH + 3/2 O2

(Silva at al. 2005)

1.19 V

CO2 + 2H2O


Direct Methanol Fuel Cell
 Pt catalyst have highest activity for MeOH
oxidation thus far
 Ru enhances MeOH catalytic activity
OH- forms at lower voltage

 CO blocks sites on Pt surface, Ru helps
oxidize to CO2


Direct Methanol Membrane Fuel Cell
 Advantages:
 Direct fuel conversion – no reformer needed, all positive
aspects of PEMFC
 CH3OH – natural gas or biomass
 Existing infastructure for transporting petrol can be
converted to MeOH

 Problems:
 High catalyst loading (1-3mg/cm2 v. 0.1-0.3 mg/cm2)
 CH3OH hazardous
 Low efficiency (MeOH crossover – lowers potential)


Direct Methanol Membrane Fuel Cell
 Solving the Crossover Dilemma
 Alter thickness of polymer membrane

 Thinner = decreases ion flow resistance
 Thicker = decreases MeOH crossover
 Cs+ doped membranes
 Tricolli, University of Pisa, 1998
 Lower affinity for H2O
 MeOH tolerant cathodes
 Mo2Ru5S5 – N. Alonso-Vante, O. Solorza-Feria
 Higher oxygen reduction activity in presence of
MeOH
 (Fe-TMPP)2O – S. Gupta, Case Western, 1997
 High oxygen reduction, insensitive to MeOH