Page 90 - MODERN ASPECTS OF ELECTROCHEMISTRY

Direct Methanol Fuel Cells
n exp 2 _ n exp 4 _ 73
ε = = = 33.3% or ε = = = 66.6%,
F 6 F n 6
n th th
and to an overall efficiency:
ε= ε × ε E × ε F ≈ 13.3% or ε = ε rev × ε × ε F ≈ 26.6%. (16)
E
rev
3. Challenges in Developing DMFCsA
From the above discussion, it is clear that the main objectives of funda-
mental investigations on the direct methanol fuel cell are to:

decrease the overvoltages η i ,and hence to increase the reaction rates
at both the methanol anode and the oxygen cathode,
increase the reaction selectivity toward complete oxidation to CO 2,
find methanol-tolerant oxygen cathodes (e.g., transition metal macro-
cycles), and
decrease the effects of methanol crossover through the ionic mem-
brane by developing advanced membranes with optimum structures and
compositions.
These main objectives can be reached only by modifying the struc-
tures and compositions of primarily the anode (methanol electrode) and
secondarily the cathode (oxygen electrode) as discussed in Sections III
and IV, respectively. In addition, Section IV discusses the conception of
new proton exchange membranes with lower methanol permeability in
order to improve the cathode characteristics. Section V deals with the
progress in the development of DMFCs, while in Section VI the authors
attempt to make a prognosis on the status of DMFC R&D and its potential
applications.

III. ELECTRODE KINETICS AND ELECTROCATALY SIS OFA
METHANOL OXIDATION—ELECTROCHEMICAL AND
SPECTROSCOPIC INVESTIGATIONSA

1. IntroductionA
Methanol can be considered as a hydrogen carrier in a fuel cell. Conven-
tionally, methanol has been reformed/shift converted to produce hydro-
gen. A low concentration of carbon monoxide formed during this process
leads to a strong poisoning of the anode, and even after cleaning of the