Page 38 - Introduction to Transfer Phenomena in PEM Fuel Cells

However, a temperature close to 1,000°C has certain disadvantages:
– the use of specific materials, resistant to this temperature, is vital;
– corrosion is rapid; Introduction to Hydrogen Technology 27
– very long start-up time;
– sensitivity to the variation in operating temperature;
– evacuation of heat.

1.2.1.7. Direct methanol fuel cell (DMFC)
The great potential for portable uses of fuel cells has generated enormous
interest for a fuel cell that can run directly on methanol. The direct methanol
fuel cell (DMFC) uses the same polymer membrane as the PEM fuel cell.
However, the fuel used in DMFC is methanol instead of hydrogen. Methanol
flows through the anode as fuel and it breaks down into protons, electrons,
water and carbon dioxide. The advantages of methanol are: it is available
everywhere, and it can easily be reformed from gasoline or biomass.
Although its energy density is only one-fifth of that of hydrogen per unit
weight, since it is in liquid form, it offers more than four times the amount of
energy per volume compared to hydrogen under a pressure of 250
atmospheres [BRU 99, HIR 98]. The chemical reactions that occur in this
fuel cell are:

– anode:

+
+
CH OH(liq) H O(liq) ⎯⎯→ CO + 6H + 6e − [1.16]
2
3
2
– cathode:
−
+
6H + 3 O + 6e ⎯⎯→ 3H O(liq) [1.17]
2 2 2
– overall reaction:
3
CH OH(liq) + O (g) ⎯⎯→ CO (g) 2H O(liq) [1.18]
+
3
2 2 2 2