THE ROLE OF THE

Fuel-Cell Chemistry Overview 153
H 2
H 2
H 2
e –
Porous Anode
e –
e – e –
To Vehicle Motor Drive
H +
(CF 2 CF 2 ) a
H +
external circuit. As a result of the current through the circuit, the oxygen will receive
two electrons and become negatively charged [4]. The cathode reaction is shown in
Equation 10.2:
+ −
O + 4H + 4e → 2H
O
2 2
(10.2)
Because positively charged protons are on one side of the membrane and negatively
charged oxygen ions are on the other, diffusion across the membrane will
occur [4]. At the cathode, water is formed and the overall reaction is
2H + O → 2HO+
electricity
(10.3)
2 2 2
(CFCF 2 ) b
PEM-type fuel cells have the advantage of operating at pressures from 101 to 810
kPa. In addition, they work well at lower temperatures (a feature not present in other
types of fuel cells). These fuel cells can operate at 55% efficiency versus a maximum
of 30% for internal combustion engines [1]. In order to achieve the necessary energy to
power the motors for propulsion, fuel cells are manufactured in a stack arrangement.
In these arrangements, other components are needed (such as humidifiers to keep
the cell moist, air compressors, and gas filters) to make up the fuel-cell propulsion
unit. Each stack has a flat cathode sheet and a flat anode sheet, which are stacked in
order to meet the particular vehicle’s power requirements [1]. Current vehicle testing
O
R f
SO 3 H
Perfluorosulfonic Acid
PEM Membrane
Anode RXN:
2H
Catalyst Catalyst
+ + 2e –
Cathode RXN:
O2 + 4H + + 4e – Overall RXN:
2H2 + O2 2H2O + electricity
2H2O FIgure 10.1 Diagram of fuel cell.
e – e–
Porous Cathode
e –
O 2
Q @ ~85 °C
H 2 O