The Foundations of Chemistry

21-25 The Hydrogen–Oxygen Fuel Cell 891

H 2 (g) + H 2 O(g)

2H 2 (g)  O 2 (g) → 2H 2 O(
)

Voltmeter O 2 (g) + H 2 O(g)

e

OH

OH

Anode
Porous graphite
plus catalyst

(a)

2H 2 (g)  4OH(aq) →
4H 2 O(
)  4e
Oxidation

OH

H 2 O

OH

H 2 O

K

K

K K

Container

e

H 2 (g) O 2 (g)

Cathode

Porous graphite

plus catalyst

O 2 (g)  2H 2 O(
)  4e →

4OH(aq)

Reduction

Figure 21-17 (a) Schematic drawing of a hydrogen–oxygen fuel cell. (b) A hydrogen–
oxygen fuel cell that is used in spacecraft.

(b)