Direct Energy, 2018a

9 BATTERIES AND FUEL CELLS 235
9.5. A battery has specic capacity 252 C g
density is 2.245 m g . 3
and mass of 50 g. Its overall
(a) Find the specic capacity in mA·h g .
(b) Find the capacity in mA·h.
(c) Find the charge density in mA·h m 3 .
9.6. A battery has a specic capacity of 55 mA·h g and a nominal voltage
of 2.4 V. The battery has a mass of 165 g. Find the energy stored in
the battery inJ.
9.7. A battery has a sulfur cathode where the reactionS +2e − → S 2−
occurs. The anode is made from a mystery material, X, and at the
anode, the reaction X → X 2+ +2e − occurs. The theoretical specic
capacity of the sulfur reactionis 1.76 A·h g and the theoretical specic
capacity of material X is 0.819 A·h g . The theoretical specic capacity
of the materials combined is 0.559 A·h g . What is material X, and what
is V rp , the redox potential of the battery?
(Hint: Use a periodic table and a list of redox potentials.)
9.8. What is the dierence betweeneach of the items inthe pairs below?
• A battery and a fuel cell
• A primary battery and a secondary battery
• Redox potential and chemical potential
9.9. Consider the polymer electrolyte membrane fuel cell shown below.
The reactions at the electrodes are:
H 2 → 2H + +2e −
4e − +4H + + O 2 → 2H 2 O
Match the label in the picture to the component name.