Reactivity 1.3.5

Fuel Cells

Electrochemistry in action: Converting chemical energy directly to electricity.

Unlike combustion engines, fuel cells do not burn the fuel. They use redox reactions to generate a current.

Advantages

Disadvantages

Hydrogen is difficult to store (requires high pressure).
Most Hydrogen is currently made from Natural Gas (Steam Reforming), so it's not carbon-free yet.
Expensive catalysts (Platinum).

Anode (Oxidation):

H_2(g) + 2OH^-(aq) \rightarrow 2H_2O(l) + 2e^-

Cathode (Reduction):

\frac{1}{2}O_2(g) + H_2O(l) + 2e^- \rightarrow 2OH^-(aq)

Overall Reaction:

H_2(g) + \frac{1}{2}O_2(g) \rightarrow H_2O(l)

Putting it into Practice

Paper 2 Style

Direct Methanol Fuel Cells (DMFC) use methanol instead of hydrogen. The overall reaction is:

$CH_3OH + \frac{3}{2}O_2 \rightarrow CO_2 + 2H_2O$

Deduce the half-equation occurring at the Anode (Oxidation) in an acidic electrolyte.

[2 Marks]

Explain why a fuel cell is more efficient than an internal combustion engine.