State the half-equations for the reactions taking place at the negative electrode (anode) and the positive electrode (cathode) in an alkaline hydrogen-oxygen fuel cell.

Negative electrode (anode):

Positive electrode (cathode):

A different type of cell has the half-equation below.

\[{\text{L}}{{\text{i}}^ + }{\text{(polymer)}} + {\text{Mn}}{{\text{O}}_2}{\text{(s)}} + {{\text{e}}^ - } \to {\text{LiMn}}{{\text{O}}_2}{\text{(s)}}\]

Identify this type of cell.

Both fuel cells and rechargeable batteries offer great potential for the future. Compare these two power sources.

Suggest two problems associated with using hydrogen gas in a fuel cell.

Negative electrode (anode):

\({{\text{H}}_2}{\text{(g)}} + {\text{2O}}{{\text{H}}^ - }{\text{(aq)}} \to {\text{2}}{{\text{H}}_2}{\text{O(l)}} + {\text{2}}{{\text{e}}^ - }\);

Positive electrode (cathode):

\({{\text{H}}_2}{\text{O(l)}} + \frac{1}{2}{{\text{O}}_2}{\text{(g)}} + {\text{2}}{{\text{e}}^ - } \to {\text{2O}}{{\text{H}}^ - }{\text{(aq)}}\);

Allow correct equations involving multiple coefficients (i.e. 2H₂ etc.).

Ignore state symbols.

Allow e instead of e^–.

Award [1 max] for correct equations but at incorrect electrodes.

lithium-ion;

Allow rechargeable.

fuel cells need constant supply of reagents/chemicals (when they produce electricity)

while rechargeable batteries need occasional supply of electricity / OWTTE;

fuel cells fuel supplied continuously while in rechargeable batteries energy stored

inside the batteries / OWTTE;

products must be constantly removed from a fuel cell;

fuel cells (currently) more expensive;

fuel cells made of chemically more inert materials / OWTTE;

(potentially) explosive (gas) / flammable;

must be stored/transported in large/heavy containers;

Most candidates struggled with all parts of this question. Correct relevant equations at the electrodes were given by only a very few candidates in (a).

In (b) about half mentioned Lithium-ion.

In (c) many candidates were not able to compare fuel cells and rechargeable batteries. Some managed to score M1.

In (d) many candidates stated the H₂(g) is dangerous but did not explain why. Some scored M1, but no candidate scored the second mark regarding the storing and transporting of H₂(g).