2025 O Level Chem P1 Q26 — Electrochemistry / Hydrogen Fuel Cells Solution

Answer: A. In a hydrogen fuel cell, hydrogen gas is supplied at the anode and oxygen at the cathode. At the anode, \(\text{H}_2\) molecules are oxidised to release electrons: \(2\text{H}_2 \rightarrow 4\text{H}^{+} + 4\text{e}^{-}\). These electrons flow through the external circuit, providing the electrical current — i.e., generating electricity.

B and C describe reduction (gain of electrons) of hydrogen atoms or H₂ gas — this is the wrong direction; cells release electrons by oxidation of fuel, not by reduction of fuel.

D (combustion of hydrogen ions) is chemically meaningless — \(\text{H}^{+}\) ions don't combust. Combustion of hydrogen molecules happens, but combustion produces heat, not electricity directly. Fuel cells bypass combustion entirely by separating the oxidation and reduction half-reactions.