Question

Which of the following species acts as reducing agent during working of hydrogen-oxygen fuel cell?

• A. $\text{H}_2$
• B. $\text{O}_2$
• C. $\text{H}^+$
• D. NaOH

Hint:

In fuel cells, the "fuel" (Hydrogen) is always oxidized (reducing agent) and "Oxygen" is always reduced (oxidizing agent).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
A hydrogen-oxygen fuel cell generates electricity through a continuous redox reaction between hydrogen gas and oxygen gas. A reducing agent is the substance that donates electrons to another substance, thereby undergoing oxidation itself.
Step 2: Key Formula or Approach:
Approach: Write out the electrochemical half-reactions occurring at the anode and cathode to identify which species is oxidized (loses electrons).
Step 3: Detailed Explanation:
Let's examine the half-reactions that occur in a hydrogen-oxygen fuel cell (using an aqueous base like NaOH or KOH as an electrolyte): At the anode (oxidation): \[ \text{H}_2(\text{g}) + 2\text{OH}^-(\text{aq}) \longrightarrow 2\text{H}_2\text{O}(\text{l}) + 2\text{e}^- \] Here, hydrogen gas ($\text{H}_2$) loses electrons (oxidation state changes from 0 to +1) and is oxidized. Therefore, $\text{H}_2$ acts as the reducing agent. At the cathode (reduction): \[ \frac{1}{2}\text{O}_2(\text{g}) + \text{H}_2\text{O}(\text{l}) + 2\text{e}^- \longrightarrow 2\text{OH}^-(\text{aq}) \] Oxygen gas ($\text{O}_2$) gains electrons (oxidation state changes from 0 to -2) and is reduced, acting as the oxidizing agent.
Step 4: Final Answer:
$\text{H}_2$ acts as the reducing agent.