Read the following passage given below and answer the question.

Production of electricity by thermal plants is not very efficient method. It is now possible to make cells in which reactants are fed continuously to the electrodes and products are also removed continuously. One of the most successful fuel cells is hydrogen fuel cell.

In Hydrogen fuel cell, which gas is undergoing oxidation?

Only hydrogen

The correct answer is option 1. Only hydrogen.

In a hydrogen fuel cell, the chemical reaction that generates electricity involves two processes: oxidation and reduction. Let us examine these processes and understand why only hydrogen undergoes oxidation while oxygen is reduced.

Key Concepts:

Oxidation is the loss of electrons.

Reduction is the gain of electrons.

These two processes occur simultaneously in an electrochemical cell, making it a redox (reduction-oxidation) reaction.

Working of Hydrogen Fuel Cell:

A hydrogen fuel cell consists of two main compartments:

Anode (Negative Electrode): This is where oxidation occurs.

Cathode (Positive Electrode): This is where reduction occurs.

Oxidation Process (At the Anode):

Hydrogen gas (H₂) is fed into the anode of the fuel cell. At the anode, hydrogen molecules are split into protons (H⁺) and electrons (e⁻). The hydrogen gas undergoes oxidation, which means it loses electrons. This can be represented by the following half-reaction:

\(\text{H}_2 \longrightarrow 2H^+ + 2e^-\)

The protons (H⁺) move through the electrolyte (a proton-conducting membrane) to the cathode, while the electrons (e⁻) travel through an external circuit, generating an electric current.

Thus, hydrogen gas (H₂) is the one undergoing oxidation because it loses electrons in this process.

Reduction Process (At the Cathode):

Oxygen gas (O₂) is fed into the cathode of the fuel cell. At the cathode, oxygen combines with the protons (H⁺) that have traveled through the electrolyte and the electrons (e⁻) from the external circuit. The oxygen gas undergoes reduction, which means it gains electrons. The reduction half-reaction is:

\(\text{O}_2 + 4H^+ + 4e^- \longrightarrow 2H_2O\)

This reaction forms water (H₂O) as a by-product, which is why hydrogen fuel cells are environmentally friendly, producing only water and no harmful pollutants.

Thus, oxygen gas (O₂) undergoes reduction, as it gains electrons in the process.

Why Only Hydrogen Undergoes Oxidation:

Hydrogen is the fuel in the hydrogen fuel cell, and it undergoes oxidation because it loses electrons. Oxygen acts as the oxidizing agent and undergoes reduction because it gains electrons.

In an electrochemical process, oxidation and reduction always occur together:

At the anode, oxidation happens (hydrogen loses electrons).

At the cathode, reduction happens (oxygen gains electrons)

Therefore, in the hydrogen fuel cell:

Only hydrogen undergoes oxidation, while oxygen is reduced.

Summary:

In a hydrogen fuel cell, hydrogen (H₂) is oxidized at the anode, losing electrons and generating protons. Oxygen (O₂) is reduced at the cathode, gaining electrons and forming water. Since only hydrogen undergoes oxidation, the correct answer is option 1: Only hydrogen.