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, the reactants are bubbled through which electrodes?

Porous carbon electrodes

The correct answer is option 4. Porous carbon electrodes.

In a hydrogen fuel cell, the fundamental goal is to convert the chemical energy of hydrogen and oxygen directly into electrical energy through electrochemical reactions. The basic components of a hydrogen fuel cell include:

Anode (where hydrogen oxidation occurs)

Cathode (where oxygen reduction occurs)

Electrolyte (which conducts ions between the anode and cathode)

Electrode Materials:

Porous Carbon Electrodes (Correct Answer):

Role and Structure:

Porous carbon electrodes are widely used in hydrogen fuel cells due to their ability to support the catalyst and provide a large surface area for the reactions.The porosity of these electrodes allows for effective diffusion of the reactants (hydrogen and oxygen) to the catalyst sites. This ensures that the gases are uniformly distributed and can efficiently participate in the electrochemical reactions. The porous structure also helps in managing the water produced during the reaction, preventing flooding and ensuring proper cell operation.

Catalyst Support:

Platinum, the catalyst used in hydrogen fuel cells, is typically deposited onto the surface of the porous carbon electrodes. The platinum catalyzes the reactions at the anode and cathode:

At the anode: Hydrogen molecules are oxidized into protons and electrons:

\(H_2 \rightarrow 2H^+ + 2e^-\)

At the cathode: Oxygen reacts with protons and electrons to form water:

\(O_2 + 4H^+ + 4e^- \rightarrow 2H_2O\)

Benefits: Porous carbon electrodes provide a stable and conductive substrate for the catalyst while allowing for high surface area contact with the reactants. They also help in efficient gas and water management within the cell.

Saturated Calomel Electrode (Incorrect):

The saturated calomel electrode (SCE) is a type of reference electrode used in electrochemical experiments to measure the potential of other electrodes. It is not used as an electrode in hydrogen fuel cells.

Silver Electrodes (Incorrect):

Silver electrodes are not typically used in hydrogen fuel cells. Silver is not effective as a catalyst for the reactions in fuel cells and lacks the necessary properties to support efficient energy conversion.

Platinum Electrodes (Incorrect):

Platinum is indeed a crucial component because it acts as a catalyst for the hydrogen and oxygen reactions. However, platinum is usually applied to the surface of the porous carbon electrodes rather than being used as standalone electrodes. The actual electrode material in the fuel cell is typically porous carbon, which supports the platinum catalyst. Thus, platinum itself is not the primary material used for the electrode but is critical as a catalyst.

Summary:

In a hydrogen fuel cell, the electrodes are made of porous carbon. These electrodes:

Provide a large surface area for the catalyst (platinum) to facilitate the reactions.

Allow for the effective diffusion of reactants to the catalyst sites.

Help manage the water produced during the reaction.

Thus, porous carbon electrodes are essential for efficient operation and performance of hydrogen fuel cells. Therefore, the correct answer is option 4: Porous carbon electrodes.