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.

Which of the following statement is correct regarding hydrogen fuel cells?

The electricity production in fuel cells is higher than that in thermal plants

The correct answer is option 3. The electricity production in fuel cells is higher than that in thermal plants.

Let us break down each statement understand why option 3 is correct, and why the other options are incorrect.

1. This cell used the reaction between hydrogen and nitrogen to form ammonia (Incorrect)

This statement refers to the Haber process, which is used to produce ammonia (NH₃) by reacting hydrogen (H₂) with nitrogen (N₂):

\(N_2 + 3H_2 \longrightarrow 2NH_3\)

However, this is not what happens in a hydrogen fuel cell. A hydrogen fuel cell does not involve nitrogen at all. Instead, hydrogen fuel cells use the reaction between hydrogen (H₂) and oxygen (O₂) to produce electricity and water as the by-product:

\(2H_2 + O_2 \longrightarrow 2H_2O + \text{electricity}\)

Therefore, the statement is incorrect because hydrogen fuel cells use oxygen as the oxidant, not nitrogen.

2. Catalysts such as finely divided platinum on palladium metal do not have any effect on the rate of electrode reactions (Incorrect)

This statement is false because catalysts are essential in hydrogen fuel cells. The reactions at both the anode and the cathode are typically slow without a catalyst, and the use of catalysts, such as platinum (Pt) and palladium (Pd), significantly increases the rate of these reactions.

Role of Catalysts:

At the anode, hydrogen molecules (H₂) must split into protons (H⁺) and electrons (e⁻). This process is facilitated by a platinum catalyst, which speeds up the oxidation reaction:

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

At the cathode, oxygen (O₂) needs to combine with electrons and protons to form water (H₂O). Again, a catalyst like platinum helps in reducing oxygen efficiently:

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

Without these catalysts, the reaction rates would be much slower, leading to lower efficiency. Therefore, the statement is incorrect because catalysts have a major effect on the rate of the reactions in fuel cells.

3. The electricity production in fuel cells is higher than that in thermal plants (Correct)

This statement is true because fuel cells, including hydrogen fuel cells, are much more efficient than traditional thermal power plants. Let’s compare the two:

Hydrogen Fuel Cells:

In a hydrogen fuel cell, the chemical energy of hydrogen is directly converted into electrical energy through redox reactions. There is no need for intermediate steps such as burning fuel to produce heat, which is typical in thermal plants.

Fuel cells can achieve efficiencies of around 60-70% or higher in some cases. If combined with heat recovery (in combined heat and power systems), the efficiency can reach up to 85%.

Thermal Power Plants:

In thermal power plants, chemical energy from burning fuels like coal, natural gas, or oil is first converted into heat. This heat is then used to produce steam, which drives turbines to generate electricity. However, during this process, a lot of energy is lost due to heat dissipation, mechanical inefficiencies, and other factors. As a result, thermal plants typically operate at much lower efficiencies, around 35-40%.

Due to these factors, fuel cells produce more electricity from the same amount of fuel compared to thermal plants, making them more efficient. Therefore, this statement is correct.

4. The cell can run even when reactant supply stops (Incorrect)

This statement is false because hydrogen fuel cells require a continuous supply of reactants (hydrogen and oxygen) to function. The reactions in the fuel cell are dependent on the availability of both hydrogen (the fuel) and oxygen (the oxidant):

Hydrogen is oxidized at the anode, providing electrons.

Oxygen is reduced at the cathode, accepting electrons to form water.

If the supply of hydrogen or oxygen stops, the redox reactions can no longer occur, and the cell will cease to produce electricity. Therefore, without reactants, the fuel cell will stop working. Hence, this statement is incorrect.

Summary:

Option 1 is incorrect because hydrogen fuel cells use hydrogen and oxygen, not nitrogen.

Option 2 is incorrect because catalysts like platinum and palladium significantly improve the reaction rates in fuel cells.

Option 3 is correct because fuel cells have higher electricity production efficiency compared to thermal power plants, largely due to their direct energy conversion process.

Option 4 is incorrect because hydrogen fuel cells need a continuous supply of reactants to operate.

Thus, the correct statement is option 3: The electricity production in fuel cells is higher than that in thermal plants.