With reference to ‘fuel cells’ in which hydrogen-rich fuel and oxygen are used to generate electricity, consider the following statements:
1. If pure hydrogen is used as a fuel, the fuel cell emits heat and water as by-products.
2. Fuel cells can be used for powering buildings and not for small devices like laptop computers.
3. Fuel cells produce electricity in the form of Alternating Current (AC).
Which of the statements given above is/are correct?

The correct option is 1 only.

A fuel cell is an electrochemical device that converts the chemical energy of a fuel (such as hydrogen) and an oxidizing agent (such as oxygen) directly into electricity. Let us analyze each statement to understand why only the first statement is correct:

Statement 1 is correct:
When pure hydrogen is fed into a fuel cell alongside oxygen, an electrochemical reaction occurs. The hydrogen molecules react with oxygen molecules to generate electricity, with the only by-products being water and heat. The overall chemical equation representing this process is:

$$2H_2+O_2\to 2H_{2}O+\text{Electricity}+\text{Heat}$$

Since no carbon-based elements are involved when using pure hydrogen, there are zero carbon emissions, making it an extremely clean source of energy.

Statement 2 is incorrect:
Fuel cells are highly scalable and versatile. While they are indeed used for stationary power applications like powering buildings, they can also be scaled down for portable applications. This includes powering small consumer electronic devices such as laptop computers, smartphones, and military equipment.

Statement 3 is incorrect:
Like batteries, fuel cells produce electricity through electrochemical reactions that generate a continuous, one-directional flow of charge. Therefore, fuel cells inherently produce Direct Current (DC), not Alternating Current (AC). If the generated electricity needs to be fed into the power grid or used for standard household appliances, an inverter must be used to convert the DC to AC.