Which device converts chemical energy from hydrogen into electricity through an electrochemical reaction, emitting only water?

• A. Battery
• B. Generator
• C. Fuel cell
• D. Turbine

Answer: (C)

The concept here is converting chemical energy directly into electrical energy through an electrochemical reaction. In a hydrogen fuel cell, hydrogen gas and oxygen from the air are fed to electrodes separated by an electrolyte. At the anode, hydrogen is oxidized, releasing electrons that travel through an external circuit to provide electricity, while protons move through the electrolyte to the cathode. There the protons, electrons, and oxygen combine to form water. This direct electrochemical process yields electricity with water as the main byproduct, making it a clean energy conversion method when hydrogen is the fuel.

This differs from other devices: a battery stores and discharges energy via internal chemical reactions without needing a continuous external fuel supply; a generator converts existing mechanical energy into electricity; and a turbine converts fluid energy into mechanical energy (which is then turned into electricity by a generator). The fuel cell stands out because it turns chemical energy of hydrogen directly into electrical energy through an ongoing electrochemical reaction.