What is a fuel cell primarily designed to do?

A fuel cell is primarily designed to produce electrical energy from chemical reactions, specifically the reaction between a fuel (commonly hydrogen) and an oxidizing agent (often oxygen). In this process, the fuel undergoes oxidation, while the oxidizing agent is reduced, leading to the generation of electricity. This mechanism is highly efficient compared to traditional combustion engines, which convert energy through burning fuel, typically resulting in more energy loss as heat.

The other options touch on related concepts but do not accurately describe the primary function of a fuel cell. While producing water as a byproduct is a result of the reaction in some types of fuel cells, it is not their main purpose. Generating heat for power plants can occur in various energy systems, but this is not the objective of a fuel cell, which aims to maximize electrical output. Similarly, while fuel cells can work with stored fuels, they are not designed to function as storage devices; rather, they convert the energy stored in fuels into electricity during operation. Thus, the correct answer effectively encapsulates the primary role of a fuel cell in energy conversion.