A fuel cell is a device that generates electricity by harnessing chemical reactions between a fuel and an oxidant. The most common type of fuel cell uses hydrogen as the fuel, which reacts with oxygen from the air to produce water and electricity. Fuel cells are considered a clean energy source because they do not emit greenhouse gases or other pollutants during operation. They have several potential applications, including powering vehicles, providing backup power for buildings, and generating electricity in remote locations where traditional power grids may not be accessible.