Fuel cells generate energy through an electrochemical reaction. There's no combustion involved, as the fuel cell converts fuel directly to electricity and heat. There are several fuel cell technologies available. One of the most promising zero-emission technologies is the Proton exchange membrane fuel cell (PEMFC). The PEM fuel cell converts the chemical energy from hydrogen into electricity through an electro chemical reaction with oxygen, emitting only clean water and heat.
Fuel cells have higher efficiency than combustion engines, and the technology allows energy to be concentrated more densely than in petroleum fuels. If renewables are used to produce the hydrogen fuel, the entire energy chain will be clean, providing a true zero-emission fuel.
Learn more about the fuel cell potential for ships, including large ocean-going vessels