What is the most efficient source of energy?

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Instead of burning fuel like conventional engines, hydrogen fuel cells work through an electrochemical process. To produce electricity, hydrogen atoms are ionized on one side of an electrolyte membrane. While protons slip through, electrons must take the long way around through an external circuit, creating an electrical current as they move. Once the electrons reach the other side and pair off with the protons, the hydrogen combines with oxygen in the air, resulting in a little bit of heat and water as byproducts.