Hydrogen is the lightest element and the most abundant element by mass in the universe. As a gas at standard temperature and pressure, its atomic structure consists of a single proton and typically a single electron, granting it high reactivity and a low atomic mass. Chemically, it is capable of forming various compounds, and its role in energy conversion is significant, particularly when stored in chemical bonds. Because of its high energy density when combusted or used in reactions like those within fuel cells, hydrogen is extensively researched and utilized for various industrial applications and potential future energy storage systems.