Hydrogen is the most abundant element on earth, but it is always bound to something else. It’s found in common molecules like water, natural gas and plant material. Producing hydrogen means unlocking the chemical bonds in these molecules.

Most hydrogen is produced by reforming natural gas—passing super-heated steam through natural gas to break the chemical bonds in both compounds. Some hydrogen is produced by electrolyzing water—passing a current through water to break the chemical bonds. A few places are starting to use biogas (methane from landfills, wastewater treatment plants or decaying plant material) in a process that produces hydrogen, electricity and heat. Researchers are experimenting with ways to make hydrogen on a large scale using algae, microbes, bacteria and direct sunlight on water.

The illustration below shows the well-to-wheels energy efficiency, greenhouse gases and criteria pollutants when the hydrogen is produced in the two traditional manners—steam reforming and solar electrolysis—and used in a fuel cell vehicle.