The hydrogen-filled Hindenburg in 1936 or 1937. Photo from DeGolyer Library at Southern Methodist University.
THE HYDROGEN ECONOMY
The hydrogen economy is a hypothetical future in which energy can be bought, sold, stored, and transported in a currency of hydrogen, much like today’s energy is often exchanged in electricity. Because hydrogen doesn’t need to be attached to the electricity grid, it can be used in forms of transportation like buses and cars.
The end-user of the hydrogen, for example an automobile driver, doesn’t experience significant pollution beyond the formation of water from burning the hydrogen.
For more details about the hydrogen economy see here.
Hydrogen, a gas, isn’t a fuel like gasoline or coal; hydrogen is a way to store and transport energy made from other fuels, like a battery or electricity. Unlike fossil fuels, pure hydrogen isn’t stable, so forming hydrogen in the first place requires energy and produces carbon dioxide, and storing hydrogen involves special considerations because this light gas is very flammable and also quickens rust and oxidation in pipelines and storage containers.
HOW HYDROGEN IS DIFFERENT FROM FOSSIL FUELS
Allowing hydrogen (a gas) to burn in the presence of oxygen releases that stored energy in the form of heat. Hydrogen can also be reacted in a fuel cell to produce electricity. In either case, electricity or heat can then be used to power cars or any number of other devices. Gasoline, biofuels, wood, and other carbon-based fuels all produce carbon dioxide when they are burned, and rising carbon dioxide levels are widely implicated in climate change. Burning hydrogen produces energy, water and a few trace compounds, but it doesn’t produce carbon dioxide.
2 H2 (hydrogen gas) + O2 (oxygen gas) = 2 H2O (water vapor) + energy
It’s unclear what widespread emission of water vapor could do. According to recent published estimates, atmospheric water vapor is responsible for 75 percent of the greenhouse effect. However, water vapor can condense, and it’s naturally-occurring in the atmosphere. It is much easier to trap and transform to liquid than the carbon dioxide normally emitted by burning gasoline. Carbon dioxide won’t form a liquid at atmospheric temperatures and will solidify into dry ice only below -108.4 Fahrenheit, so proponents say it can be easier to trap the vapor in hydrogen-powered machines.
If the energy used to generate and purify and store and ship hydrogen doesn’t require emitting greenhouse gases or toxics, proponents argue that hydrogen is a clean alternative.
SOURCES OF HYDROGEN: THE UNFORTUNATE REALITY TODAY
Hydrogen, not carbon, is the most prevalent atom in the human body. There are two hydrogen atoms in every water molecule, and as many as hundreds of hydrogen atoms on the basic building blocks of life, from DNA to plant fibers. Nonetheless, harvesting the hydrogen atoms out of any of these structures to make hydrogen fuel isn’t easy because hydrogen likes to be bonded to carbon or oxygen; it doesn’t like to be elemental gas.
To produce pure hydrogen today, industries use primary fuel source like petroleum, natural gas, coal, or biomass. Through chemical processing, the hydrogen atoms are stripped from the fuel by way of an input of energy from electricity (more than 80 percent of which comes from fossil fuels in the United States). Furthermore, the leftover material from the stripping is carbon dioxide, the same carbon dioxide that would have been produced if the fuel was burned in an engine.
The reactions for various fuel to hydrogen conversions can be found on the U.S. Department of Energy website here.
Hydrogen can also be produced, at great energy loss, through the electrolysis of water: using electricity, water is divided into its constituents, hydrogen and oxygen. However, water electrolysis is the least carbon-neutral hydrogen production method, and it is very expensive ($3 to $6 per kilogram instead of a little more than $1 in the case of using coal for hydrogen), according to the U.S. Energy Information Administration. All hydrogen production methods result in a net energy loss.