Like electricity, hydrogen is a secondary source of energy. It stores and carries energy produced from other resources (fossil fuels, water, and biomass).

Hydrogen basics

What is hydrogen?

Each atom of hydrogen has only one proton. Hydrogen is also the most abundant element in the universe. The sun, and other stars, are essentially giant balls of hydrogen and helium gases.

On earth, hydrogen occurs naturally combined with other elements in liquids, gases, or solids. Hydrogen combined with oxygen is water (H₂O). Hydrogen combined with carbon forms different compounds—or hydrocarbons—that are found in natural gas, coal, and petroleum.

Hydrogen is an energy carrier

Energy carriers transport energy in a usable form from one place to another. Elemental hydrogen is an energy carrier that generally presents as two hydrogen molecules (H₂). Hydrogen can be produced, or separated, from a variety of sources—including water, fossil fuels, or biomass—and used as a source of energy or fuel. Hydrogen has the highest energy content of any common fuel by weight (about three times more than gasoline). However, it has the lowest energy content by volume as a liquid (about four times less than gasoline).

Producing hydrogen (by separating it from other elements) requires more energy than hydrogen provides when converted to useful energy. Despite this deficit, hydrogen is useful as a fuel due to its high energy content per unit of weight, which is why it is used as a rocket fuel and in fuel cells to produce electricity on some spacecraft. Although not widely used as a fuel now, it has significant potential for future use.

The U.S. Department of Energy's (DOE) Hydrogen Program has a number of participating offices and programs for hydrogen research, development, and deployment. One of the largest programs is the Regional Clean Hydrogen Hubs, sponsored by the Office of Clean Energy Demonstrations, to accelerate hydrogen use as an energy carrier for delivering and storing energy.

Hydrogen production

To use hydrogen, it first must be separated from the other elements it’s combined with in molecules. Hydrogen can be produced from many different sources and in various ways for use as a fuel. The two most common methods to produce hydrogen are steam-methane reforming and electrolysis (splitting water with electricity). Researchers are exploring other hydrogen production methods, or pathways.

Steam-methane reforming

Steam-methane reforming is the process used for nearly all commercially produced hydrogen in the United States. Commercial hydrogen producers and oil refineries use steam-methane reforming to separate hydrogen atoms from carbon atoms in methane (CH₄), the main component of natural gas. High-temperature steam (1,300°F to 1,800°F) under pressure reacts with methane with the help of a catalyst (a substance that speeds up a chemical reaction) to produce hydrogen, carbon monoxide, and a relatively small amount of carbon dioxide (CO₂).

Industrial facilities and petroleum refineries primarily use natural gas as the methane source for hydrogen production. Several fuel cell power plants in the United States treat and use landfill gas (biogas) as a hydrogen source. Biofuels and petroleum fuels are also potential hydrogen sources.

Electrolysis

Electrolysis splits hydrogen from water using an electric current. Electrolysis is commonly used in high school science classes to demonstrate chemical reactions and hydrogen production. On a large, commercial scale, the process is sometimes called power-to-gas, where electricity is power and hydrogen is gas. Electrolysis is a clean process, producing only hydrogen and oxygen, with no other byproducts or emissions. The electricity for electrolysis comes from the electric power grid, which is supplied with a mix of renewable sources, nuclear energy, and fossil fuels.

Other methods

Scientists are actively researching and developing new methods for hydrogen production, including:

• Thermochemical: Converting biomass into gas or liquids and then separating the hydrogen
• Photolytic: Using solar energy to split water into hydrogen and oxygen
• Biological: processes that use microbes, such as bacteria and microalgae, to produce hydrogen through biological reactions

Clean hydrogen production

The U.S. Department of Energy (DOE) supports source-neutral hydrogen production pathways, which means DOE does not use the color code others use to categorize hydrogen based on its source, production method, or carbon capture.

DOE's Hydrogen Program includes a number of programs for clean hydrogen production. Two of the major DOE initiatives are:

• The U.S. National Clean Hydrogen Strategy and Roadmap
• A clean hydrogen production standard

Use of hydrogen

Hydrogen has many current and potential uses

Hydrogen is used in industrial processes, as a rocket fuel, and in fuel cells for electricity generation and powering vehicles. Operators of several natural gas-fired power plants are exploring hydrogen as a supplement or replacement for natural gas. Hydrogen has the potential to indirectly store energy for electric power generation.

Hydrogen is used in industrial processes

Nearly all hydrogen consumed in the United States is used by the industrial sector for refining petroleum, treating metals, producing fertilizer and other chemicals, and processing foods. U.S. petroleum refineries use hydrogen to lower the sulfur content of fuels. Biofuel producers also use hydrogen to produce hydrotreated vegetable oil (HVO) for use as renewable diesel.

Hydrogen fuel cells produce electricity

Hydrogen fuel cells produce electricity by combining hydrogen and oxygen atoms. The hydrogen reacts with oxygen across an electrochemical cell—similar to a battery—to produce electricity, water, and small amounts of heat.

Fuel cells vary in size, type, and application. Fuel cell power plants provide electricity for individual facilities and have potential applications in microgrids and for remote locations that are not connected to electric power grids. Several vehicle manufacturers have developed fuel cells for powering vehicles.

Fuel cell power plants generate electricity (and heat, in a few cases), mostly as supplemental or backup power supply for individual buildings or facilities. As of the end of December 2025, the United States had about 186 operating fuel cell electric power generators with about 364 megawatts (MW) of combined nameplate electric generation capacity.¹ Most operating fuel cells use pipeline natural gas as the hydrogen source, but some fuel cell power plants will also use biogas from wastewater treatment, also known as landfill gas.

Hydrogen fuel cells power vehicles

Hydrogen is classified as an alternative vehicle fuel under the Energy Policy Act of 1992. The interest in hydrogen as an alternative transportation fuel stems primarily from its potential to power fuel cells in zero-emission vehicles (vehicles with no emissions of air pollutants). A fuel cell may be two to three times more efficient than an internal combustion engine running on gasoline. Several vehicle manufacturers have hydrogen fuel cell-vehicles. A few test vehicles are available to organizations with access to hydrogen-fueling stations.

The high cost of fuel cells and the limited availability of hydrogen fueling stations have limited the number of hydrogen-fueled vehicles in use today. Production of hydrogen-fueled vehicles is limited because people won't buy those vehicles if hydrogen refueling stations are not easily accessible, and companies won't build refueling stations if they don't have customers with hydrogen-fueled vehicles. The United States has about 52 hydrogen-vehicle fueling stations, all of which are in California. The State of California's Advanced Clean Cars Program includes assistance for establishing publicly accessible hydrogen-vehicle fueling stations throughout California to promote a consumer market for zero-emission fuel cell vehicles.

Hydrogen can be burned for electricity generation and heating

Burning hydrogen for electric power generation and for heating are potential uses of pure hydrogen or hydrogen-rich blends with natural gas. However, using hydrogen and hydrogen-blends in existing natural gas distribution infrastructure and combustion equipment poses several challenges related to materials compatibility and combustion characteristics. Some progress has been made with modifying natural gas burners in commercially available combustion turbines to accommodate high-hydrogen blends (up to 100% hydrogen), but continued research, development, and demonstration (RD&D) is needed before hydrogen will qualify for utility-scale power generation. Several power plants in the United States have announced plans to operate on a natural gas-hydrogen fuel mixture in combustion-gas turbines. One example is the Long Ridge Energy Generation Project in Ohio. RD&D is also needed to assess the compatibility of using hydrogen and hydrogen–natural gas blends in heating appliances.

Hydrogen can be used for energy storage

Hydrogen storage is an important technology for enabling hydrogen use across the U.S. economy. Hydrogen may be stored as a:

• Gas—Hydrogen can be stored as a gas in large volumes in natural geological formations—salt caverns, lined hard-rock caverns, depleted oil and natural gas fields, and aquifers. Gaseous hydrogen may also be stored in relatively smaller volumes in pressurized stationary or portable tanks and in dedicated hydrogen gas pipeline infrastructure. Gaseous storage is the most common and the most likely option for expanding hydrogen storage for most hydrogen use as an energy source.
• Liquid—Hydrogen can be liquefied by cooling it to below -423^oF (−253^oC). Liquefied hydrogen can be stored in super-cooled (cryogenic) tanks for transportation in fuel cell vehicles or directly as fuel in truck, rail, marine, and rocket engines. NASA has the two largest liquid hydrogen storage tanks in the world. Hydrogen liquefaction and cyrogenic liquid storage is an energy-intensive and expensive process.

Hydrogen could facilitate decarbonization of the electric power sector by storing energy produced using renewable resources for days or even weeks. Hydrogen could be produced with renewable resources when renewable energy production is high and could be stored to generate electricity when renewable resources are limited and electricity demand is high. One example is the Advanced Clean Energy Storage project in Utah, which plans to store large volumes of gaseous hydrogen produced from renewable resources for long-term seasonal energy storage. The H2DI Hydrogen Consortium also aims to provide support measures that will facilitate hydrogen storage, production, distribution, and demand.