Hydrogen

Hydrogen is an important means to replace fossil fuel in several industries

Hydrogen, the smallest and most abundant element in the universe, is critical to decarbonizing the global economy. Hydrogen is an energy carrier that can be produced with clean energy and replace fossil fuels in a range of industrial processes. Importantly, hydrogen produces no direct greenhouse gasses when used.

Hydrogen, or hydrogen-derived fuels, will allow the replacement of some of the world's dirtiest vehicles. For many vehicle types, such as automobiles, electrification is the clear path to decarbonization. Yet there are many vehicles, namely planes and ships, where electrification is not a viable strategy due to batteries' low energy density by weight and volume. Instead, hydrogen or hydrogen derived fuels are the likely solution.

Hydrogen can be used as a fuel in a variety of ways. Hydrogen can be burned in engines, similar to existing fuels, with the only byproducts being water vapor and a very small quantity of nitric oxides (NOx), which is a pollutant but not a greenhouse gas. Alternatively, hydrogen can be used without greenhouse gas emissions to produce other fuels, such as ammonia and methanol, that can be used as a liquid fuel. Both ammonia and methanol have much higher volumetric energy densities than liquid hydrogen. Both ammonia and methanol also have milder liquefaction requirements and are easier to store and transport than liquid hydrogen. Hydrogen fuel cells, which produce electricity through a chemical reaction rather than combustion, can drive electric motors and are another option for powering planes and ships. Fuel cells are more efficient than traditional combustion engines and produce no pollutants when used.

Hydrogen derived chemicals will also be essential for other parts of the energy transition. Ammonia produced using greenhouse gas emitting processes is widely used in fertilizer production. These production processes must be converted to non-emitting processes using clean hydrogen. Methanol is used to produce a wide range of chemicals, and its production process must also be converted to non-emitting processes using clean hydrogen.

Hydrogen can be used to replace fossil fuels in industrial processes where electrification is not an option. Hydrogen can be used to produce intense heat, which makes it useful for industrial applications such as steel production. The ability to store and transport hydrogen, combined with its high energy density, allows for it to be used flexibly across different industrial settings.

Hydrogen will be used as a form of seasonal energy storage. Hydrogen can be produced with clean energy and stored — for example, in large quantities in underground salt caverns. Later, the stored hydrogen can be reconverted into electricity in power plants. Salt cavern storage is one of the few available energy storage methods that can store large amounts of energy for long periods of time without significant energy losses — making it one of the few large-scale options for seasonal energy storage.

In recent years, substantial progress has been made in the financial and technical viability of technologies that produce and utilize hydrogen. In response, there is both great enthusiasm and widespread skepticism regarding hydrogen's potential. Skepticism and caution are valid. Just because hydrogen can replace fossil fuels in an area does not mean it is the safest or most efficient option. There are many applications for which enthusiasm is unwarranted and where hydrogen should not be used — for example, home heating and automobiles — because cleaner, safer, and more efficient solutions are available. There are other applications for which skepticism is overblown or where hydrogen is likely the only viable alternative to fossil fuels — such as aviation. This document aims to discern which proposed hydrogen end-uses are worth pursuing and which are not.

Switching to hydrogen for any application poses formidable challenges. It requires huge amounts of electricity and water to produce and store at large scales. As the smallest atom in the periodic table, it is common for hydrogen to leak during production and use. Though not a direct greenhouse gas, when it is released into the atmosphere it causes secondary effects that effectively make it an potent indirect greenhouse gas. Every effort must be made to limit the leakage of hydrogen. Though difficult, this is an engineering challenge that can be solved. Leakage rates are already less than 1% in some settings. As long as the leakage rate is relatively low, the emissions benefits of hydrogen over fossil fuels, in appropriate settings, are not in dispute.

Green hydrogen is the only clean form of hydrogen production

Hydrogen is highly reactive and thus rarely found in its pure form in nature. Instead, hydrogen must be extracted from compounds such as water (H2O) or methane (CH4). There are several methods to produce pure hydrogen using different technologies and energy sources, most of them producing greenhouse gas emissions. The hydrogen industry uses a color coding system to differentiate between types of hydrogen production. The following table lists some of the common types of hydrogen production.

Hydrogen Production Methods

Hydrogen Color Code	Production Method
Green	Green hydrogen is produced through the electrolysis of water powered by clean energy sources.
Gray	Gray hydrogen is produced through steam methane reforming, where hydrogen is separated from methane. Releases considerable carbon dioxide (CO2) emissions.
Blue	Blue hydrogen is also produced through steam methane reforming but uses carbon capture technology to attempt to capture CO2 and prevent it from reaching the atmosphere.
Black (sometimes called brown)	Black hydrogen is produced through gasification, where coal is converted into hydrogen and carbon monoxide. This process also releases very considerable amounts of CO2.
Pink	Pink hydrogen is produced through the electrolysis of water powered by nuclear energy. Some consider this to be a subset of green hydrogen. In the context of this wiki, we will consider electrolysis powered by electricity from nuclear energy to be a type of green hydrogen.
Turquoise (sometimes called red)	Turquoise hydrogen is produced through the methane pyrolysis process, which breaks methane into hydrogen and solid carbon, avoiding CO2 emissions if the carbon byproduct is permanently sequestered or used beneficially. This technology is still in development and not used commercially.
White	White hydrogen is naturally occurring hydrogen. Large deposits of naturally occurring hydrogen have been found underneath the earth’s crust, but there is currently no way to extract this hydrogen for commercial use.

Of the most commonly used forms of hydrogen production — gray, blue, and green — only green hydrogen does not result in any greenhouse gas emissions and can be considered a form of clean hydrogen.

Gray hydrogen is produced using steam methane reforming (SMR). SMR is a process where methane reacts with steam to produce hydrogen and carbon dioxide (CO₂). The hydrogen is captured for future use and the CO₂ is vented into the atmosphere. Additionally, methane leaks occur during the production and transportation of methane, further increasing the emissions associated with gray hydrogen. Gray hydrogen is currently the predominant form of hydrogen production in the United States.

Blue hydrogen is also produced using SMR but incorporates carbon capture and storage (CCS) technologies to capture and store the CO₂ byproduct. Existing carbon capture technology captures only around 60% of the CO2 produced during SMR, and the rest of the CO2 is released into the atmosphere. Blue hydrogen also does not address the problem of methane leakage. Although blue hydrogen produces fewer emissions relative to gray hydrogen, it is still a dirty form of hydrogen production that contributes to climate change.

Green hydrogen is produced through electrolysis, where electricity splits water into hydrogen and oxygen using an electrolyzer. If the electricity comes from clean energy sources, green hydrogen production creates no greenhouse gas emissions. Green hydrogen production is a clean alternative that does not contribute to climate change.

Despite there being no emissions during green hydrogen production, the process still requires careful regulation to ensure it is a net positive for the climate. Many climate organizations advocate for the "three-pillars" approach of additionality, time matching, and geographic deliverability. However, once the U.S. grid runs on 100% clean energy, the three pillars approach will no longer be necessary.

The United States must scale a domestic electrolyzer industry

The domestic manufacturing of electrolyzers must grow to support the American hydrogen economy. Electrolyzers are machines that use electricity to split water into hydrogen and oxygen and are the core technology in green hydrogen production. Currently, American manufacturers produce only a small amount of electrolyzers in relative and absolute terms. Although investment in new electrolyzer production capacity has grown in recent years, it remains considerably smaller than in other clean technology industries. To create a thriving green hydrogen economy, the United States must first create a new industrial policy strategy to support the growth of domestic electrolyzer manufacturing.

A robust domestic electrolyzer industry is necessary to reduce the costs of green hydrogen production. Existing American electrolyzer manufacturers have yet to tap into the benefits of economies of scale that come with mass production. As domestic producers expand their operations, the cost of electrolyzers will likely fall considerably. This reduction in electrolyzer costs will lower the capital investment required for new green hydrogen projects and make hydrogen more competitive with fossil fuels. Furthermore, a reliable domestic supply chain for electrolyzers will mitigate the impact of supply chain disruptions and international market fluctuations on green hydrogen developers.

Scaling the domestic electrolyzer industry will create a supply of electrolyzers better suited to the specific needs of the American hydrogen economy. Different types of electrolyzers offer distinct advantages and disadvantages. The two most common types are alkaline electrolyzers and Proton Exchange Membrane (PEM) electrolyzers. Alkaline electrolyzers are cheaper to manufacture but have long start-up times, making it difficult to align hydrogen production with intermittent renewable energy sources. In contrast, PEM electrolyzers are more expensive but have significantly faster start-up times, making them better suited for integration with the American energy grid. Currently, PEM electrolyzers are less common than alkaline electrolyzers, but developing a robust American electrolyzer industry could help meet this demand and optimize hydrogen production for the U.S. market.

Expanding the domestic supply of electrolyzers requires overcoming a difficult Catch 22 situation. Many electrolyzer manufacturers are forgoing investments in new manufacturing capacity due to a lack of demand for green hydrogen. In fact, many electrolyzer manufacturers are already operating below their capacity and producing fewer electrolyzers than anticipated due to a lack of orders. At the same time, green hydrogen producers are delaying new investments in part because there are difficulties with obtaining affordable electrolyzers. Resolving this stand-off will require proactive government policies to help coordinate a simultaneous electrolyzer supply and demand expansion.

The United States has a small window of opportunity to expand its electrolyzer industry. China and the European Union have surpassed the United States in electrolyzer production. If policymakers and investors do not act now, the gap between the U.S. and its peers may be too large to overcome, leaving American hydrogen producers reliant on foreign producers indefinitely.

Though hydrogen acts indirectly as a greenhouse gas in several ways, hydrogen emissions can be kept extremely low in both production and use

Hydrogen, the smallest element in the universe, must be handled carefully to ensure it does not leak into the atmosphere and contribute to global warming. Hydrogen itself is not a greenhouse gas, but can indirectly contribute to global warming in a few ways if it escapes into the atmosphere. Hydrogen interacts with hydroxyl radicals (OH), which play a vital role in the breakdown of atmospheric methane, a potent greenhouse gas. By reducing the availability of hydroxyl radicals, atmospheric hydrogen can indirectly increase the lifetime and concentration of methane in the atmosphere. Hydrogen increases the formation of ozone (O₃) in the atmosphere when it interacts with nitrogen oxides (NOx) and other compounds. Ozone in the lower atmosphere is a powerful greenhouse gas. When hydrogen reaches the stratosphere, it can oxidize to form water vapor. Water vapor in the stratosphere can trap heat and contribute to the greenhouse effect.

The primary way industrial hydrogen reaches the atmosphere is through accidental leakage. From production to end-use, every stage of the hydrogen lifecycle presents risks for leakage that must be addressed. During production, small amounts of hydrogen may escape from electrolyzers. Storage systems, particularly above-ground tanks that store compressed or liquid hydrogen, can develop leaks over time. Transporting hydrogen long-distances can degrade the integrity of pipelines and transport vessels. Furthermore, most end-use applications of hydrogen can also be sources of leakage if not properly managed.

Hydrogen producers and consumers can take proactive measures to keep hydrogen leakage low. It is possible to produce, transport, store, and use hydrogen in steel production, fuel cells, and jet engines with low levels of hydrogen emissions through investments in high-quality infrastructure and proper maintenance. Policymakers must discourage the use of hydrogen in industries where leakage is inherently high and where more efficient or safer options exist, such as home heating. Studies have also consistently shown that even low levels of leakage do not outweigh the climate benefits of green hydrogen production.

Every country will need to produce their own green hydrogen, primarily in facilities near end users

Every country must develop its own hydrogen production capacity to guarantee a reliable hydrogen supply for domestic use. Most countries are home to at least one manufacturing industry that will require hydrogen to decarbonize, such as steel production, or industries that currently rely on dirty hydrogen such as fertilizer and chemical production. Additionally, every country has airports or ports that will require a supply of hydrogen or ammonia for refueling purposes.

Some countries are already looking to import hydrogen instead of producing it locally, but this approach poses several challenges. Hydrogen is difficult to transport due to the requirements of liquid and compressed hydrogen storage. Moreover, the risk of leakage is uniquely high when transporting liquid hydrogen, as any heat ingress could lead to substantial leakage.Furthermore, reliance on imported hydrogen creates a dependency on external suppliers, which could lead to supply chain vulnerabilities.

Given these considerations, most hydrogen should be produced in small, distributed facilities close to end users. Building hydrogen near end users significantly reduces both capital and operational expenses associated with transportation by reducing the need for new infrastructure. Additionally, producing hydrogen near its point of use minimizes the risk of leakage and energy losses during transport.

Major global economic powers such as the United States can use their considerable influence and resources to help nations develop their own hydrogen production capacity during the transition. Countries that do not invest in hydrogen production will risk falling behind competitors and facing supply chain vulnerabilities.

Hydrogen is needed to make cleaner primary steel

Hydrogen will play a vital role in decarbonizing primary steel production. The global steel industry is responsible for around 7% of yearly emissions, and the largest source of the industry’s emissions comes from primary steel production. Primary steel production is the process of creating new steel from iron ore mined from the earth. Although steel made from recycled scrap continues to make up a larger and larger share of the steel market, especially in the United States, primary steel production remains the predominant form of steel production in the world.

The majority of primary steel production is done using highly-polluting coal-powered blast furnaces. Hydrogen can eliminate the need for these coal-powered blast furnaces through a process known as hydrogen Direct-Reduction Iron (DRI). DRI can eliminate most greenhouse gas emissions from primary steelmaking without compromising production capacity.

Primary steelmaking will remain an essential part of the steel industry for the foreseeable future. Steel made from recycled scrap metal is becoming more common but will not replace the need for new primary steel. The supply of scrap steel is highly variable and depends on the recycling rates of consumer products throughout the year. Additionally, specific applications, such as automotive manufacturing and construction, require the high quality and particular properties only primary steel can provide. The need for primary steel will continue to increase as the world decarbonizes, as many clean energy technologies require large amounts of steel.

Other clean steel technologies may emerge in the coming years that require less energy or infrastructure investment than hydrogen DRI. For example, the steel producer Boston Metals has developed a promising process to make clean steel without hydrogen. However, it is still unclear whether this process can scale to the levels required by industry and construction. Until better technologies than hydrogen for steelmaking are proven, we must continue to develop and invest in hydrogen-based clean steel.

Hydrogen is likely the best or only way to power large, long-haul jets

Perhaps the most controversial use of hydrogen is for aviation. Many experts are understandably skeptical about hydrogen-powered aircraft because of hydrogen’s flammability, lower energy density relative to jet fuel, the danger of leakage, and the creation of high-altitude water vapor from burning hydrogen. Though hydrogen has powered aircraft since the 1950s, doing so safely and efficiently enough for large-scale passenger travel remains a challenge. Though it will require epic engineering projects on the scale of NASA’s moonshot, new aircraft designs will likely be able to safely accommodate the large fuel tanks needed for hydrogen, improvements in liquid hydrogen storage will reduce the size and weight of fuel tanks while keeping leakage to a minimum, and high-efficiency hydrogen engines could reduce the quantity of necessary onboard fuel.

Hydrogen fuel is likely best suited for large, long-haul jets for two reasons: first, efficiency of liquid hydrogen fuel storage increases with volume; and second, future improvements in battery performance may make 100% electric short flights by smaller jets possible in the near future, which would be preferable to hydrogen. As of now, hydrogen is our best hope for minimizing emissions of long haul flights of large numbers of passengers between major cities. If atmospheric carbon removal technologies can not remove the CO2 produced by aviation and other difficult-to-abate sources, then we may be faced with the choice between hydrogen aviation or no flying at all.

Today, many experts see “sustainable aviation fuels (SAFs) as the future of clean aviation. SAFs are a broad category of fuels made from alternative sources, such as biomass, waste materials, or synthetic processes, that reduce greenhouse gas emissions compared to conventional jet fuels. Unfortunately, despite receiving billions in investments and support from major airlines, SAFs are a false solution. For one, SAFs still release greenhouse gasses into the atmosphere when they are burned. Furthermore, the mass production of sustainable aviation fuels requires enormous quantities of land for growing crop feedstocks. If attempted on a scale large enough to fuel current levels of flying, acquiring the land to produce SAF feedstocks will contribute to deforestation and the destruction of important carbon sinks, which may result in SAF’s having higher lifecycle emissions than traditional jet fuel.

Proponents of sustainable jet fuel may argue that the overall requirements of powering all large jets with hydrogen are just as impractical as the challenge of massively scaling a sustainable jet fuel industry. This is an argument worth considering because the challenges of scaling hydrogen production to the levels that will be required are also enormous. Those challenges, however, are solvable with century-old technology that is already operating at scale, with only scaling and engineering improvements necessary. The challenge of making point source carbon capture and direct air capture work at the incredible scales that are needed will require, on the other hand, efficiency improvements and engineering feats that may turn out to be impossible over the coming decades. We should continue every effort to improve carbon capture technology — but the future of clean aviation should not be put on hold for a technology that may not emerge.

The vast green electricity needs of hydrogen production for aviation can be solved by a plan for expanding clean grid capacity such as the one presented by the Mission for America’s national mission for clean power. The comprehensive approach of the Mission for America is part of what makes hydrogen a scalable and practical fuel demanding application such as aviation.

Hydrogen will be used to produce green ammonia to power shipping vessels

Hydrogen will play a key role in decarbonizing the global shipping industry, which is responsible for 3% of global greenhouse gas (GHG) emissions. There is widespread debate on the future of clean shipping, with every proposed solution still in the earliest stages of implementation. Most experts believe large shipping vessels can not be electrified and instead will require a new clean liquid fuel to replace existing bunker fuels. Some experts propose using liquefied natural gas, but this is an unacceptable choice due to high production and end-use greenhouse gas emissions. Of the remaining commonly proposed fuels, three leading contenders are methanol, liquid hydrogen, and ammonia.

Each of these fuels has advantages and disadvantages. Ammonia, however, emerges as the best path forward when assessed based on climate impacts, energy density, onboard infrastructure, and onshore infrastructure.

Climate: Of the three proposed fuels, only methanol produces greenhouse gasses when burned. Ammonia and liquid hydrogen produce no GHG emissions when burned but do emit nitrogen oxides (NOx), a pollutant that can indirectly impact global warming. NOx emissions from burning ammonia can be reduced by attaching a selective catalytic reduction (SCR) system to the ammonia engine.

Energy density: Volumetric energy density is a key consideration because it determines how much energy can be stored in a given fuel volume. Fuels with higher volumetric densities generally require less storage space on ships. All three proposed fuels have lower volumetric energy densities than bunker fuel, necessitating trade-offs in cargo space or additional refueling stops. Ammonia has a higher volumetric energy density than liquid hydrogen but is slightly lower than methanol. The difference in energy density between ammonia and bunker fuel can be managed with minor modifications to cargo capacity or additional bunkering stops.

Onboard infrastructure: Ammonia, methanol, and liquid hydrogen require upgrades in the ship infrastructure. Ammonia and methanol generally require straightforward retrofitting of existing engines and fuel systems, easing integration into current ships. In contrast, liquid hydrogen demands more advanced and costly storage solutions to maintain cryogenic temperatures.

Onshore infrastructure: Ammonia likely requires the least new infrastructure to meet demand. Liquid hydrogen necessitates significant investments in handling and transportation infrastructure, including cryogenic storage and specialized pipelines or trucks to prevent leakage. Liquefying hydrogen also consumes a substantial amount of electricity—more than is needed to produce and liquefy one kilogram of ammonia. Producing clean methanol demands extensive infrastructure investments, primarily because its production requires a source of carbon from direct air capture (DAC). There are no large-scale DAC systems in the United States, and DAC systems are expensive and require substantial electricity. In contrast, ammonia production is a simple industrial process, and ammonia is already frequently transported by road and sea.

In evaluating climate impacts, energy density, and both onboard and onshore infrastructure requirements, ammonia emerges as the most balanced and feasible option for decarbonizing the shipping industry. Its acceptable energy density and relatively low infrastructure demands make it the strongest candidate for replacing bunker fuels.

Transitioning to ammonia-powered ships will require a global effort to build ammonia refueling infrastructure at major ports. Long-haul trade routes, particularly transoceanic trips, need reliable refueling stations. Shipping operators will not begin transitioning to ammonia ships unless they are confident that there is a reliable supply of ammonia for them to refuel with.

The U.S. must play a large role in building the refueling infrastructure to support ammonia shipping. The U.S. could coordinate with key trading partners to develop ammonia refueling infrastructure at their ports through investment and technology sharing initiatives. The United States could also help lead the transition by investing heavily in a domestic ammonia-powered merchant marine fleet of its own, thereby demonstrating the viability of ammonia-powered ships.

Hydrogen can be used as seasonal energy storage

Hydrogen will play a crucial role in decarbonizing the power grid as a form of energy storage. Compressed hydrogen can be stored in underground salt caverns, which can hold large volumes of high-pressure gasses for long periods. Salt caverns provide an ideal environment for hydrogen storage due to their natural impermeability, which reduces the risk of leaks to nearly zero. Salt caverns have long been used to store hydrogen and other hydrocarbons.

Hydrogen energy storage will help stabilize the grid and reduce America's dependence on fossil fuels. The caverns' ability to maintain the integrity of stored hydrogen over extended periods with no energy losses makes them one of the few viable options for seasonal energy storage — an essential component of a 100% clean energy grid. Hydrogen will be produced when clean energy generation is abundant, stored in the cavern, and turned back into clean electricity when supply is low. Salt cavern hydrogen storage is one of the only forms of energy storage that can store substantial amounts of power for months without any energy losses. Hydrogen stored in salt caverns can quickly be called upon in emergencies, making it an ideal replacement for fossil fuel peaker plants.

The United States can produce enough green hydrogen to decarbonize key industries

Building a hydrogen economy on the scale proposed in this document will require vast resources — both financial and physical — but is possible in the context of the Mission for America. There are four significant resource constraints that may restrain green hydrogen production: finding investors for a project, acquiring electrolyzers, securing enough water for production, and purchasing enough electricity. Securing the necessary investment and electrolyzers is primarily a political and economic challenge, not a physical one. However, the supply of water and electricity will be real constraints on hydrogen production and it is necessary to evaluate if it is possible to meet these needs.

To prove the viability of large-scale hydrogen production, we attempted to quantify the water and electricity requirements of producing enough hydrogen to support a domestic hydrogen aviation industry. We chose hydrogen aviation as our case study because the aviation industry is likely to become the largest consumer of hydrogen in a future net-zero America. If it is possible to produce enough hydrogen to support the aviation industry, then the same should be true of other industries that need significantly less hydrogen.

We attempted to establish a rough estimate of how much hydrogen would be needed to support a hydrogen aviation industry, and found that it would require around 27 million tons of hydrogen per year. To be clear, this should only be taken as a rough estimate.

Green hydrogen production demands significant water for electrolysis and industrial cooling. Moreover, the water for electrolysis must meet strict quality standards, and hydrogen producers often discard a lot of water in production. On average, we found that hydrogen producers must withdraw about 47 liters of water to produce one kilogram of hydrogen. Producing enough hydrogen to decarbonize the aviation industry would require around 1.3 trillion liters of water. This may sound like a lot, but it is equivalent to less than 1% of yearly water usage in the United States.

Producing and utilizing hydrogen will require a sizable amount of new clean energy generation on the grid. Producing one kilogram of hydrogen requires around 50 to 55 kWh of electricity. Preparing hydrogen for transportation and use will also require a significant amount of electricity. Compressing hydrogen requires little energy, only 2.7 to 6.4 kWh per kilogram, but liquefying hydrogen requires a substantial 11.9 to 15 kWh per kilogram. Producing 10 million tons of hydrogen would require 525 billion kWh of electricity — equivalent to around 12% of the American power grid. Producing and liquefying enough hydrogen to support a hydrogen aviation industry would require 1.78 trillion kWh of electricity — equivalent to 48% of the existing American power grid.

On the one hand, increasing electricity production for this one application can feel ridiculous. On the other hand, ending aviation feels inconceivable. The truth is, we will need to double total electricity production and then double it again everywhere in the world to meet the needs of electrifying industry, homes, buildings, and transportation, large-scale direct air capture, and the exponentially increasing demands of computing data centers AI and other applications. With or without hydrogen aviation, we need a new approach to electricity production that essentially provides unlimited supply. As explained in the Mission for America clean power plan, this can be achieved by the continued expansion of distributed and centralized renewables, the addition of enhanced geothermal, and the development of new large-scale nuclear programs. On top of increasing production, deep gains in energy efficiency can be made at every level of industry, infrastructure, and structures.

Marshaling these resources to build the hydrogen economy will be challenging but not impossible. The challenges ahead are financial and political, not physical. America has more than enough resources to build and sustain the hydrogen economy. It lacks only the political will and national economic strategy to use those resources effectively. The Mission for America clean hydrogen plan provides a blueprint for the type of leadership and economic strategy needed to make developing a hydrogen economy of the necessary size a reality.