Bronte Wells
Hydrogen is a versatile energy carrier that can be used to store, move, and deliver energy produced from other sources. It is often touted as a low-carbon replacement for fossil fuels in various applications, including transportation, electricity generation, and heavy industry. While hydrogen is a clean fuel that produces only water when consumed in a fuel cell, the methods used to produce it can impact its environmental footprint. Currently, most hydrogen is produced from fossil fuels, contributing to significant CO2 emissions. However, low-emissions hydrogen produced with renewable or nuclear energy offers a promising path toward decarbonization in sectors where emissions are challenging to abate. As hydrogen demand increases, the question of whether it is a pollution-free fuel becomes more critical, with safety, cost, and infrastructure considerations also playing a role in its potential as a future clean energy solution.
| Characteristics | Values |
|---|---|
| Hydrogen as a fuel | Hydrogen is a versatile energy carrier that can be used in cars, houses, and for portable power. |
| Hydrogen production | Hydrogen can be produced from various sources, including natural gas, coal, solar energy, wind, biomass, nuclear power, and renewable liquid fuels. The most common methods of production are natural gas reforming and electrolysis. |
| Environmental impact | Hydrogen is promoted as a "carbon-free" fuel when produced from renewable energy sources. However, currently, only 1% of hydrogen is generated renewably, with 99% derived from fossil fuels, primarily methane. The burning of hydrogen produces nitrogen dioxide, a respiratory irritant and air pollutant. |
| Cost | The cost of hydrogen production varies depending on the method, with green hydrogen costing between $2.50/kilogram and $4.50/kilogram. The cost of fuel cells needs to decrease to be competitive in the marketplace. |
| Applications | Hydrogen has potential applications in the transportation sector, where it can power fuel cell electric vehicles or hydrogen internal combustion engine vehicles. It can also be used for electricity generation and energy storage. |
| Challenges | Hydrogen has low energy content by volume, making storage challenging due to the high pressures and low temperatures required. There are also safety concerns associated with the explosive potential of hydrogen. |
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What You'll Learn
Hydrogen as a clean fuel
Hydrogen is a versatile energy carrier that can be used to store, move, and deliver energy produced from other sources. It is considered a clean fuel that, when consumed in a fuel cell, produces only water vapour. However, when hydrogen is combusted, it produces nitrogen oxide (NOx), a harmful pollutant and respiratory irritant.
Hydrogen can be produced from various domestic resources, such as natural gas, nuclear power, biomass, and renewable power like solar and wind energy. The most common methods of production today are natural gas reforming (a thermal process) and electrolysis, but other methods include solar-driven and biological processes. For example, biological processes use microbes such as bacteria and microalgae to produce hydrogen through biological reactions.
The use of hydrogen as a fuel has been proposed as a low-carbon replacement for fossil fuels in various applications, such as powering vehicles, heavy industry, and heating buildings. However, critics argue that many hydrogen projects will only serve to prolong the use of fossil fuels and require additional investments in fossil fuel infrastructure.
To be a truly clean fuel, hydrogen must be produced using renewable or nuclear energy, or fossil fuels with carbon capture, to help decarbonise sectors such as heavy industry and long-distance transport. This type of hydrogen, often referred to as "green hydrogen," has the potential to reduce emissions in sectors where alternative solutions are unavailable or difficult to implement. However, as of 2023, low-emissions hydrogen production accounts for less than 1 Mt of the total 97 Mt global hydrogen demand.
While hydrogen has the potential to be a pollution-free fuel, challenges remain in terms of production methods, infrastructure, and cost. To realise the benefits of hydrogen as a clean fuel, faster action is needed to create demand for low-emissions hydrogen and bring down production costs.
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Hydrogen fuel production methods
Hydrogen is a clean fuel that, when consumed in a fuel cell, produces only water vapour. Hydrogen can be produced from a variety of domestic resources, such as natural gas, coal, nuclear power, biomass, and renewable power like solar and wind.
Today, hydrogen fuel is mainly produced from fossil fuels, in particular, natural gas, which are non-renewable sources. Hydrogen is produced through a variety of methods, with the most common being natural gas reforming and electrolysis.
Natural Gas Reforming
Natural gas reforming is a thermal process that involves steam reforming, a high-temperature process in which steam reacts with a hydrocarbon fuel to produce hydrogen. This process is also known as steam-methane reforming, where hydrogen is produced from a chemical reaction between steam and methane, the main component of natural gas. This process emits a significant amount of carbon dioxide and a small amount of carbon monoxide. When carbon capture and storage are used to remove emissions, the product is called blue hydrogen.
Electrolysis
Electrolysis is a process that uses electricity to split water into hydrogen and oxygen. Electrolysis can be powered by renewable energy sources, and the hydrogen produced from this method is called green hydrogen. Electrolysis can also be combined with other processes, such as carbon/hydrocarbon assisted water electrolysis (CAWE), to reduce the energy intensity and cost of hydrogen production.
Solar-Driven Processes
Solar-driven processes use sunlight as the agent for hydrogen production. These processes include photobiological, photoelectrochemical, and solar thermochemical methods. Photobiological processes use the natural photosynthetic activity of bacteria and green algae to produce hydrogen, while photoelectrochemical processes use specialized semiconductors to separate water into hydrogen and oxygen. Solar thermochemical hydrogen production uses concentrated solar power to drive water-splitting reactions.
Biological Processes
Biological processes use microbes such as bacteria and microalgae to produce hydrogen through biological reactions. In microbial biomass conversion, microbes break down organic matter like biomass or wastewater to produce hydrogen, while utilizing sunlight as an energy source.
Other Methods
Other hydrogen production methods are currently being explored, such as the partial oxidation reaction, which involves the partial combustion of a fuel-air mixture or fuel-oxygen in a reformer or partial oxidation reactor. Additionally, hydrogen can be produced from biofuels, petroleum fuels, and through nuclear power.
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Hydrogen fuel transportation
Hydrogen is a clean fuel that offers an attractive alternative to fossil fuels for transportation and electricity generation applications. Hydrogen can be used in cars, houses, and for portable power.
The transportation sector accounts for approximately 30% of total US energy needs and 70% of US petroleum consumption. Hydrogen can be produced domestically from resources like natural gas, coal, solar energy, wind, and biomass. Hydrogen can be used to power highly efficient fuel cell electric vehicles (FCEVs) or hydrogen internal combustion engine vehicles (HICEVs). FCEVs are electric vehicles that use an electric motor instead of an internal combustion engine to power the wheels. They produce electricity onboard and emit only water and heat as byproducts. HICEVs, on the other hand, use hydrogen as a low-emission fuel in internal combustion engines.
FCEVs and HICEVs offer several benefits over traditional internal combustion engine vehicles. They produce little to no tailpipe emissions, significantly reducing greenhouse gas emissions. They also have a longer range than battery-electric vehicles, making them suitable for long-haul trucks, locomotives, and ships. Additionally, FCEVs and HICEVs can refuel quickly and extend the range of the vehicle over battery-powered vehicles.
However, there are some challenges associated with hydrogen fuel transportation. Hydrogen has a low volumetric energy density, which means it requires high pressures, low temperatures, or chemical processes for compact storage. This can be a challenge for light-duty vehicles with limited size and weight capacity for fuel storage. The cost of fuel cells is also high, and the infrastructure for hydrogen transportation, including pipelines, liquefaction plants, trucks, and storage facilities, is still being developed and expanded.
Despite these challenges, hydrogen has the potential to play a significant role in the transportation sector, especially for heavy-duty vehicles and long-haul applications. With advancements in technology and infrastructure, hydrogen fuel transportation can become more efficient and cost-effective, contributing to a more sustainable and resilient energy system.
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Hydrogen fuel storage
Hydrogen is a clean fuel that can be used in cars, houses, and for portable power. It has the highest energy per mass of any fuel. However, its low ambient temperature density results in low energy per unit volume. This requires the development of advanced storage methods with higher energy density. Hydrogen can be stored physically as either a gas or a liquid.
Storing Hydrogen as a Gas
When stored as a gas, hydrogen typically requires high-pressure tanks (350-700 bar, which is 5,000-10,000 psi tank pressure). The required large storage volumes may have less impact on larger vehicles, but providing sufficient hydrogen storage across all light-duty platforms remains a challenge. The storage capacity for hydrogen in light-duty vehicles should enable a driving range of more than 300 miles to meet consumer needs.
Storing Hydrogen as a Liquid
Storing hydrogen as a liquid requires cryogenic temperatures because the boiling point of hydrogen at one atmosphere pressure is -252.8°C. Hydrogen has to be cooled to -253°C and stored in insulated tanks to maintain this low temperature and minimize evaporation. This requires a complex plant. Complexity and cost have limited the use of liquified hydrogen to date.
Ammonia as a Storage Alternative
Ammonia (NH3) releases H2 in an appropriate catalytic reformer. Ammonia provides high hydrogen storage densities as a liquid with mild pressurization and cryogenic constraints. It can also be stored as a liquid at room temperature and pressure when mixed with water. Since there is no carbon in ammonia, no carbon by-products are produced, making it a "carbon-neutral" option for the future. However, ammonia is a toxic gas with a potent odour at standard temperature and pressure.
Other Storage Methods
Other methods of storing hydrogen include lightweight hydrides, which offer high gravimetric hydrogen storage but require high temperatures for desorption. Some are easy-to-fuel liquids at ambient temperature and pressure, while others are solids that could be turned into pellets. Gas storage in salt caverns is another established method, as well as depleted oil fields and aquifers.
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Hydrogen fuel emissions
Hydrogen is a versatile energy carrier that can be used to store, move, and deliver energy. It is considered a clean fuel that, when burned, does not produce carbon dioxide (CO2) or other greenhouse gases, only water vapour. This means that burning hydrogen does not contribute to climate change.
However, hydrogen production can have a significant environmental impact, depending on how it is produced. Currently, most hydrogen is produced using fossil fuels, such as coal and natural gas, which are responsible for substantial CO2 emissions. Steam reforming, a process that reacts high-temperature steam with natural gas to extract hydrogen, is the most common method of hydrogen production in the United States. Other methods include electrolysis, using electricity or sunlight to split water into hydrogen and oxygen, and thermochemical processes that "reform" natural gas or coal or "gasify" biomass.
Low-emissions hydrogen, produced with renewable or nuclear energy, or fossil fuels with carbon capture, can help to decarbonize sectors where emissions are hard to abate, such as heavy industry and long-distance transport. While the demand for low-emissions hydrogen is growing, it currently plays a marginal role, with regulatory uncertainties, cost pressures, and lack of infrastructure inhibiting faster adoption.
In terms of emissions, hydrogen fuel cell vehicles (FCEVs) are considered zero-emission, emitting only water vapour and warm air as exhaust. However, hydrogen internal combustion engines produce tailpipe emissions and are less efficient. Additionally, proposals to combust hydrogen to produce electricity have raised concerns about increasing nitrogen oxide (NOx) emissions, a harmful pollutant.
Overall, while hydrogen has the potential to be a pollution-free fuel, the current production methods often involve fossil fuels, which contribute to CO2 emissions. The transition to low-emissions hydrogen production and the development of hydrogen fuel cell technology are crucial for harnessing the benefits of hydrogen as a clean energy alternative.
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Frequently asked questions
Hydrogen is a clean fuel that, when consumed in a fuel cell, produces only water vapour. However, when hydrogen is burned, it produces nitrogen oxide (NOx), a harmful pollutant and respiratory irritant.
Hydrogen is a versatile energy carrier that can be used to store, move, and deliver energy produced from other sources. Hydrogen can be produced from domestic resources like natural gas, coal, solar energy, wind, and biomass.
Hydrogen is currently produced mostly from fossil fuels, which contributes to significant annual CO2 emissions. Hydrogen also has low energy content by volume, making it challenging to store due to the high pressures, low temperatures, or chemical processes required.
Hydrogen can be produced through various methods, including natural gas reforming, electrolysis, solar-driven processes, and biological processes using microbes such as bacteria and microalgae.
The production and burning of hydrogen from fossil fuels can lead to carbon dioxide, methane, and nitrogen dioxide emissions, which are harmful pollutants and respiratory irritants. These emissions disproportionately impact vulnerable communities, particularly communities of colour, and can exacerbate respiratory health issues such as asthma and COPD.
