Green hydrogen has many possible applications
Bernat Armang/The Associated Press/Alamy
Hydrogen, the most abundant element, releases energy when combined with oxygen, and the only byproduct is water. That's why politicians are touting it as a “Swiss Army knife” in the fight against climate change, capable of powering vast numbers of vehicles and industrial processes that currently run on fossil fuels.
Today, however, 99 percent of the hydrogen supply is “gray” hydrogen produced by splitting methane or coal gas, a process that releases carbon dioxide. To achieve net-zero emissions, many countries plan to rely instead on “blue” hydrogen, where this CO2 will be captured in a stack and injected underground, or “green” hydrogen, which is produced by sharing water with renewable electricity.
Green hydrogen is an “important bet Western countries must make” to compete with China on clean technology, UN chief Antonio Guterres said This was announced at a conference on December 3.
The problem is that low-carbon hydrogen is at least twice as expensive as gray hydrogen. Increasing production in order to reduce its cost will require government subsidies. While countries like the European Union support the industry, President Donald Trump has begun canceling planned low-carbon hydrogen hubs. as part of a $7 billion program in the United States.
Because of these obstacles, research firm BloombergNEF halved its forecast for low-carbon hydrogen production to 5.5 million tons by 2030, roughly 5 percent of current gray hydrogen consumption. With supplies limited, experts say governments and companies should focus only on the uses of clean hydrogen that make the most sense for the climate and the economy.
“Hydrogen can do almost anything, but that doesn’t mean it should,” says Russell McKenna at ETH Zurich in Switzerland.
In a recent studyMcKenna and his colleagues analyzed the CO2 emissions that would have to be released to produce and transport low-carbon hydrogen in 2,000 planned projects around the world, comparing them with the CO2 emissions that hydrogen could displace. They found that hydrogen could have the greatest positive climate impact in the steel, biofuel and ammonia industries.
On the other hand, using hydrogen for road transport, electricity generation and home heating will not lead to such significant reductions in emissions.
Steel
In a blast furnace, coke produced from coal not only provides heat to melt iron oxide, but also carbon for the reaction that removes oxygen from that ore. Therefore, it is not enough to simply heat metal with renewable electricity. You need something that replaces the carbon in a reaction that hydrogen can do, releasing water rather than CO2.
“The technology we have today that will allow iron to be produced on a full industrial scale from iron ore without producing CO2 is hydrogen technology,” says David Dye at Imperial College London. “Everything else requires you to invent a lot of future technologies.”
Stegra, A. green steel The startup is building a plant in northern Sweden that plans to produce steel using an electric arc furnace and green hydrogen produced from river water by the end of 2026, becoming the first carbon-free steel plant. There are also projects in other countries in Europe, Asia and North America.
But producing green hydrogen and powering arc furnaces requires cheap, renewable electricity. ArcelorMittal, the multinational steel corporation, this year scrapped a €1.3 billion subsidy to convert two steel plants in Germany to hydrogen as it said electricity prices were too high.
Ammonia
Plants require nitrogen in the form of nitrates to grow, but the soil holds them in limited quantities. However, in the early 20th century, chemists Fritz Haber and Carl Bosch developed a process for reacting nitrogen, which is abundant in the air, with hydrogen to form ammonia, which can be converted into various fertilizers.
This led to a revolution in agriculture and a surge in population worldwide, and hydrogen today is primarily used to produce ammonia as well as oil refining. About 70 percent of all ammonia goes into fertilizer, and the rest goes into the production of plastics, explosives and other chemicals.
“We can't electrify it… because it's a chemical reaction that requires that input,” McKenna says. “So we need hydrogen, but it has to be decarbonized hydrogen.”
Countries such as Saudi Arabia have begun building plants to produce hundreds of thousands of tons of green ammonia using solar and wind power, mostly for export. Meanwhile, startups are developing small, modular plants to produce green hydrogen and ammonia on farms in the United States. But at the moment, all these approaches are based on public investment or tax incentives.
Alternative fuels
Ammonia can also be burned in the engine. While cars and many trucks can run efficiently on electricity, long-distance vehicles such as heavy trucks, ships and airplanes can have difficulty transporting and charging batteries. Hydrogen is likely to be critical to producing low-carbon fuels for this sector.
McKenna and his team's research found that producing hydrotreated vegetable oil is one of the most efficient uses of hydrogen. This involves treating used vegetable oil with hydrogen to break down fats into hydrocarbons that can be burned.
Both ammonia and hydrotreated vegetable oil are considered as substitutes for heavy fuel oil in shipping, which accounts for 3 percent of global emissions. Aviation, with its similar carbon footprint, could also switch to ammonia.
But hydrogen can also be used to produce synthetic aviation fuel, which can be used in any aircraft today because it is almost identical to kerosene, only produced without the use of oil.
In the long term, researchers at institutions such as Cranfield University in the UK are developing aircraft with heavy-duty compressed hydrogen storage tanks. Although hydrogen or ammonia releases nitrogen oxides when burned, they can instead combine with oxygen in a fuel cell to produce electricity and water. Fuel cell aircraft are the ultimate goal, says Phil Longhurst at Cranfield University.
“Hydrogen is the cleanest, most carbon-free fuel we can get,” he says, “so it’s kind of the Holy Grail.”
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