Upstaged by more climate-friendly fuels, hydrogen returns in a strong support role in the burgeoning renewables industry.
By Thomas K. Grose
Remember the Hydrogen Economy? Early in George W. Bush’s presidency, his administration viewed hydrogen as the clean fuel of the future and imagined mass production of fuel-cell-powered cars by 2020. Congress went along, approving hundreds of millions of dollars for research and development. Enthusiasts touted hydrogen as nonpolluting because, whether digested in a fuel cell or burned in an engine, it emits only water and heat, not carbon monoxide and other toxins. It also has, by weight, three times the energy content of gasoline. Oh—and it’s the most plentiful element in the universe.
So, yeah: an energy system based on hydrogen and electricity sounded pretty great—until it didn’t. Hydrogen may reduce smog, but it’s not altogether clean. Though ubiquitous, the element doesn’t exist on its own. Nearly all of it is derived from natural gas through a process called steam methane reforming, which releases carbon dioxide. An alternate method, splitting water to release hydrogen, requires electricity, and power generation in the early 2000s depended heavily on fossil fuels. Both production methods discharged greenhouse gases and contributed to global warming. In 2009, the climate-focused Obama administration pulled the plug on Bush’s Hydrogen Fuel Initiative.
End of story? Not quite. Today, hydrogen is staging a comeback, though not in a starring role. There’s no longer talk of a hydrogen economy. However, energy experts expect it to play an important supporting role in a future zero-carbon world. What saved it? A burgeoning renewables industry. Electricity from wind and solar is now the cheapest on the market, and production is quickly ramping up. And if the power to split water through electrolysis comes from renewables, the resulting “green hydrogen,” as it’s called, would be 100 percent clean and help to decarbonize the world.
The war in Ukraine, which heightened concern about western Europe’s dependence on Russian oil and gas, adds a new reason to find hydrogen attractive. Climate considerations aside, hydrogen expands the mix of reliable energy options and can be produced anywhere.
An ‘Old Thing’ Rediscovered
Reaching a zero-carbon future would first require ridding all electricity production of emissions, then electrifying everything that can be electrified, from passenger cars to heating. But that would get only partway to the goal. Some processes are hard or impossible to electrify, particularly heavy-weight, long-haul transport—including trucks, ships, and aircraft; steel manufacturing; and production of fertilizers and other chemicals. That’s where clean hydrogen could make a difference. The prevalent element and its derivatives—especially ammonia—are now seen as an ideal way to decarbonize those vehicles and industries. “Hydrogen is an old thing, but it is now being rediscovered,” explains Michael Timko, an associate professor of chemical engineering at the Worcester Polytechnic Institute. “And it will have a role to play.”
The Biden administration certainly thinks so. But officials also recognize that for hydrogen to fulfill its role, a more climate-friendly variety will be required than is currently available. Green hydrogen now accounts for only 1 percent of global production. So last August, the US Department of Energy launched its Hydrogen Shot, an initiative to accelerate breakthroughs in clean hydrogen production and use and to reduce the price of green hydrogen by 80 percent to $1 a kilogram (2.2 pounds). The administration spent $285 million on hydrogen research in the 2021 fiscal year and received $400 million in the current fiscal year. Additionally, the $1 trillion bipartisan infrastructure bill signed by the president in November 2021 authorized $9.5 billion for hydrogen research, of which $8 billion goes toward a network of regional hydrogen hubs to spur its industrial use. For the upcoming fiscal year, the White House is seeking $1.5 billion for hydrogen research.
Energy experts largely welcome DOE’s approach, but they are divided over various aspects. These include the department’s plan to make production of hydrogen from natural gas and other fossil fuels greener—but still not totally green—by combining it with carbon capture and sequestration (CCS). CCS traps most of the CO2 produced before it escapes into the atmosphere and then either buries it or turns it into a solid. Some experts object to DOE’s support for using electricity from nuclear plants to split water and to the department’s endorsement of using hydrogen to store excess energy from solar and wind farms. And there’s little enthusiasm for a plan to use hydrogen to heat buildings.
DOE’s drive to lower substantially the cost of green hydrogen and accelerate production draws wide support among experts. Doing this requires making electrolysis less expensive and building more electrolysis facilities, experts say. “Once it is done on scale, that will reduce costs. I am not worried about the costs coming down,” says Mark Jacobson, a professor of civil and environmental engineering at Stanford University. Robert Brecha, a professor of sustainability at the University of Dayton’s engineering school, agrees. As the price of renewable energy continues to fall, that will increase demand for electrolysis, he says. “It’s economies of scale and also learning how to do things better to increase capacity,” Brecha says. Improved electrolysis technology would extend the life of its components and make the process more efficient, he says.
A Super-Efficient Catalyst
Toward the cost-reduction goal, Zhenxing Feng, an associate professor of chemical, biological, and environmental engineering at Oregon State University, says his team has invented a new type of electrolyzer catalyst that is more efficient than today’s commercial versions by nearly three orders of magnitude. Paired with electricity from renewables, he says, the catalyst can produce hydrogen at a cost that meets the Hydrogen Shot’s target of $1 per kilogram. “Ours can be very competitive, even compared to natural gas reforming,” Feng says.
In electrolysis, electrochemical catalysts increase the rate of the chemical reaction. Feng’s team found that the reaction can cause irreversible structural changes, making the catalyst less stable. After studying this restructuring, the team manipulated the surface structure and composition of the catalyst. Instead of the common commercial catalyst based on iridium oxide, they found that a catalyst based on amorphous iridium dioxide actually becomes more efficient once it undergoes irreversible changes. Their catalyst is also cheaper. Fifty percent of the commercial catalyst is iridium oxide, “and iridium is ridiculously expensive,” Feng says. His catalyst uses only half of that amount of iridium, and he predicts future iterations will require even less, making them much cheaper. He has already patented the technology and licensed it to a manufacturer for commercial production.
The cost of green hydrogen could also be lowered with technologies other than electrolysis. One that has received a lot of attention is a photoelectrochemical process that uses solar power and specialized semiconductors to split water. “The main advantage is you skip the middle part” of using solar power to make electricity first, Timko says, which makes it a more efficient process. Photoelectrochemical is “among several in-the-lab technologies that really look promising; we are tracking their development,” says José Bermúdez, an energy technology analyst at the International Energy Agency in Paris.
A Low-Carbon Option or a Gimmick?
Enough varieties of hydrogen production methods are in the works that the community of hydrogen fuel scientists has taken to color-coding them: green, blue, gray, brown or black, turquoise, purple, pink, red, and white. The three main ones are gray, produced conventionally from natural gas with methane steam reforming; blue, produced using the same method as gray but paired with CCS; and green, produced from water using carbon-free electricity.
Industry considers blue hydrogen a low-carbon option. DOE agrees, but a paper published last August by Jacobson and Robert Howarth, a professor of ecology and environmental biology at Cornell University, shot a huge hole in that claim. The paper posits that the total greenhouse-gas footprint of blue hydrogen is so large that it would be better for the climate just to burn the natural gas. “Blue hydrogen is a nonstarter. It’s only a gimmick to keep the fossil fuel industry alive. You’ve got to look at the upstream emissions,” Jacobson says. Besides upstream leaks from the production and shipping of natural gas, the authors take into account the burning of natural gas to power CCS technology. Additionally, Jacobson and Howarth contend that CCS technology has a poor track record and is expensive. They also note that it remains unproven whether CO2 can be safely buried as part of sequestration.
But Jacobson and Howarth haven’t dealt blue hydrogen a fatal blow. “I have a problem with that paper,” says Jacob “Jack” Brouwer, a professor of mechanical and aerospace engineering at the University of California–Irvine and director of the National Fuel Cell Research Center. He’s one of around 20 authors who plan to publish a rebuttal. “We question some of their assumptions and analysis,” he says. Bermúdez sees a role for blue hydrogen if it meets three criteria: that the CCS has a high capture rate; that the captured carbon can be safely sequestered; and that upstream emissions are greatly reduced. “We have to make sure emissions are kept to a minimum or avoided,” Bermúdez says. However, that may prove hard to do, he adds.
And Brouwer admits that if it were cheap and easy to plug upstream emissions, it probably would have been done by now. He also concedes that CCS remains an unproven, expensive, and so far ineffective technology. Nevertheless, Brouwer says, when it comes to achieving the goal of limiting global warming to no more than 2ºC over preindustrial levels, every single model “says we need some CCS investment to reach that goal.” Brouwer calls himself “a fan of ridding ourselves of fossil fuels as fast as possible” but thinks it is acceptable to use blue carbon in the short term to reduce emissions. A recent article by an international team led by Christian Bauer, a researcher with the Paul Scherrer Institute in Switzerland, says that under certain conditions, blue hydrogen is compatible with low-carbon economies, but adds that “neither current blue nor green hydrogen production pathways render fully ‘net-zero’ hydrogen without additional CO2 removal.”
Also contentious is turquoise hydrogen. It comes from a process called methane pyrolysis, which uses extreme heat to split methane into hydrogen and solid carbon, or carbon black, a powder that is mainly used in tire manufacturing but can also be found in products ranging from inks to plastics. The DOE is giving Monolith, a Nebraska company, $1 billion in loan guarantees to fund the scaling up of a small “clean” pyrolysis plant to commercial size. Monolith says its capture technology aims to reduce emissions by up to 80 percent. Brecha says making turquoise hydrogen requires less electricity, uses all the natural gas, and produces a useful product. “That’s an interesting feature,” Brecha says, but if the goal is zero emissions, turquoise fails the test. “The best case is 70 percent to 80 percent capture, and in practice it’s a lot less than that.”
24/7 Nuclear?
Pink hydrogen is made using electricity from nuclear plants to split water. The DOE announced last May that its Idaho National Laboratory was starting a pilot project, the country’s first, to use power from one of its lab reactors to run an electrolyzer. During times when the grid has ample power, nuclear plants’ operations are tamped down. Ideally, in the future, the agency says, the plants could instead operate continuously at full tilt and use the extra electricity to produce hydrogen. But nuclear power is expensive, and, unlike solar and wind, it isn’t likely to get cheaper. Brecha has doubts: “It isn’t clear to me why we would go that route.”
If the world looks to rely heavily on low-carbon hydrogen, more needs to be done to expand the infrastructure for storing and transporting the gas, which is extremely flammable when it mixes with air or oxygen. “There is essentially zero hydrogen infrastructure in the US,” Brouwer complains. Currently, hydrogen is stored in tanks in highly compressed gas or liquid form. It can be transported by compressing it into long cylinders that are stacked on a so-called tube trailer and hauled by truck. Hydrogen can be liquified by chilling it to -253ºC and transported in super-insulated cryogenic tanker trucks, DOE says. Ships are being developed to transport hydrogen by sea in liquid form, chilled to at least -253ºC. Hydrogen pipelines are costly to build, which explains why there are just 1,600 miles of them in the United States, mainly on the Gulf Coast. Better technologies to store hydrogen and move it around are needed, Brouwer says, and would also help to reduce its cost. Many researchers are investigating solid and liquid chemicals that bond with hydrogen so it can be handled at low pressure and near-ambient temperatures.
The challenge of storing and transporting hydrogen is among the reasons ammonia is seen as key to the future of this low-carbon fuel. Ammonia doesn’t bond with hydrogen, but it’s a hydrogen derivative that’s much easier to store and transport. Additionally, ammonia’s energy density by volume is almost twice that of liquid hydrogen. Ammonia is currently produced using the century-old Haber-Bosch process, which combines hydrogen and nitrogen under high temperatures and pressure. Nearly all ammonia production now uses gray hydrogen, so the process emits huge amounts of CO2. If the Haber-Bosch process used green hydrogen instead of gray, the resulting ammonia would be green, too—except that when ammonia burns, it releases another greenhouse gas, nitrous oxide.
A Greener, Cheaper Haber-Bosch
Since 2013, a research farm operated by the University of Minnesota has been making green ammonia from electricity supplied by wind turbines while working to improve the process. Prodromos Daoutidis, a professor of chemical engineering and one of the farm’s researchers, says that green ammonia, like green hydrogen, is still expensive, but the prices of both will likely fall in tandem. “However, if we can improve Haber-Bosch it will also make a significant cost impact.” His team is one of many looking to revamp the catalysts used to make ammonia, so far with mixed results. But most of his work focuses on ways to reduce the amount of pressure and heat needed in the process. Specifically, Daoutidis is looking at absorbing the ammonia in salt under low pressure. This is much more energy-efficient than the current practice of relying on high-pressure condensation, followed by refrigeration, to extract ammonia. Daoutidis says researchers are also working on ways to improve the catalytic converters to capture nitrous oxide from burning ammonia.
Nitrogen fertilizers, which use ammonia as their key ingredient, represent an obvious potential market for green ammonia. “Agricultural use of green ammonia could be immediate,” Daoutidis says. “It’s a drop-in replacement.” Green ammonia is also seen as a potential carbon-free fuel for the marine industry. “Hydrogen on its own as a liquid or compressed takes up way too much payload,” Bermúdez says, “so ammonia can definitely play a role.” Shipping experts expect the industry eventually to embrace ammonia as a fuel, but the required overhaul of the global shipping fleet will be costly—around $2 trillion, by one estimate.
In a zero-carbon world, the intermittent nature of solar and wind power means that utilities must have sufficient storage to ensure round-the-clock electricity for customers. That’s where green hydrogen can play at least a backup role. Experts generally agree that batteries provide better short-term storage of energy than green hydrogen. Paul Martin, an expert in chemical processes and a member of the Hydrogen Science Coalition (HSC), explained to CNBC that if one joule of electricity is put in a battery, 90 percent of it is returned, but 67 percent of the electricity used to make and store hydrogen is lost. However, batteries aren’t capable of long-duration storage because they self-discharge over time. “If you need to store it for a long time, the equation changes. And if there are massive amounts to store, hydrogen would still be cheaper,” Brouwer says. “You can’t just think about short-term efficiency.” Other experts say ammonia is ultimately a better option than hydrogen because it’s easier to store and transport.
The DOE’s blueprint for increasing the use of hydrogen stresses its potential for use in combined power and heat systems in buildings, but experts are skeptical. “It’s not a great idea,” Bermúdez says. “Electric heating is five to six times more efficient.” He and others say electric heat pumps are a much better, more efficient remedy.
There is no debate, however, that clean hydrogen will be central to cleaning up many industrial processes that now emit enormous amounts of CO2—particularly steel manufacturing, the source of nearly 9 percent of carbon emissions, and production of iron, cement, and some chemicals. In steel production, for example, hydrogen is seen as a replacement for coke, a coal derivative, as a fuel and an agent for the reduction of iron oxides. “Hydrogen will play an important role in the decarbonizing of industry,” Bermúdez says.
Although the Bush administration’s big hydrogen initiative focused on passenger cars, no one expects hydrogen to power many light vehicles. Nearly all major automakers are pivoting to electric vehicles, and market forecasts predict that EVs will soon dominate new-car sales. However, the batteries that eat up space in electric cars aren’t a viable option for long-distance trucks and other heavy-duty vehicles that suck up massive amounts of energy. “Fuel cells can achieve the power required for heavy-duty trucks,” Bermúdez says. As for aviation, Brouwer says that smaller, short-range aircraft can be electrified. Both hydrogen and ammonia have been suggested as possible fuels for large commercial jets. Jacobson says his lab has run models showing that a slightly larger but lighter-weight version of the Boeing 747 could be powered by hydrogen fuel cells. However, given the long lead times needed to design new aircraft and certify their safety,“biofuels might be the first choice for aviation,” Brecha says.
If hydrogen can’t perform every part in a green-energy future, it’s certain to belong in the cast. Operating in conjunction with a growing supply of cheap, renewable electricity, hydrogen will thus defy the F. Scott Fitzgerald axiom, “There are no second acts in America.”
Thomas K. Grose is Prism’s chief correspondent.
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