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Beyond electrolysis: do reservoirs of pure hydrogen exist?

Despite its easy logistics and flexibility (it can be used in fuel cells and adapted to combustion engines), hydrogen is expensive to produce and—experts say—is no viable alternative to fossil fuels. But would things change if hydrogen were found up for grabs in gaseous form and the reservoirs were big enough?

There are big hopes for a new type of energy exploration, this time in search of significant amounts of hydrogen in high purity percentages. If confirmed, the discovery could accelerate the adoption of hybrid engines combining hydrogen and electric cells, and thus solving the main obstacle to creating a zero-emission air-and-sea mass transportation.

But the reality today is rather grim: at the end of the last decade, the world barely consumed 70 million metric tons of hydrogen, all purposes combined, mainly to make ammonia for fertilizers and to refine crude oil (in comparison, global consumption of oil totaled 4.25 billion metric tons in 2021).

Despite its current insignificance, only hydrogen could compensate for the still low density of electric batteries in sectors like the aviation industry and sea logistics, among other uses.

Technological stagnation in the sky

The defense industry and several commercial companies are perfecting electric passenger aircraft capable of taking off and landing vertically as helicopters, as well as flying horizontally once at the desired cruise altitude. Known as eVTOLs, they could receive regulatory certification and soon carry the first passengers.

But eVTOLs, as these aircraft are known, battle with the laws of physics and an energy density constraint: it takes a lot of energy to fly gravity and basic aerodynamics to put big objects at altitudes high enough that the energy required for displacement becomes marginal (air density radically decreases the higher aircraft climb, making their movement dramatically more efficient, and allowing them to reach higher speeds).

Several teams have dedicated time and resources to solve this complex problem: how to efficiently put a plane high enough so it cruises for long distances without requiring huge amounts of energy-dense energy (like fossil fuel-derived jet fuel). In the rapidly evolving eVTOL market, as of today, the energy needs for taking off and landing are high enough to constrain the range of the rest of the flight.

This is why the first eVTOLs getting ready for regulation approval and commercial use (like the Toyota-backed company we recently visited in California, Joby Aviation, see video), are being marketed to investors and airline companies as a new type of “short-haul” commercial service, some sort of “flying taxis” capable of, for example, flying people from city center “skyports” to local airports avoiding traffic.

This use case is not yet enough for investors and companies who have dedicated resources studying the possibility of medium and long-range flights on electric aircraft: batteries aren’t dense enough yet to create, say, a bigger eVTOL capable of flying and landing vertically, while cruising vertically at speeds close to Mach 1, or even at supersonic speeds (several ongoing laboratory experiments test turbojet engines powered by liquid hydrogen).

Could eVTOLs be high-capacity and supersonic one day?

Consider, for example, the musings on long-haul, supersonic eVTOLs by Elon Musk (who has experience in experimental R+D on high-density batteries, vertical takeoff and landing—of space rockets no less—, autopilot neural networks, and advanced robotics).

The idea’s potential appeals to Musk as CEO of Tesla and SpaceX, but he also points out that some of the things that should happen before supersonic eVTOLs are feasible haven’t happened yet, and he has “enough on my plate,” mentioning Tesla’s efforts on mass-market cars and trucks, as well as SpaceX’s reusable rockets for commercial space applications (which, he clarifies, will continue to use fossil fuels due to the extraordinary energy density needed to put a heavy object in orbit).

“I guess, thinking about an electric plane is that you want to go as high as possible, but you need a certain energy density in the battery pack because you have to overcome gravitational potential energy. Once you’ve overcome gravitational potential energy, and you’re out at a high altitude, the energy use on cruise is very low. And then, you can recapture a large part of the gravitational potential energy on the way down. So, you really don’t need any kind of reserve fuel, if you will, because you have the energy of height, gravitational potential energy. This is a lot of energy.”

“So, once you can get high, like the way to think about a plane is it’s a force balance. So, the force balance… So, a plane that is not accelerating is a neutral force balance. You have the force of gravity, you have the lift force, you have the wings. Then, you’ve got the force of the whatever thrusting device, so the propeller, or turbine, or whatever it is. And you’ve got the resistance force of the air.

“Now, the higher you go, the lower the air resistance is. Air density drops exponentially, but drag increases with the square, and exponential beats the square. The higher you go, the faster you will go for the same amount of energy. And at a certain altitude, you can go supersonic with less energy per mile, quite a lot less energy per mile than an aircraft at 35,000 feet because it’s just a force balance.”

Air travel’s dependence on jet fuel

To Musk, solar energy and stationary energy associated with renewable energy production have a bigger priority for their potential positive impact and a potentially bigger impact on the climate at a big scale than supersonic eVTOLs. But, would this priority list hold if new designs for electric airplanes could replace in the medium term the majority of commercial airplanes (as produced by Airbus, Boeing, and their competitors in smaller commercial aircraft, such as Embraer and the future eVTOLs getting ready to market as “flying taxis”?).

Are commercial electric aircraft even possible with today’s technology? The biggest remaining hurdle seems to be the amount of energy needed to fly the aircraft to cruise mode at high altitudes, which would require a gravitational energy density not capable with today’s conventional batteries.

Gravitational energy is the potential energy required by a massive object to distance itself from another massive object (in this case, Earth) and thus fight the gravitational field; as founder and CEO of SpaceX, Musk understands that the same gravitational field complicating things during takeoff becomes an advantage when the same massive object approaches Earth again (that is, descends): the field is “released” then, or transformed in kinetic energy that could be gathered with some sort of fast charging technology transforming heat into electricity.

But big aircraft with electric engines aren’t doomed to wait for decades in the hope of electric batteries dense and light enough to be able to compete with the extremely caloric (and hence capable of releasing a vast amount of energy per unit of weight) fossil fuel options of today.

Like in cars, electric engines in planes would dramatically simplify current combustion engines, as well as decrease their weight and finish with technical constraints that prevented designers from locating several engines in different parts of a big aircraft. Today, as Joby Aviation engineers explained to us a few weeks ago, electric engines are so small, light, and efficient that they could go anywhere in an aircraft; one would only need to run an energy cable from their location to the energy source.

Hydrogen and electric power trains in “transition” aircraft

Unlike purely electric engine power trains relying on heavy batteries, a hybrid approach combining hydrogen and electric power trains could use a zero-emissions liquid fuel for the energy-demanding task of taking off and gaining altitude fast, whereas electric power could propel the flight once in cruise mode. Hydrogen can be stored as a liquid fuel, and, when burned, it only produces water. Liquified hydrogen is several times more energy-dense than the densest batteries and at a fraction of the batteries’ total weight.

There’s plenty of hydrogen around, though there’s a caveat that hasn’t been solved: there’s virtually no pure hydrogen on our planet, and it currently takes a lot of energy to produce it. There’s a big caveat that nurtures skeptics of a sustainable flying industry in the medium term: would it make sense to use large amounts of the current energy mix (still heavily reliant on fossil fuels) to produce liquified hydrogen? So far, no big investment has created big production facilities capable of mass-producing hydrogen with renewables.

Experimental processes promise to extract clean fuel from water by splitting oxygen and hydrogen using just sunlight on top of silicon devices that store the two components separately. In producing hydrogen with renewables, the only waste product derived from such a process would be water, hence its appeal and potential. The process used to extract hydrogen from water is electrolysis.

Like traditional car manufacturers, big aircraft manufacturers have explored the idea of using hydrogen because the current engine designs could be easily repurposed during a transition period. But, is this ability to potentially use liquid hydrogen on modified aircraft power engines an advantage or a deterrent preventing the industry from evolving at a faster path?

The evolution of hydrogen as an alternative in the car industry is a cautionary tale: big car manufacturers have produced car prototypes that use hydrogen fuel cells for decades, yet the technology keeps being a part of the future. While mass-produced hydrogen vehicles are still “years away,” aircrafts’ engines have become more efficient but essentially keep a decades-old engine design.

A hydrogen-electric 19-seater

The largest passenger plane tested yet with a hydrogen-electric engine is a two-propeller, 19-passenger aircraft adapted by the British-American startup ZeroAvia.

The company promises safety, zero emissions and reduced noise for medium-range flights, and a similar flying experience to small planes with combustion-powered propellers. The 19-seater hydrogen-electric plane completed a 10-minute (!) test flight by mid-January 2023 in Cotswold Airport (Gloucestershire, UK) and hopes to make bigger models (up to 90 passengers) to create a “hydrogen-powered” market for commercial flights.

Once the test campaign is completed, planes with 2-cell and lithium-ion batteries for peak power could apply for certification and cover routes of a few hundred kilometers on 10 to 20-seat configurations, using aircraft designs such as the adapted twin-engine turboprop Dornier 229 (a 10-seater from Germany), the Otto Celera 500L by the US startup Otto Aviation, a light prototype with up to 6 passengers, and the 11-seater Grand Caravan by the also American small plane manufacturer Cessna.

Such hydrogen test flights use legacy technology with adapted combustion propellers to work with hydrogen fuel cells, and the aircraft are also limited in range, speed, and versatility. Two-propeller airplanes such as the German Dornier 228 are eSTOL aircraft or electric “short takeoff and landing” planes, yet they aren’t eVTOLs (electric “vertical” takeoff and landing aircraft like the gigantic-drone looking Joby) and very far from something supersonic (the conventional Dornier 228 has a cruise speed of 413 km/h (or about 257 mph).

To overcome the resistance force of the air, which decreases as it gets thinner at higher altitudes, planes can fly fast and efficiently, especially those equipped with turbine engines instead of the (more efficient) airplanes with propellers. Hydrogen, hydrogen-electric, or purely electric passenger airplanes capable of taking off and landing vertically, as well as carrying a heavy load of passengers and cargo, are today only a matter of speculation.

Elon Musk says he has “a lot on my plate”:

“The airplane, electric airplane isn’t necessarily right now. Electric cars are important.

“Solar energy is important. Stationary storage of energy is important. These things are much more important than creating electric supersonic futile. Also, the plane’s naturally — You really want that gravitational energy density for an aircraft, and this improving over time. So, you know, it’s important that we accelerate the transition to sustainable energy. That’s why electric cars; it matters whether electric cars happen sooner or later. You know, we’re really playing a crazy game here with the atmosphere or the oceans.”

A “gold mine” of clean energy nobody sees?

Would things change for long-haul flights at high speeds if we knew how to tap into the abundant source of hydrogen blended with other molecules around us? British turbine manufacturer Rolls-Royce announced on November 2022 that it had successfully tested a turbine aircraft engine on hydrogen, “a world aviation first.”

Like European aircraft manufacturer Airbus and its main rival, Seattle-based Boeing, Rolls-Royce has also been studying electric engines, which are only suitable for short flights due to the lower energy density of batteries vs. stored jet fuel (or hydrogen).

But, as it happened with combustion engines in the automobile industry until Tesla represented a sizable commercial threat to the end of the industry, the aircraft industry doesn’t seem to be rushing to find alternatives to conventional engines, which have become more efficient but rely on a technology that hasn’t changed dramatically in the last decades. Airbus acknowledged recently that most commercial airliners will use gas turbines until at least 2050. Would these predictions change if a new company demonstrated that hydrogen-electric airliners are viable and secure in middle and long distances?

If hydrogen engines could ease the transition on long-haul trips for the aviation industry, nobody seems to be rushing to effectively substitute jet fuel from the aerial mass travel equation.

This could only change if there were a breakthrough in the ways we produce hydrogen on a big scale. In this respect, business and economics columnist Peter Coy wonders in one in one op-ed article for the New York Times whether we are sitting in “a gold mine of clean energy” related to hydrogen production, and the key could be “hiding under our feet.”

Quoting Daniel Kahneman, Peter Coy acknowledges that our civilization has shown moments in which solutions to existential problems lay in front of us, but our perception (perhaps too attached to custom and narcotized by the comfort of the self-propelling inertia of post-modernity) fights against potentially transformative innovations:

“You know what else has been hiding in plain sight? Hydrogen, the most abundant element in the universe. Hydrogen, which is heralded as the clean energy carrier of the future because its only combustion product is water.”

The immense potential of hydrogen prospection

Locked in oxygen within the water or mixed with carbon in fossil fuels like propane, it can be expensive (and polluting) to get lots of hydrogen at a big scale. Despite not existing freely in nature, there are potential ways to produce it that wouldn’t require using methane (and therefore releasing the carbon dioxide that the use of hydrogen would try to prevent in the first place): if hydrogen from water requires lots of electricity, how about “drilling for it” the way we drill for fossil fuels. Peter Coy:

“Just think how much cheaper and easier it would be if we could drill for hydrogen the same way we drill for oil and natural gas, and thus put to good use society’s enormous investment in equipment built for the exploration, production, and transportation of fossil fuels.”

Only a handful of scientists have been paying attention until now to “natural hydrogen,” which, according to an article produced in Science, it’s hidden under the Earth’s crust, waiting to be reached —and potentially used at the scale of crude oil.

The Science article starts with a fortuitous discovery near the town of Bourakébougou, in Mali. Diggers had come digging for water in the late eighties, but they were surprised by the explosion of gas after a worker peered into the hole smoking a cigarette. In 2012, a study of the gas determined that it was “98% hydrogen“:

“Within a few months, Brière’s team had installed a Ford engine tuned to burn hydrogen. Its exhaust was water. The engine was hooked up to a 30-kilowatt generator that gave Bourakébougou its first electrical benefits: freezers to make ice, lights for evening prayers at the mosque, and a flat-screen TV so the village chief could watch soccer games. Children’s test scores also improved. “They had the lighting to learn their lessons before going to class in the morning,” Diallo says. He soon gave up on oil, changed the name of his company to Hydroma, and began drilling new wells to ascertain the size of the underground supply.

“The Malian discovery was vivid evidence for what a small group of scientists, studying hints from seeps, mines, and abandoned wells, had been saying for years: Contrary to conventional wisdom, large stores of natural hydrogen may exist all over the world, like oil and gas—but not in the same places. These researchers say water-rock reactions deep within the Earth continuously generate hydrogen, which percolates up through the crust and sometimes accumulates in underground traps. There might be enough natural hydrogen to meet burgeoning global demand for thousands of years, according to a US Geological Survey (USGS) model that was presented in October 2022 at a meeting of the Geological Society of America.”

Hidden Hydrogen: Does Earth hold vast stores of a renewable, carbon-free fuel? February 16, 2023, Erich Hand

Pure hydrogen up for discovery

According to Peter Coy, the optimism is welling up: what if hundreds of millions of megatons of hydrogen are waiting to be used once drilled from Earth’s crust? At the current consumption rates, “that would last thousands of years.” Transportation and machinery could use fuel cells at an even bigger scale than today’s massive combustion engines, used in automotive and aircraft industries and in the biggest diesel-powered vessels ever constructed.

The byproduct of such engines would yield an exhaust of… reusable water. Too good to be true? Why hasn’t the fossil fuel industry even tried to invest so far in the potential of drilling pure hydrogen? As of today, hydrogen is “mainly used for lightening and sweetening crude oil, making ammonia for fertilizer, treating metals, and processing foods.” But why not use it to generate electricity or power vehicles?

Natural hydrogen from the ground could be produced, according to experts, for less than $1 per kilogram, much cheaper than the current $5 per kilogram derived from water through electrolysis. Why is nobody using pure hydrogen at a big scale if the current hyper-sophisticated drilling industry could be easily adapted to the new task?

According to the people interviewed by Science and Peter Coy, we just didn’t know much about it: scientists thought that the pockets of pure hydrogen found in fortuitous ways were “anomalies.” Scientists had guessed that any hydrogen in a pure state in the crust wouldn’t survive as an independent molecule, eaten by microbes or leaking to the surface and into space, like the methane trapped in a frozen state beneath the Siberian tundra is doing as the surface melts in the increasingly hot summer months.

Are legacy companies up to the task?

Since the discovery in Mali in 2012, reservoirs of hydrogen gas have a clear precedent:

“Geologists now believe that hydrogen is being constantly produced from a reaction between water and iron-rich rocks. It’s essentially rusting: The rocks capture the oxygen and release hydrogen. Some hydrogen may also be bubbling up from deeper in Earth or be formed by radioactivity, which splits water molecules. Hydrogen has been found on all the continents except Antarctica, which hasn’t been checked yet.”

Until now, few companies thought it was a good idea to use large amounts of electricity to produce liquified hydrogen, then transport it, and finally extract the energy through its use on an adapted combustion engine or a fuel cell. Now, it all changes “if hydrogen is available in gaseous form in the ground.” The economics would all of a sudden make sense, says Isabelle Moretti, the leading scientist of the French energy company Engie.

We may be in the early days of a new energy opportunity, this time one that would produce reusable water as waste and could help big aircraft (including future supersonic models) abandon fossil fuels.