The Hype and Hope for Hydrogen Part I

In June 2023, the Department of Energy published the U.S. National Clean Hydrogen Strategy and Roadmap to explore opportunities for “clean hydrogen” to decarbonize energy, transportation, and industry. The roadmap aims to develop a strategic framework to help achieve large-scale production and use of hydrogen from 2030 through 2050. 

 

The U.S. Department of Energy explores hydrogen uses in its U.S. National Clean Hydrogen Strategy and Roadmap. Image used courtesy of National Renewable Energy Laboratory.

 

Specifically, federal agencies plan to target hydrogen toward three segments of the economy: 

• Industrial applications: Chemicals, steelmaking, industrial heat 

• Transportation: Medium- and heavy-duty vehicles, maritime, aviation, rail 

• Power sector applications: Electricity generation, energy storage, stationary and backup power

Hydrogen has received a lot of press lately, but how does all of the hype match the real-world limitations of hydrogen as a viable decarbonization tool? In this two-part series, we will separate the hype from the hope.

Let’s start Part 1 with some hydrogen fundamentals.

 

Hydrogen: The Stuff of Stars

Hydrogen is the most abundant element in the universe. Made up of a single proton with a single orbital electron, it is the stuff that stars are made from. The nuclear fusion that occurs within a star results when hydrogen atoms in a plasma are smashed together, creating helium atoms and releasing nearly unfathomable amounts of energy. 

Another minor byproduct of star creation is small amounts of every other element on the periodic table, elements that are eventually used to create planets and all of the other matter that makes up the universe. We have briefly duplicated the atomic fusion that occurs in a star when we detonate a hydrogen atomic bomb.

 

H₂ on Earth

Here on Earth, if you combine two hydrogen atoms with an oxygen atom, you get water. If you combine four hydrogen atoms with a carbon atom, you get methane gas, which we also call natural gas. If you combine a ring of carbon atoms with a handful of hydrogen atoms, you can produce the oily hydrocarbons that make gasoline and diesel fuel. Combine chains of carbon with hydrogen, and the result is plastic. Put three hydrogen atoms together with nitrogen, and you get ammonia, which is the basis for fertilizer for agriculture.

Hydrogen can exist as H₂ gas, although it is somewhat unstable and readily combines with oxygen (think of the Hindenburg disaster). 

The most common ways to produce hydrogen gas are to use electricity to split water into hydrogen and oxygen (called electrolysis),  to use steam to separate it from carbon atoms in natural gas, or through a process called coal gasification. The last two methods are how more than 90 percent of commercially available hydrogen is made. 

Because of the energy required to spit hydrogen away from other atoms to produce pure gaseous hydrogen, it is usually thought of as an energy carrier rather than a source of energy.

 

Releasing Hydrogen’s Energy

Once you have hydrogen gas, you can retrieve the energy it carries either through combustion or by combining it with oxygen to produce water vapor. If you do this in an internal combustion engine (ICE), you can use the energy released to move the pistons up and down to move a vehicle. Hydrogen can also be externally combusted, and the jet of hot gas produced can be used to spin a turbine. 

Another way to retrieve the energy from hydrogen is to combine it with oxygen in a controlled manner in a fuel cell. By passing hydrogen and oxygen over a catalyst metal like platinum, the two can be combined to produce water vapor, at the same time releasing electrons that can be siphoned off and used to power an electric motor or other electric devices. Fuel cells have been used in spacecraft for decades to provide electric power beyond what can be produced by large solar panels. 

 

NASA’s Apollo spacecraft used hydrogen fuel cells to produce electric power. Image courtesy of NASA 

 

A Changing Climate

Because combining hydrogen with oxygen, either in an internal combustion engine (ICE) or a fuel cell, produces no hydrocarbon emissions, both methods are under consideration as ways to use hydrogen as a transportation fuel. 

Burning hydrocarbons like gasoline produces large amounts of carbon dioxide (CO₂), and over time, the tons of CO₂ emitted from vehicles, power plants, and industrial processes have accumulated in the upper atmosphere, creating a greenhouse effect that has begun to gradually warm the planet’s atmospheres and oceans. The warming has progressed, and it now has begun to change the weather, which has resulted in flooding, drought, more powerful storms, and record-high temperatures in Arctic regions and on the ocean surface. These changes are happening faster than the natural world can adapt, and large-scale extinctions of plants and animals are occurring, as well as famine, as drought prevents crops from growing.

To try to arrest the ravages of climate change, the use of fossil fuels like coal, oil, and natural gas is gradually being replaced with solar, wind, and nuclear energy to produce electricity for the power grid. The transportation sector has begun transitioning from gasoline and diesel fuels to electric vehicles (EVs) that use lithium-ion batteries to store the energy needed for electrified travel. 

Although EVs are becoming a practical alternative to gasoline-powered vehicles, they require that their batteries be charged more often than a gasoline tank needs to be filled, and recharging can take up to an hour at a DC fast-charging (DCFC) station—a delay that takes getting used to and that some motorists find unacceptable. Up until now, EVs are also more expensive than their ICE counterparts. 

Hydrogen might provide an alternative to battery-powered EVs as low or zero-emission fuel sources. In theory, this sounds simple. You can store hydrogen in onboard tanks on the vehicle and either replace gasoline with hydrogen in a conventional piston engine or pipe the H₂ gas into a fuel cell, producing electricity to power an electric motor and eliminating all of the batteries of a normal EV. It is the details, however, that let both of these strategies down. 

 

Making Hydrogen

More than 90 percent of commercial hydrogen comes from steam reforming of natural gas or through coal gasification. This produces what is called gray hydrogen because its production creates large amounts of CO₂ dumped into the atmosphere. Of all commercial hydrogen, 57 percent is used in oil refining. It is primarily used in a process that lowers the sulfur content of diesel fuel. In addition, 47 percent of commercial hydrogen is used to make ammonia, and about 70 percent of that is used to synthesize agricultural fertilizers. Hydrogen is also used to replace carbon dioxide in steelmaking, which is a growing market.

Because making gray hydrogen produces huge amounts of CO₂, there are plans to capture this greenhouse gas during the production process to create blue hydrogen. This sounds good, and vast amounts of resources are currently being spent to find ways to do it on large scales, but thus far, demonstration plants have shown limited success and require large amounts of energy to pull the CO₂ away from the hydrogen gas. For obvious reasons, oil companies that are already in the hydrogen production business are the biggest supporters of blue hydrogen.

Green hydrogen is the Holy Grail for hydrogen enthusiasts. Passing a direct current through water will break apart the hydrogen and oxygen bonds, producing gaseous H₂ and O₂. Ideally, the electrical energy used in this electrolysis comes from excess renewable energy such as wind or solar. Typically, the excess power is stored in a battery energy storage system (BESS). However, the green hydrogen that is produced can be stored and later used to power an electricity-producing gas turbine, or for any other use that gray hydrogen is currently used. 

Electrolyzers are about 67 percent efficient, and it takes about 50 megawatt-hours (MWh) of electricity to electrolyze one ton of hydrogen from water. Around 70 million metric tons of hydrogen are consumed annually, and to create all of that as green hydrogen through electrolysis would require more than 3.5 million gigawatt-hours (GWh) of electricity, and that’s a lot of energy. In 2022, the total amount of solar and wind electricity production combined was just under 700,000 GWh, so just supporting a green hydrogen economy would require a massive buildout of renewables. 

 

Transporting Hydrogen

Once you have made hydrogen, you need to move it to the location where it will be used. Currently, most hydrogen is transported in liquid form by tankers or as compressed gas by truck and trailer. Neither is efficient, and burning diesel fuel to transport hydrogen produces significant carbon emissions. 

 

Transporting hydrogen by truck. Image used courtesy of Wikimedia Commons (by Dicklyon)

 

Hydrogen can also be transported in pipelines, but hydrogen embrittles the welds in steel pipes, so the insides of the pipeline must be lined or coated to prevent this. High-pressure piping of this sort costs more than $1 million per mile. 

The best way to prevent the problems of transporting hydrogen is to make it where you plan on using it. 

 

Storing Hydrogen

Even if you don’t transport the hydrogen, you need to store it. Because hydrogen is such a tiny molecule, it can escape through most types of seals and gaskets. Hydrogen can be liquified by chilling it to near absolute zero and stored in cryogenic tanks. The technology is well established, having been used by NASA on the Apollo and Space Shuttle missions. Cooling the hydrogen takes a lot of energy—it takes about a third of the energy held in the hydrogen to turn it into a liquid. In addition, the storage tanks are large and bulky. 

The hydrogen also will eventually escape its cryogenic tank. In 2007 BMW demonstrated a hydrogen-powered automobile whose 10-gallon cryogenic liquid hydrogen storage tank kept its fuel at -253°C. After nine days of sitting, half of the full tank was observed to have evaporated away through the seals and piping system. 

Hydrogen can also be stored at very high pressures – up to 10,000 psi. High-pressure tanks for containing hydrogen are large and bulky and are usually made from high-strength composite materials, which makes them expensive. Compressing hydrogen to such a high degree also requires energy to run the compressors, and the heat created when the gas is compressed must be dealt with. As the pressure is reduced to make the hydrogen usable, it cools significantly and must typically be heated before it can be used. 

Hydrogen can also be stored in special compounds called metal hydrides that can store hydrogen by trapping them at ordinary temperatures and pressures and then releasing them as required. The downside is that the materials are heavy and are limited in their storage capacity, making the tanks large and heavy. 

Another way to store hydrogen is to convert it into liquid ammonia (NH₃) and then convert the ammonia back into hydrogen when it is needed. Transporting liquid ammonia is also much easier than transporting liquid or highly pressurized hydrogen. 

In addition to its use in oil refining, as a source of ammonia for fertilizer, and in steelmaking, hydrogen has several potential applications that take advantage of its zero-carbon emission possibilities. 

In Part 2, we will look at these new uses for hydrogen and separate the hype from the hope.