Your definitive guide to understanding hydrogen

Senior Science and Economics Correspondent
Illustration. A hand holds a hydrogen production plant surrounded by questionmarks drawn in marker on a peach background.
Illustration by Nadya Nickels.

The cleantech space is positively buzzing about hydrogen. 

Before hydrogen burst on the climate scene in recent years, you might not have heard much about it since high school chemistry class. 

So, what is hydrogen and why is everybody talking about it now? 

Consider this your hydrogen cheat sheet. 

Hydrogen is the simplest, most abundant element in the universe. It’s a colorless and odorless gas. Stars, including our sun, are fiery balls of hydrogen. Hydrogen is very light — so light Earth’s gravitational field cannot hold it and individual molecules float away into space. 

There are, however, atoms of hydrogen on Earth contained in other liquids, gases and solids. Hydrogen smushed together with oxygen makes water. Hydrogen smushed together with carbon makes hydrocarbons, like natural gas, coal and oil. Reservoirs of hydrogen gas also lurk under Earth’s surface, trapped in pores of rocks underground. 

Hydrogen is already a big business unrelated to cleantech. Estimates for the current size of the global hydrogen market range from $163 billion to $207 billion 

The world produces and uses about 95 million metric tons of hydrogen a year, according to a 2023 International Energy Agency report, devoting more than 43% of that to refining petroleum.

Almost all of the remaining hydrogen is used in industrial processes to make a range of things our society depends on, including iron, steel and ammonia, a key component in fertilizer. 

Here’s a wild stat that underscores how essential hydrogen already is to our way of life: Without the fertilizers made with hydrogen, there would only be enough food to support just over half the global population.  

Hydrogen is valuable in making things because it’s both light weight and has a high energy content. As a gas, hydrogen takes up a lot of space, so it’s often compressed or converted to a liquid form. For example, NASA uses liquified hydrogen as rocket fuel. By weight, the energy content of hydrogen is about three times more than that of gasoline.  

What’s more, burning hydrogen generates water and heat — but does not produce greenhouse gas emissions. A lot of the energy in hydrogen gets lost as heat when it is burned, so a more efficient way to get the chemical energy out of hydrogen is in a fuel cell, a device that converts hydrogen into electricity with water as the only byproduct.  

Because of these traits — its energy density, its light weight and lack of emissions — hydrogen is a leading candidate for decarbonizing carbon-intensive and otherwise hard-to-abate sectors like cargo shipping and long-haul trucking.  

Hydrogen can also be used to store energy for longer than current battery technology allows. Wind turbines and solar cells generate cheap renewable energy, but that energy is also variable. Storing energy for when the wind isn’t blowing and the sun isn’t shining is key to creating a stable, clean grid. By using renewable energy sources to make hydrogen that can later be used to produce electricity, the gas can essentially store renewable energy for long periods of time.  

United States Energy Department chief Jennifer Granholm calls clean hydrogen the “‘Swiss Army Knife’ of zero-carbon solutions because it can do just about everything.”  

But now here’s the rub.  

Hydrogen burns clean but the current ways of producing the gas itself generate significant amounts of greenhouse gas emissions. Hydrogen production today produces 1.1 to 1.3 billion metric tons of greenhouse gas emissions, according to the IEA. That’s a smidge over 2% of the 50.6 gigatons of greenhouse gases the world emits each year, according to a September estimate from the Rhodium Group.  

Currently, 95% of hydrogen made in the U.S. is produced by applying super-hot steam, between 1,292- and 1,832-degrees Fahrenheit, to natural gas. Globally, 62% of hydrogen is made with natural gas, 21% is made with coal and 16% is made as a byproduct of other, largely oil and gas related, processes. 

Other, cleaner ways to make the gas are in the early stages of development. A device called an electrolyzer splits water into oxygen and hydrogen with electricity (essentially the opposite of a fuel cell). A key caveat here is the electricity powering the electrolyzer must be clean to ensure the hydrogen generated is also clean.  

It is also possible to make low-carbon intensity hydrogen with natural gas if carbon capture technology is affixed to the natural gas plant where hydrogen is being produced. The energy powering the carbon capture tech must also be clean and methane leaks in the natural gas supply chain must be minimal.  

Globally, just 0.7% of all hydrogen production is considered low-emission, and most of that hydrogen is made with carbon capture tech, according to the IEA.  

Because producing hydrogen takes significant amounts of energy and generates significant quantities of greenhouse gas emissions (with today’s in-use technologies), it hasn’t, so far, been considered a viable source of clean electricity.

From a climate perspective, the impetus to generate hydrogen in cleaner ways has been twofold: To replace the dirty hydrogen humanity already depends on for industrial processes, like making fertilizer, and as a new solution for specific climate problems, like long-haul trucking and seasonal energy storage, where there aren’t other low carbon solutions at scale. 

The newest potential piece of this hydrogen puzzle is the search for the kind under our feet. Rather than producing hydrogen, some scientists, innovators and investors are chasing geologic (or naturally occurring) hydrogen beneath the surface of the Earth.  

If we can find and excavate significant quantities of this naturally occurring hydrogen, that has the potential to change how hydrogen is used in a low-carbon future.  

That’s the topic of a U.S. Senate hearing set for today, and an upcoming story at Cipher, so stay tuned.