Demand is growing for hydrogen-making electrolyzers. What exactly are they?

Washington D.C. Correspondent
An illustration with a blue background showing a contraption in green in the foreground that has an electronic-looking device on the left and a bottle on the right, the two are connected by a thin tube and there's
Ohmium's tabletop demonstration of how an electrolyzer works: Electricity causes water streaming through two metal plates (left) to split into oxygen and hydrogen, with the latter captured in the bottle (right). Photo by Amena H. Saiyid. Illustration by Nadya Nickels.

SAN JOSE, California — With the flick of a switch, water streams through two metal plates atop a table, splitting into oxygen and hydrogen, the latter bubbling into a small clear bottle.

What I witnessed in the corner of a large warehouse space across the bay from San Francisco was a tabletop demonstration of how the California-based company Ohmium and others are using electricity to split water through a chemical process known as electrolysis. Coined by scientist Michael Faraday in the 19th century, electrolysis combines “electro,’ meaning electricity and “lysis” from Greek, meaning to “split, loosen or set free.”

The devices that carry out electrolysis, like the one bubbling out hydrogen on the table, are called electrolyzers. When an electrolyzer is powered by clean, renewable energy, it produces carbon-free, or “green,” hydrogen, which can be used to replace emissions-producing fossil fuels in a range of sectors where direct electricity is not a likely option, like steel, cement and shipping.

Less than 1% of the hydrogen made in the U.S. today is from renewable power. Most is made by heating natural gas with ultra-hot steam, producing unchecked carbon dioxide emissions, in a process termed steam-methane reformation. Efforts to mitigate the emissions from making this kind of hydrogen using carbon capture and storage technology are just getting off the ground.

Still, the United States aims to make 10 million metric tons of clean hydrogen annually by 2030 — and that push is fueling efforts to make hydrogen using electrolysis powered by renewables. It’s going to take a lot of electrolyzers.

“Electrolyzers are the heart of the green hydrogen ecosystem, pieces of the same puzzle really. Without the former, you can’t have the latter,” Rasool Aghatehrani, Ohmium’s chief marketing and strategy officer, explained during my visit in July.

Promising varieties

The first electrolyzers used to make hydrogen date back to the late 18th century. Norway-based Nel Hydrogen’s parent company, Norsk Hydro, commercialized electrolyzers after World War I for fertilizer production, Constantine Levoyannis, head of government affairs for Nel Hydrogen, told Cipher. Electrolyzers also have been used in submarines since World War II to produce oxygen, he said.

Now, developers are trying to harness this technology to make renewable hydrogen at scale for industries that will require a continuous and ample supply of the gas. First, they have to figure out how to make electrolyzers cheaply and efficiently.

Today, at least a dozen companies are making renewable electrolyzer technology for the U.S. market, including Bloom Energy, Nel Hydrogen, Topsoe and Electric Hydrogen, according to Cipher’s Cleantech Tracker.

The Tracker analyzes data from a larger project led by research firm Rhodium Group and the Massachusetts Institute of Technology’s Center for Energy and Environmental Policy Research. Ohmium isn’t on the map because its electrolyzer production is based in India; the company’s research and development is based near its headquarters in Newark, California.

Electrolyzers come in different shapes and sizes. At Bloom Energy’s factory in Fremont, California, which I also visited in July, the factory floor is full of glass cubicles lined up in rows, where assembly line workers clad in blue coats and safety goggles oversee the automated manufacture and assembly of floppy disk-sized cells, where the electrolysis process occurs.

Hundreds of those cells are then housed inside a single industrial container about the size of a refrigerator.

A Bloom Energy official lifts the door of an industrial fridge sized electrolyzer at the Ames National Laboratory in Mountain View, California.

Bloom Energy business development director for hydrogen Akhil Batheja lifts the door of one of the 32 units making up the 4 megawatt solid electrolyzer site at Ames National Laboratory in Mountain View, California in July 2024. Photo by Amena H. Saiyid.

At Ohmium’s headquarters, meanwhile, the easily replaceable electrolyzer components are stacked like a tower of pizza boxes in large metal lockers that could almost be at home in a high-school hallway and could be deployed in a refinery, steel or fertilizer plant.

At least four main commercial electrolyzer technologies currently exist, each with its own set of opportunities and challenges:

  • Alkaline electrolyzers are the most widely used and mature machines on the market today, built mostly in China. They are low-cost and can be made with widely available materials. A majority of this type operate at low temperatures and room pressure and are larger in size than other versions of this technology. Such electrolyzers also ramp up to full operating capacity more slowly than other types.
  • Proton exchange membrane (PEM) electrolyzers like the ones Nel Hydrogen, Electric Hydrogen and Ohmium are building can come in multiple shapes and sizes. Ohmium’s electrolyzer is smaller and can be stacked and arranged like Lego pieces. PEM electrolyzers can quickly ramp production up and down, but they typically use expensive platinum and iridium that are becoming challenging to source. All three companies are either exploring or already starting to use cheaper alternatives.
  • Solid oxide electrolyzers, such as the ones produced by Bloom Energy and Topsoe, can be made with inexpensive materials like nickel and ceramics, making them easier to produce at scale to meet demand. This technology also needs exceedingly high temperatures, ranging from 1,292- to 1,562-degrees Fahrenheit. That heat can be secured from myriad combined sources, including nuclear power plants, waste heat from ammonia and steel production, as well as internal heaters and self-generated heat from the electrolyzer itself.
  • Anion exchange membrane water electrolyzers fall between alkaline and PEM in terms of cost and can ramp up with renewables output, but their equipment and materials may break down with normal wear-and-tear faster than other types of electrolyzers, according to a Columbia University Center for Global Energy Policy paper.

How efficiently each type of electrolyzer uses electricity to produce a kilogram varies, said Anne-Sophie Corbeau, global research scholar with Columbia University’s Center on Global Energy Policy, whose research shows the solid oxide electrolyzer is the most efficient of the four main types.

While Chinese companies focus on traditional alkaline electrolyzers, companies operating in the U.S. are largely focusing on PEMs and solid oxide electrolyzers, though some companies like Nel Hydrogen are making alkaline ones, too.

Ohmium executives opening doors of their electrolyzer units to reveal their closely guarded technology.

Ohmium’s chief marketing and strategy officer Rasool Aghatehrani and vice president for marketing Karina Alexanyan open the doors to the company’s locker-sized electrolyzer units at company headquarters in Newark, California in July 2024. Photo by Amena H. Saiyid.

The critical challenge, Levoyannis told Cipher, will be scaling production of renewable hydrogen enough to drive up demand for electrolyzers and lower the costs of the electrolyzer equipment.

Cost questions

Currently, renewable hydrogen costs upward of $5 per kilogram. The U.S. Energy Department aims to bring the cost down to $1/kg, but developers acknowledge that goal cannot be met without federal subsidies.

Topsoe has received $135.9 million in federal tax credits, for example, to build an electrolyzer factory in a suburb of Richmond, Virginia expected to come online within the next four years, pending the final investment decision. Bloom Energy has received $75 million in credits to expand its factory in Fremont, California and Electric Hydrogen has received $65 million to date for its manufacturing facility in Devens, Massachusetts.

A group of people wearing yellow safety vests gather under a sign that says "Bloom Energy: World's Most Efficient Electrolyzer and Largest Solid Oxide System."

Bloom Energy development and engineering team members reviewing electrolyzer project in Mountain View, California in May 2023. Photo by Bloom Energy.

The economics of renewable hydrogen also depend on where hydrogen will be used and whether electricity from renewables is cheaper than making hydrogen from natural gas with CCS in that region, Corbeau told Cipher.

Since the passage of the 2022 Inflation Reduction Act, investment in manufacturing electrolyzers has risen 142% to $634 million, according to a recent analysis by the Clean Investment Monitor.

Electrolyzer production could climb significantly as the supporting infrastructure to store and transport hydrogen is built out and the U.S. Internal Revenue Service finalizes its guidance — expected by year’s end — on subsidies to offset the cost of renewable-powered electrolysis, Ravi Prasher, Bloom Energy’s chief technology officer, told Cipher.

Once the framework for producing renewable hydrogen becomes clear, “it will allow us to produce and sell more [electrolyzers],” said Levoyannis of Nel Hydrogen.

And that would open up a whole new market for hydrogen.

Editor’s note: Electric Hydrogen’s investors include Breakthrough Energy Ventures, a project of Breakthrough Energy, which also supports Cipher. 

Editor’s note: Electric Hydrogen’s manufacturing facility is in Devens, Massachusetts. An earlier version of this story said it was in Natick, Massachusetts.