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Green-steel startup Boston Metal just showed that it has all the ingredients needed to make steel without emitting gobs of greenhouse gases. The company successfully ran its largest reactor yet to make steel, producing over a ton of metal, MIT Technology Review can exclusively report.

The latest milestone means that Boston Metal just got one step closer to commercializing its technology. The company’s process uses electricity to make steel, and depending on the source of that electricity, it could mean cleaning up production of one of the most polluting materials on the planet. The world produces about 2 billion metric tons of steel each year, emitting over 3 billion metric tons of carbon dioxide in the process.

While there are still a lot of milestones left before reaching the scale needed to make a dent in the steel industry, the latest run shows that the company can scale up its process.

Boston Metal started up its industrial reactor for steelmaking in January, and after it had run for several weeks, the company siphoned out roughly a ton of material on February 17. (You can see a video of the molten metal here. It’s really cool.)

Work on this reactor has been underway for a while. I got to visit the facility in Woburn, Massachusetts, in 2022, when construction was nearly done. In the years since, the company has been working on testing it out to make other metals before retrofitting it for steel production. 

Boston Metal’s approach is very different from that of a conventional steel plant. Steelmaking typically involves a blast furnace, which uses a coal-based fuel called coke to drive the reactions needed to turn iron ore into iron (the key ingredient in steel). The carbon in coke combines with oxygen pulled out of the iron ore, which gets released as carbon dioxide.

Instead, Boston Metal uses electricity in a process called molten oxide electrolysis (MOE). Iron ore gets loaded into a reactor, mixed with other ingredients, and then electricity is run through it, heating the mixture to around 1,600 °C (2,900 °F) and driving the reactions needed to make iron. That iron can then be turned into steel. 

Crucially for the climate, this process emits oxygen rather than carbon dioxide (that infamous greenhouse gas). If renewables like wind and solar or nuclear power are used as the source of electricity, then this approach can virtually cut out the climate impact from steel production. 

MOE was developed at MIT, and Boston Metal was founded in 2013 to commercialize the technology. Since then, the company has worked to take it from lab scale, with reactors roughly the size of a coffee cup, to much larger ones that can produce tons of metal at a time. That’s crucial for an industry that operates on the scale of billions of tons per year.

“The volumes of steel everywhere around us—it’s immense,” says Adam Rauwerdink, senior vice president of business development at Boston Metal. “The scale is massive.”

Making the huge amounts of steel required to be commercially relevant has been quite the technical challenge. 

One key component of Boston Metal’s design is the anode. It’s basically a rounded metallic bit that sticks into the reactor, providing a way for electricity to get in and drive the reactions required. In theory, this anode doesn’t get used up, but if the conditions aren’t quite right, it can degrade over time.

Over the past few years, the company has made a lot of progress in preventing inert anode degradation, Rauwerdink says. The latest phase of work is more complicated, because now the company is adding multiple anodes in the same reactor. 

In lab-scale reactors, there’s one anode, and it’s quite small. Larger reactors require bigger anodes, and at a certain point it’s necessary to add more of them. The latest run continues to prove how Boston Metal’s approach can scale, Rauwerdink says: making reactors larger, adding more anodes, and then adding multiple reactors together in a single plant to make the volumes of material needed.

Now that the company has completed its first run of the multi-anode reactor for steelmaking, the plan is to keep exploring how the reactions happen at this larger scale. These runs will also help the company better understand what it will cost to make its products.

The next step is to build an even bigger system, Rauwerdink says—something that won’t fit in the Boston facility. While a reactor of the current size can make a ton or two of material in about a month, the truly industrial-scale equipment will make that amount of metal in about a day. That demonstration plant should come online in late 2026 and begin operation in 2027, he says. Ultimately, the company hopes to license its technology to steelmakers. 

In steel and other heavy industries, the scale can be mind-boggling. Boston Metal has been at this for over a decade, and it’s fascinating to see the company make progress toward becoming a player in this massive industry. 

Now read the rest of The Spark

Related reading

We named green steel one of our 2025 Breakthrough Technologies. Read more about why here.

I visited Boston Metal’s facility in Massachusetts in 2022—read more about the company’s technology in this story (I’d say it pretty much holds up). 

Climate tech companies like Boston Metal have seen a second boom period for funding and support following the cleantech crash a decade ago. Read more in this 2023 feature from David Rotman. 

Another thing

Electricity demand is rising faster in the US than it has in decades, and meeting it will require building new power plants and expanding grid infrastructure. That could be a problem, because it’s historically been expensive and slow to get new transmission lines approved. 

New technologies could help in a major way, according to Brian Deese and Rob Gramlich. Read more in this new op-ed. 

And one more

Plants have really nailed the process of making food from sunlight in photosynthesis. For a very long time, researchers have been trying to mimic this process and make an artificial leaf that can make fuels using the sun’s energy.

Now, researchers are aiming to make energy-dense fuels using a specialized, copper-containing catalyst. Read more about the innovation in my colleague Carly Kay’s latest story. 

Keeping up with climate

Energy storage is still growing quickly in the US, with 18 gigawatts set to come online this year. That’s up from 11 GW in 2024. (Canary Media)

Oil companies including Shell, BP, and Equinor are rolling back climate commitments and ramping up fossil-fuel production. Oil and gas companies were accounting for only a small fraction of clean energy investment, so experts say that’s not a huge loss. But putting money toward new oil and gas could be bad for emissions. (Grist)

Butterfly populations are cratering around the US, dropping by 22% in just the last 20 years. Check out this visualization to see how things are changing where you live. (New York Times)

New York City’s congestion pricing plan, which charges cars to enter the busiest parts of the city, is gaining popularity: 42% of New York City residents support the toll, up from 32% in December. (Bloomberg)

Here’s a reality check for you: Ukraine doesn’t have minable deposits of rare earth metals, experts say. While tensions between US and Ukraine leaders ran high in a meeting to discuss a minerals deal, IEEE Spectrum reports that the reality doesn’t match the political theater here. (IEEE Spectrum)

Quaise Energy has a wild drilling technology that it says could unlock the potential for geothermal energy. In a demonstration, the company recently drilled several inches into a piece of rock using its millimeter-wave technology. (Wall Street Journal)

Here’s another one for the “weird climate change effects” file: greenhouse-gas emissions could mean less capacity for satellites. It’s getting crowded up there. (Grist)

The Biden administration funded agriculture projects related to climate change, and now farmers are getting caught up in the Trump administration’s efforts to claw back the money. This is a fascinating case of how the same project can be described with entirely different language depending on political priorities. (Washington Post)

You and I are helping to pay for the electricity demands of big data centers. While some grid upgrades are needed just to serve big projects like those centers, the cost of building and maintaining the grid is shared by everyone who pays for electricity. (Heatmap)