Breakthrough Energy Ventures led a $20 million funding round in Boston Metal, which is developing a process to reduce carbon emissions in steel making by using electricity instead of traditional pollution-heavy techniques.

Iron and steel manufacturing results in 1.7 billion metric tons of carbon dioxide emissions annually, or more than the emissions from 360 million passenger cars, according to a study published in Science in June.

Typically, steel is made by burning iron oxide with coke, a carbon-rich fuel made from coal.

“Most metals are in nature as a form of oxide,” explains Tadeu Carneiro, chief executive of Boston Metal. “In order to get the metal, you have to break the bonds in the oxide and free the metal from it. When you do that with carbon, you generate CO2.”

Boston Metal uses a process called metal oxide electrolysis, which allows pure metals to be produced without carbon emissions. The only byproduct is oxygen.

The process uses a “soup of oxides,” Carneiro told Fortune. “Depending on the metal you want to produce, you have a different soup of oxides.”

The other oxides in the mixture must be relatively stable so that when electricity is introduced to the electrolytic cell—the container in which the metal is reduced—the desired metal pools in a pure liquid form at the bottom. The cell is tapped every so often to extract the metal, the hole is plugged, and the process continues.

Carneiro says the process is not yet commercially available, but will be cost-competitive with traditional techniques. Furthermore, while electricity is getting cheaper, he added, coal costs are rising, potentially making Boston Metal’s technique a more affordable option in the future.

Certain materials must be added to the liquid metal after it’s reduced by Boston Metal’s process to meet industry specifications. Steel, for example, includes iron, carbon, and other elements.

In theory, the entire steel manufacturing process—from the power plant supplying the electricity to the steel manufacturing itself—could become carbon-free. But that’s a long way off considering that most power plants today rely on fossil fuels, not renewable energy.

Boston Metal hopes to change that with its novel technology. Prof. Donald R. Sadoway of MIT latched onto the idea of metal oxide electrolysis, or MOE, as part of a NASA research competition to extract oxygen from lunar rocks. After proposing the use of an electrolytic cell to break the oxygen compounds from rocks, producing molten metal, Sadoway considered the potential for the technology on Earth.

He founded the Boston Electrometallurgical, now known as Boston Metal, with Antoine Allanore and Jim Yurko in 2012. A year later, Sadoway published a paper with two colleagues demonstrating that MOE could produce emissions-free steel, and the company gained its first investor: Ingo Wender, the founder and president of Terrativa Minerais, a Brazil-based mining venture company, and founder of Advanced Potash Technologies, a fertilizer company.

With grants from the Defense Department, Energy Department, and National Science Foundation, Boston Metal had enough funding early on—$12 million—to develop its first semi-industrial cell to demonstrate its technology.

“Now we need to develop industrial cells for specific metals,” said Carneiro. Over the next three years, Boston Metal aims to develop a demonstration plant to manufacture 1,000 tons of ferrovanadium annually. This alloy can be added to steel as a hardener, and will be Boston Metal’s first industrial-scale venture.

With its latest round of funding, Boston Metal plans to go commercial and hire more engineers.

Aside from Breakthrough Energy Ventures, the latest funding round also included Prelude Ventures and MIT offshoot The Engine, bringing its total funding raised to $32 million.

“A critical piece to achieving a carbon-free world is the decarbonization of steel production,” said Katie Rae, managing partner and CEO of The Engine. “Boston Metal has spent years developing its groundbreaking technology and is incredibly close to bringing it to market.”

Carmichael Roberts, a partner with Breakthrough Energy Ventures, said that Boston Metal “has the potential to decarbonize the massive steel manufacturing industry, and economically deliver a set of high-quality products on a global scale.”

The investment is an example of Breaththrough Energy Ventures’ focus on startups that can reduce carbon emissions. Previous investments include a fusion energy company, a battery maker, and another working on geothermal power.

According to Carneiro, Boston Metal is already working with several unidentified companies that have an eye of becoming its first customers.

“The metals industry tends to be a very conservative industry and getting rid of CO2 emissions, especially for steel, is a big deal. It’s not a small thing, and therefore this is really revolutionizing,” said Carneiro. “We are on a path to help saving the world.”