From Tesla’s Elon Musk to European Commission President Ursula von der Leyen, the past few years have seen many high-profile names talk about the role hydrogen may — or may not — play in the planet’s shift to a more sustainable future.

Musk has expressed skepticism about hydrogen’s usefulness, but many think it could help to slash emissions in a number of sectors, including transportation and heavy industry.   

While there’s a major buzz about hydrogen and its importance as a tool in securing a low-carbon future — a topic that’s generated a lot of debate in recent months — the vast majority of its production is still based on fossil fuels.

Indeed, according to a Sept. 2022 tracking report from the International Energy Agency, low-emission hydrogen production in 2021 accounted for less than 1% of global hydrogen production.

If it’s to have any role in the planned energy transition, then hydrogen generation needs to change in a pretty big way.   

“The first thing to say is that hydrogen doesn’t really exist naturally, so it has to be produced,” said Rachael Rothman, co-director of the Grantham Centre for Sustainable Futures at the University of Sheffield.

“It has a lot of potential to help us decarbonize going forwards, but we need to find low-carbon ways of producing it in the first place,” she said, adding that different methods of production had been “denoted different colors.”

“About 95% of our hydrogen today comes from steam methane reforming and has a large associated carbon footprint, and that’s what’s called ‘grey’ hydrogen,” Rothman told CNBC.

Grey hydrogen is, according to energy firm National Grid, “created from natural gas, or methane.” It says that the greenhouse gases associated with the process are not captured, hence the carbon footprint that Rothman refers to.

The dominance of such a method is clearly at odds with net-zero goals. As a result, an array of sources, systems and colors of hydrogen are now being put forward as alternatives.

These include green hydrogen, which refers to hydrogen produced using renewables and electrolysis, with an electric current splitting water into oxygen and hydrogen.

Blue hydrogen, on the other hand, indicates the use of natural gas — a fossil fuel — and carbon capture utilization and storage. There has been a charged debate around the role blue hydrogen could play in the decarbonization of society.

Alongside blue and green, another color attracting attention is pink. Like green hydrogen, its process incorporates electrolysis, but there’s a key difference: pink uses nuclear.

“If you split … water, you get hydrogen and oxygen,” Rothman said. “But splitting water takes energy, so what pink hydrogen is about is splitting water using energy that has come from nuclear.”

This means that “the whole system is low carbon, because … there’s no carbon in water … but also the energy source is also very low carbon because it’s nuclear.”

Alongside electrolysis, Rothman noted that nuclear could also be used with something called a thermochemical cycle.

This, she explained, harnessed very high temperatures to split water into oxygen and hydrogen. 

Pink hydrogen already has some potentially significant backers. These include EDF Energy, which has floated the idea of producing hydrogen at Sizewell C, a 3.2-gigawatt nuclear power station planned for the U.K.

“At Sizewell C, we are exploring how we can produce and use hydrogen in several ways,” the firm’s website says. “Firstly, it could help lower emissions during construction of the power station.”

“Secondly, once Sizewell C is operational, we hope to use some of the heat it generates (alongside electricity) to make hydrogen more efficiently,” it adds.

EDF Energy, which is part of the multinational EDF Group, said in a statement sent to CNBC: “Hydrogen produced from nuclear power can play a substantial role in the energy transition.”

The company also acknowledged there were challenges facing the sector and its development.

“Hydrogen is currently a relatively expensive fuel and so the key challenge for low carbon electrolytic hydrogen, whether produced from renewable or nuclear energy, is to bring down the costs of production,” it said.

This needed “supportive policies which encourage investment in early hydrogen production projects and encourage users to switch from fossil fuels to low carbon hydrogen.”

“Growing the market for low carbon hydrogen will deliver the economies of scale and “learning by doing” which will help to reduce the costs of production.”

While there is excitement about the role nuclear could play in hydrogen production and the wider energy transition — the IEA, for example, says nuclear power has “significant potential to contribute to power sector decarbonisation” — it goes without saying that it’s not favored by all.

Critics include Greenpeace. “Nuclear power is touted as a solution to our energy problems, but in reality it’s complex and hugely expensive to build,” the environmental organization says. “It also creates huge amounts of hazardous waste.”

A multi-colored future?

During her interview with CNBC, the University of Sheffield’s Rothman spoke about the bigger picture and the role different types of hydrogen might play. Could we ever see a time when the level of blue and grey hydrogen drops to zero?

“It depends how long a timeframe you’re looking at,” she said, adding that “in an ideal world, they will eventually drop very low.”

“Ultimately, we ideally get rid of all of our grey hydrogen, because grey hydrogen has a large carbon footprint and we need to get rid of it,” Rothman said.

“As we improve carbon capture and storage, there may be a space for blue hydrogen and that’s yet to be evaluated, depending on the … developments there.”

“The pink and green we know there has to be a space for because that’s where you really get the low carbon [hydrogen], and we know it should be, it’s possible to get there.”

Fiona Rayment, chief scientist at the UK National Nuclear Laboratory — which, like EDF Energy, is a member of trade association Hydrogen UK — pressed home the importance of having a range of options available in the years ahead.

“The challenge of net zero cannot be underestimated; we will need to embrace all sources of low carbon hydrogen generation to replace our reliance on fossil fuels,” she told CNBC.

While there has been a lot of talk about using colors to differentiate the various methods of hydrogen production, there is also a lively discussion about whether such a classification system should even exist at all.

“What we want is low carbon hydrogen,” Rothman said. “And I know there is a lot of confusion about the various colors, and I’ve heard some people say … ‘why do we even have the colors, why do we not just have hydrogen and low carbon hydrogen?'”

“And ultimately, it’s the low carbon bit that’s important, and both pink and green would do that.”