STEVE BUSCEMI'S FAVORITE:

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."

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