Capturing or otherwise neutralizing the CO2 must be done safely, says Stephen Wallace, who runs a microbiology lab at the University of Edinburgh. But he adds that Cemvita Factory’s idea of harnessing microbes for hydrogen production is “indicative of a lot of the really interesting work going on in biotechnology right now.” Wallace and his colleagues are themselves experimenting with bioreactors and have had some success in getting microbes to yield hydrogen from things like moldy bread or the lignin in paper industry waste.
But while some microbes help produce hydrogen, others are the scourge of these projects, as they can eat up stored hydrogen or consume the gas in natural wells, says Jon Gluyas, a geologist at Durham University. “We’re trying to keep bacteria away from our hydrogen because they love feasting on it,” he explains.
And he has another quibble. He argues that “gold hydrogen” is different from what Cemvita Factory is proposing. To Gluyas, that term refers specifically to hydrogen that has been produced naturally underground. He should know. “I named it,” he says. That Cemvita has given the same name to its hydrogen—which, the company makes clear, is “produced biologically, by microbes, and through a human-driven process”—is just a “coincidence,” Karimi claims.
For more than a century, geologists have been pondering how much of the natural hydrogen to which Gluyas refers could be freely available in the ground beneath our feet. The German scientist Ernst Erdmann described in 1910 how he had detected an outflow of hydrogen at a salt mine and tracked it for four and a half years. But the possibility of widespread subterranean sources was still poorly understood, even into the 1980s, says Barbara Sherwood Lollar, a geologist at the University of Toronto.
She recalls surveying sites for gases back then and realizing that significant volumes of hydrogen were present in the ground. “Good lord, it was hydrogen, these rocks were full of hydrogen,” she remembers. Yes, the Earth has bubbles. Since then, she and colleagues have mapped the locations of potential hydrogen sources—based on geology and known deposits—around the world.
Different processes can give rise to natural hydrogen wells. One example is radiolysis, in which subatomic particles naturally emitted by radioactive rocks such as granite cause certain molecules to break apart, releasing hydrogen. In general, hydrogen is associated with crystalline rocks, rather than sedimentary ones.
But as Gluyas mentions, microbes often gobble up hydrogen formed in the ground before anyone has had the chance to siphon it off. So the tricky part is finding a subterranean hydrogen source that is both large and intact. “No one, I think, can pronounce on whether or not these accumulations of hydrogen within the crystalline rocks … will be viable at scale,” says Sherwood Lollar.
Some firms are already targeting hydrogen deposits, though—such as the company Gold Hydrogen in Australia. It estimates that there could be a total of 1.3 billion kilograms of hydrogen at depths of around 500 meters in the Ramsay Peninsula and Kangaroo Island in South Australia. There is also a large and well-known source of hydrogen in Mali. Both this and the Australian deposits are associated with “fairy circles”—where bare patches in the middle of vegetation indicate that hydrogen is coming out of the ground. Commercial extraction of hydrogen from any such locations, at scale, has yet to happen.