Pulling electricity from the air with a hydrogen-eating enzyme

We could use green hydrogen to store and transport renewable energy, but at the moment, it’s still hard to make and convert into electricity at a commercial scale.

But what if nature’s already doing the job for us?

An Australian-led research team has found an enzyme that can suck hydrogen out of the air and convert it into electricity, at a very efficient rate.

The enzyme comes from a soil-dwelling bacterium called Mycobacterium smegmatis.

“We’ve known for some time that bacteria can use the trace hydrogen in the air as a source of energy to help them grow and survive, including in Antarctic soils, volcanic craters, and the deep ocean,” says Professor Chris Greening, from the Monash University Biomedicine Discovery Institute.

This led to a theory: there should be a protein (or enzyme) in bacteria that could absorb hydrogen for energy.

“We knew there must be an enzyme to do this,” says Dr Rhys Grinter, also from Monash.

“So we worked out the chemistry that was required to isolate it, managed to isolate it, and showed that the enzyme itself can turn hydrogen in the air into small amounts of electricity.”

Grinter says that it took nearly five years to find the enzyme, which they’ve called Huc, and show that it worked.

“There was quite a few dead ends that we tried first. There was no roadmap for doing this. We were just kind of figuring out as we went along.”

The enzyme, and how it absorbs hydrogen. Credit: Monash University

Once they had found Huc and shown that it was the enzyme that absorbed hydrogen, the researchers used electron microscopy to establish its shape.

This let them figure out Huc’s mechanism: how it worked its hydrogen magic.

They also used a technique called electrochemistry to figure out how good it was at making electricity.

“Huc is extraordinarily efficient,” says Grinter.

“Unlike all other known enzymes and chemical catalysts, it even consumes hydrogen below atmospheric levels – as little as 0.00005% of the air we breathe.”

Rhys grinter in lab
Dr Rhys Grinter. Credit: Monash University

It can also be stored in its purified form for a long time.

“It is astonishingly stable. It is possible to freeze the enzyme or heat it to 80°C, and it retains its power to generate energy,” says Ashleigh Kropp, a PhD student at Monash.

The catch? At the moment, the researchers have only shown that a small amount of the enzyme can generate an equally small amount of electricity.

But they think they can use enough of it to power small devices: the bacteria that makes Huc are easy to grow in large quantities.

“We’re confident, based on other work that has been done with catalysts, that if we scale that up and put it into an electric device, we could use it to power something like a wristwatch as a proof of concept,” says Grinter.

If enough of the enzyme could be made industrially, it could even be a useful component of much bigger hydrogen fuel cells – like for a car.

“I don’t see a fundamental barrier,” says Grinter.

“It would just be developing enough of the density of the enzyme on a surface that it could catalyse the hydrogen. So it’s a long term possibility, but I would say it’s a possibility.”

That said, scaling the enzyme up like this will take years of work – and more funding.

“It would be really nice to get seed funding and give significant investment of capital to really kickstart the process,” says Grinter.

They’ve published their findings in Nature.

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