Sunlight and mirrors could extract gas from water and pave way for the expansion of clean hydrogen energy
By Sophie Yeo
Hydrogen could be more widely used as a clean, zero-carbon technology, thanks to a new technology that scientists are calling the “Holy Grail” of a sustainable hydrogen economy.
The radically new technique, developed by researchers at the University of Colorado Boulder, harnesses sunlight to split water into its two components of oxygen and hydrogen molecules, allowing the latter to be collected as hydrogen gas.
“We have designed something here that is very different from other methods and frankly something that nobody thought was possible before,” says Alan Weimer, the co-lead on the team.
“Splitting water with sunlight is the Holy Grail of a sustainable hydrogen economy.”
Hydrogen has been promoted as a sustainable fuel that could be particularly useful in the automotive industry. In February, for instance, a joint report by government and industry suggested that the UK could have 1.6 million hydrogen vehicles on the road by 2030.
The new technology uses a vast network of mirrors to concentrate sunlight onto a single point on top of a tower up to several hundred feet tall.
The tower heats up to around 1,350C. This heat is then delivered into a reactor containing metal oxides, made up of a combination of iron, cobalt, aluminium and oxygen, which releases oxygen atoms.
Adding steam to the system, which can be produced by boiling water in the reactor with the concentrated sunlight, causes oxygen to adhere to the surface of the metal oxide, which then frees up the hydrogen molecules for collection.
This is a big improvement on the previous system of obtaining hydrogen gas, says Charles Musgrave, co-lead on the team.
He says, “”The more conventional approaches require the control of both the switching of the temperature in the reactor from a hot to a cool state and the introduction of steam into the system
“One of the big innovations in our system is that there is no swing in the temperature. The whole process is driven by either turning a steam valve on or off.”
This conventional two-step method for splitting the water wastes both time and heat. “There are only so many hours of sunlight in a day,” he said.
With the new method, the amount of hydrogen produced depends entirely on the amount of metal oxide and how much steam goes into the system.
To produce a significant amount of hydrogen gas would require a number of tall towers to gather sunlight from several acres of mirrors surrounding each tower.
“When we saw that we could use this simpler, more effective method, it required a change in our thinking,” said Weimer.
“We had to develop a theory to explain it and make it believable and understandable to other scientists and engineers.”
But the new technology isn’t enough by itself to make hydrogen the next big thing in the renewables market; Weimar admits that, until there is a change of thinking regarding climate change, commercialisation of their discovery is likely to be years away.
“With the price of natural gas so low, there is no incentive to burn clean energy,” said Weimer.
“There would have to be a substantial monetary penalty for putting carbon into the atmosphere, or the price of fossil fuels would have to go way up.”