For decades, scientists around the world have been searching for ways to use solar energy to generate the key reaction to producing hydrogen as a pure energy source – splitting water molecules to form hydrogen and oxygen. However, such an effort has mostly failed because it was too expensive to do well, and trying to do it at a low cost led to poor performance.
Now, researchers from the University of Texas at Austin have found a cheap way to solve half of the equation by using sunlight to efficiently divide oxygen molecules from water. Found, recently published in Nature communication, represents a step forward towards greater adoption of hydrogen as a key part of our energy infrastructure.
As early as the 1970s, researchers were investigating the possibility of using solar energy to generate hydrogen. However, the inability to find materials with the combination of properties needed for a device that can effectively perform the most important chemical reactions has prevented it from becoming a common method.
“You need materials that are good at absorbing sunlight and at the same time do not degrade while water-splitting reactions take place,” said Edward Yu, a professor at Cockrell School’s Department of Electrical and Computer Engineering. “It turns out that materials that are good at absorbing sunlight tend to be unstable under the conditions required for the water-sharing reaction, while the materials that are stable tend to be poorly absorbing sunlight. These conflicting requirements drive you “Against a seemingly inevitable compromise, but by combining several materials – one that effectively absorbs sunlight, such as silicon, and another that provides good stability, such as silicon dioxide – in a single unit, this conflict can be resolved.”
However, this creates another challenge – the electrons and holes that occur when absorbing sunlight into silicon must be able to move easily over the silicon dioxide layer. This usually requires that the silicon dioxide layer be no more than a few nanometers, which reduces its effectiveness in protecting the silicon absorber from degradation.
The key to this breakthrough came through a method of making electrically conductive paths through a thick layer of silicon dioxide that can be performed at low cost and scaled to high production volumes. To get there, Yu and his team used a technique first used in the production of semiconductor electronic chips. By coating the silicon dioxide layer with a thin film of aluminum and then heating the entire structure, nanoscale “spikes” of aluminum are formed which completely bridge the silicon dioxide layer. These can then be easily replaced by nickel or other materials that help catalyze water-splitting reactions.
When illuminated by sunlight, the devices can efficiently oxidize water to form oxygen molecules, while generating hydrogen at a separate electrode and exhibiting outstanding stability during extended operation. Because the techniques used to make these devices are often used in the production of semiconductor electronics, they should be easy to scale for mass production.
The team has filed a preliminary patent application to commercialize the technology.
Improving the way hydrogen is generated is the key to it emerging as a viable fuel source. Most hydrogen production today takes place through heating of steam and methane, but it is heavily dependent on fossil fuels and produces carbon emissions.
It is being pushed towards “green hydrogen” which uses more environmentally friendly methods to generate hydrogen. And simplifying the water-splitting reaction is an important part of that effort.
Hydrogen has the potential to become an important renewable resource with some unique properties. It already has a major role in important industrial processes, and it is starting to appear in the automotive industry. Fuel cell batteries look promising in long-distance transport, and hydrogen technology can be a boon for energy storage, with the ability to store excess wind and solar energy produced when conditions are ripe for them.
Going forward, the team will work to improve the efficiency of the oxygen portion of water splitting by increasing the reaction rate. The researchers’ next big challenge is then to move on to the second half of the equation.
“We were able to take up the oxygen side of the reaction first, which is the more challenging part,” Yu said, “but you have to perform both the hydrogen and oxygen evolution reactions to completely split the water molecules, so that’s why our next step is to see on using these ideas to create units for the hydrogen part of the reaction. ”
New porous material that promises to create renewable energy from water
Soonil Lee et al., Scalable, highly stable Si-based metal insulator semiconductor photo anodes for water oxidation produced using thin film reactions and electrodeposition, Nature communication (2021). DOI: 10.1038 / s41467-021-24229-y
Provided by the University of Texas at Austin
Citation: Making pure hydrogen is difficult, but researchers just solved a major obstacle (2021, July 19) retrieved July 19, 2021 from https://phys.org/news/2021-07-hydrogen-hard-major-hurdle. html
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