Given the need for clean, sustainable energy, researchers around the world have recently started exploring the use of sunlight to create alternative fuels in a process called water splitting. This method, if perfected, would change energy consumption as we know it.
The water splitting method essentially uses sunlight and a photocatalyst (a material that helps complete a reaction in the presence of light) to split water (H2O) into hydrogen (H2) and oxygen (O2), both of which can later be used for fuel.
The process is not yet available on the market, because it lacks efficiency and is expensive to execute.
A new study published in the Canadian Journal of Physics found that distorting the surface of a nanoparticle photocatalyst in a specific way creates “dangling bonds”, which allow water molecules to attach to it, resulting in increased efficiency of the chemical reaction that splits water.
“Recently researchers have shown that tiny particles of the black solid cobalt oxide specifically shaped into spheroids six nanometres in diameter are able to split water into hydrogen and oxygen when added to water and exposed to sunlight,” explains Dr. Nelson of St. Cloud State University, lead author of the study.
“This result is not found when a normal bulky cobalt oxide is used, meaning the substance’s size and shape must affect its ability to split water. Other experiments have also shown that inducing a dipole on the surface of metal oxides affects their ability to absorb light and therefore split water.”
Wanting to dig deeper into which particle shapes lead to the most efficient possible water splitting, Dr. Nelson and colleague Dr. Fang built a theoretical model of cobalt oxide molecules mixing with water molecules in the presence of sunlight.
Nelson and Fang found that “theoretically, if we modify the surface of the tiny cobalt oxide spheroids by changing the angles at which oxygen is bonded to cobalt within them, open bonding sites—the dangling bonds—are created, and water molecules can come in and attach to them.”
“The resulting material has a dipole, which is important for helping it absorb the sunlight it is exposed to, which then gives the final push needed to split water into hydrogen and oxygen,” adds Nelson.
The study found 3.3⁰ was the magic angle that led to the most efficient use of sunlight in the reaction; that is, the angle between cobalt and oxygen in the spheroids needs to be 3.3⁰ for the highest reaction efficiency.
“These results will hopefully help researchers design future experiments. I would also like to combine this work with a model I did for zinc oxide nanoparticles to further understand how to improve efficiency with other materials,” says Nelson.
Continued studies to improve efficiency of water splitting are still necessary; real-world applications of water splitting would help abate our reliance on non-renewable resources for fuel and reduce climate change emissions by unprecedented amounts.
Read the paper: Tight binding model of induced band shift in CoO nanoparticles in the Canadian Journal of Physics.
