New catalyst can provide cheaper and more efficient production of hydrogen
Researchers at KTH Royal Institute of Technology have participated in developing a new, very effective catalyst for the oxidation of water into oxygen and hydrogen. The results, which have recently been published in the scientific journal Nature Catalysis, can lead to a more efficient production of hydrogen.
”There are two important points in the work. The performance of the catalyst is excellent, it is one of the best candidates for the reaction. The second point is that we clearly explain the reaction mechanism. We propose a new mechanism,” says Hao Yang, Doctoral student at the Department of Chemistry and first author of the article.
Hydrogen has gained great importance when it comes to storing large amounts of energy. The gas has high energy density, which makes it possible to store around 100 times the energy in a lithium battery per weight. It can then be used to extract electricity from, by using fuel cells. One area of use is the steel industry, where hydrogen is part of the production of fossil-free steel.
”We want to produce hydrogen more efficiently. The generation of hydrogen is easy, but the generation of oxygen is more sluggish. You need to overcome a huge energy barrier, and therefore you need a catalyst,” says Hao Yang.
International collaboration
In the project, researchers from KTH have collaborated with Westlake University in Hangzhou, China, where Professor Licheng Sun, who is also active at KTH, is the leader of a research group.
”His group has done the experimental part and we have done simulations. They have produced a material for electrolysis of water, the division of water in oxygen and hydrogen. It is an extremely porous material which is also electrically conductive. By adding small amounts of cobalt, they developed a material with extremely high activity in the oxygen forming reaction, which is considered more difficult,” says Mårten Ahlquist, Professor in Theoretical Catalysis at the Division of Theoretical Chemistry and Biology.
”This material consists of small amounts of cobalt which are scattered throughout the structure. Each cobalt atom works as a catalyst, so you can have extremely small amounts and still get a very high effect.”
Usually, the precious metals iridium and ruthenium are the ones used for the oxidation of water. By using cobalt, you get a cheaper and more efficient alternative.
Through experiments and theoretical simulations to study the reaction mechanisms of the cobalt atoms, the researchers found a new mechanism for the formation of the first bond between two oxygen atoms, which is the reason for cobalt reacting at such a high rates.
”We call it an intramolecular hydroxyl nucleophilic attack. It is a new reaction pathway. We use many techniques to demonstrate this pathway. The fabrication process is straightforward. It can be extended to other catalyst systems by following a similar protocol. You can change elements, center(s) or polymeric substrates. Also, the method we used to understand the mechanism can be extended to other reactions or catalysts,” says Hao Yang.
Serching for cheaper materials
The next target for the researchers is to see if they can reach the same performance with iron or nickel, which is even cheaper than cobalt.
The researchers have also come to understand why many other catalysts need a very high pH value. On the contrary, the new catalyst has proven to work also in an environment of a neutral pH.
“Very high pH conditions are very corrosive, and it is difficult to keep the stability during a long time under such extreme circumstances. A potential application is if you would like to use sea water instead of pure water in the oxidation process. Then, it is an advantage to be able to use the catalyst at a neutral pH”, says Mårten Ahlquist.
Text: Sabina Fabrizi