Scientists say they have developed a highly stable material that helps split water molecules for hydrogen fuel production.
Breaking the bonds between oxygen and hydrogen in water could be a key to the creation of hydrogen in a sustainable manner, but finding an economically viable technique for this has proved difficult, said researchers from the University of Illinois at Urbana-Champaign in the US.
The new hydrogen-generating catalyst, described in the journal Angewandte Chemie, is made from mixing metal compounds with a substance called perchloric acid.
Electrolysers use electricity to break water molecules into oxygen and hydrogen, researchers said.
The most efficient of these devices use corrosive acids and electrode materials made of the metal compounds iridium oxide or ruthenium oxide, they said.
Iridium oxide is the more stable of the two, but iridium is one of the least abundant elements on the Earth, so researchers are in search of an alternative material.
“Much of the previous work was performed with electrolysers made from just two elements — one metal and oxygen,” said Hong Yang, a professor at the University of Illinois.
“In a recent study, we found if a compound has two metal elements — yttrium and ruthenium — and oxygen, the rate of water-splitting reaction increased,” Yang said.
Yao Qin, a former member of Yang’s group, first experimented with the procedure for making this new material by using different acids and heating temperatures to increase the rate of the water-splitting reaction.
The researchers found that when they used perchloric acid as a catalyst and let the mixture react under heat, the physical nature of the yttrium ruthenate product changed.
“The material became more porous and also had a new crystalline structure, different from all the solid catalysts we made before,” said Jaemin Kim, a postdoctoral researcher at the University of Illinois.
The new porous material the team developed — a pyrochlore oxide of yttrium ruthenate — can split water molecules at a higher rate than the current industry standard.
“Because of the increased activity it promotes, a porous structure is highly desirable when it comes to electrocatalysts,” Yang said.
“These pores can be produced synthetically with nanometre-sized templates and substances for making ceramics; however, those can’t hold up under the high-temperature conditions needed for making high-quality solid catalysts,” Yang said.
The team looked at the structure of the new material with an electron microscope and found that it is four times more porous than the original yttrium ruthenate they developed in a previous study, and three times that of the iridium and ruthenium oxides used commercially.
“It was surprising to find that the acid we chose as a catalyst for this reaction turned out to improve the structure of the material used for the electrodes,” Yang said.
“This realisation was fortuitous and quite valuable for us,” he said.
The next steps for the group are to fabricate a laboratory-scale device for further testing and to continue to improve the porous electrode stability in acidic environments, Yang said.