EMORY (US)—Chemists have developed what they say is the most potent homogeneous catalyst known for water oxidation, considered a crucial component for generating clean hydrogen fuel using only water and sunlight.
In order to be viable, a water oxygen catalyst (WOC) needs selectivity, stability, and speed. Homogeneity is also a desired trait, since it boosts efficiency and makes the WOC easier to study and optimize.
The new WOC has all of these qualities, and is based on the cheap and abundant element cobalt, adding to its potential to help solar energy go mainstream.
This “has really upped the standard from the other known homogeneous WOCs,” says Craig Hill, an inorganic chemist at Emory University.
“It’s like a home run compared to a base hit.”
The study, published online in Science, was made in collaboration with the Paris Institute of Molecular Chemistry.
The WOC research is a component of the Emory Bio-inspired Renewable Energy Center, that aims to mimic natural processes such as photosynthesis to generate clean fuel.
The next step involves incorporating the WOC into a solar-driven, water-splitting system, researchers say.
The long-term goal is to use sunlight to split water into oxygen and hydrogen so it becomes the fuel. Its combustion produces the by-product of water—which flows back into a clean, green, renewable cycle.
Three main technical challenges are involved, Hill says: developing a light collector, a catalyst to oxidize water to oxygen, and a catalyst to reduce water to hydrogen.
“We are aiming for a WOC that is free of organic structure, because organic components will combine with oxygen and self-destruct. You’ll wind up with a lot of gunk.”
Enzymes are nature’s catalysts. The enzyme in the oxygen-evolving center of green plants “is about the least stable catalyst in nature, and one of the shortest lived, because it’s doing one of the hardest jobs,” Hill explains.
“We’ve duplicated this complex natural process by taking some of the essential features from photosynthesis and using them in a synthetic, carbon-free, homogeneous system.
The result is a water oxidation catalyst that is far more stable than the one found in nature.”
Two years ago, Hill’s lab and collaborators developed the first prototype of a stable, homogenous, carbon-free WOC. But it was based on ruthenium, a relatively rare and expensive element.
Building on that work, the researchers began experimenting with the cheaper and more abundant element cobalt, which proved even faster than the ruthenium version for light-driven water oxidation.
Emory University science news: www.emory.edu/esciencecommons