A novel category of materials that use light to make hydrogen from water has been developed by Oregon State University researchers, leading to new approaches to transforming the sun’s rays into clean energy.
A team effort led by Kyriakos Stylianou of the OSU College of Science has developed a photocatalyst that can be made use of to produce hydrogen at high efficiency and speed. Hydrogen is used in fuel cells for cars and in manufacturing many chemicals such as ammonia, in refining metals, and in the production of plastics.
A catalyst is an element that boosts the rate of a chemical reaction without itself being permanently changed during the process, Stylianou said. A photocatalyst is a material that absorbs light and can increase the energy state of the material to facilitate reactions.
The results, which were published in the Journal of the American Chemical Society, offer a possible new tool to fight greenhouse gas emissions and climate change, said Stylianou, who studies crystalline, porous materials known as metal-organic frameworks, or MOFs.
MOFs are composed of positively charged metal ions coordinated to organic linker molecules and feature nanosized pores and tunable structural properties.
They can be designed with different components to figure out the properties of the MOF, and there are millions of possible MOFs, said Stylianou.
Chemistry researchers have made about 100,000 of them, and they have predicted the features of another half-million.
For this work, the researchers utilized a MOF, BVR-19, that has a unique structural feature, a sulfide-to-sulfide bond that can transiently cleave when exposed to light, producing reactive sulfur species.
Stylianou said, “The organic component does the important work. Instead of relying primarily on the metal atoms, our material uses its sulfur-containing organic building blocks to capture light energy and move electrons where they are needed to produce hydrogen. This represents a different way of thinking about how these materials should be designed.”
There’s no other expensive metal catalyst needed, he added, which could make it easier to design future light-driven hydrogen production systems. Another energy benefit of BVR-19 is that it is synthesized in aqueous solutions at room temperature and naturally.
Generating hydrogen by means of water splitting in a catalytic process is cleaner compared to producing hydrogen from natural gas in a carbon-dioxide-generating process called methane-steam reforming, said Stylianou.
Today, electrocatalysis, which involves passing an electric current through the catalyst, is employed in catalytic processes to generate hydrogen from water. The sustainability of electrocatalysis is based on the use of renewable energy, and the energy has to be cheap for market competitiveness.
The cost of producing hydrogen via methane-steam reforming is currently around $1.50 per kilogram, versus $5 per kilogram for green hydrogen.
Said Stylianou, who directs OSU’s Materials Discovery Laboratory, also known as the MaD Lab, “Our work provides a blueprint for designing better materials that can bring down the cost of green hydrogen,” said Stylianou, who directs OSU’s Materials Discovery Laboratory, known as the MaD Lab. By changing the metal while keeping the rest of the material essentially the same, we discovered why some versions of the MOF work much better than others. These findings provide new design rules for creating more effective materials for solar fuel production.”