A new family of materials that use light to make hydrogen from water has been developed by Oregon State University researchers, leading to new ways of transforming the sun’s rays into clean energy.
A collaboration led by Kyriakos Stylianou of the OSU College of Science has developed a photocatalyst that can be used to produce hydrogen at high speed and efficiency. Hydrogen is used in fuel cells for cars and in manufacturing many chemicals, including ammonia, in refining metals, and in making plastics.
A catalyst is a substance 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 findings, reported in the Journal of the American Chemical Society, offer a potential 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 determine 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 properties 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 important work is done by the organic part. Instead, our material uses its sulfur-containing organic building blocks to capture sunlight and move electrons where they are needed to produce hydrogen, rather than relying primarily on the metal atoms. This is a different way of thinking about how you should design these materials.”
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 synthesised in aqueous solutions at room temperature and spontaneously.
Generating hydrogen through water splitting in a catalytic process is cleaner than 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.
Stylianou, who directs OSU’s Materials Discovery Laboratory, known as the MaD Lab, says that “Our work provides a blueprint for designing better materials that can lower the cost of green hydrogen. By changing the metal but generally leaving the other components of the material unchanged, we learned why some versions of the MOF work much better than others. The findings provide new design rules for developing more effective materials for the production of solar fuels.”
The study was supported by the Murdock Charitable Trust, the National Science Foundation, and OSU College of Science.