Researchers at Oregon State University have created a new class of materials that can use light to produce hydrogen from water, offering a potentially cleaner way to convert solar energy into fuel. The work was led by Kyriakos Stylianou of the OSU College of Science. His team developed a photocatalyst capable of producing hydrogen quickly and efficiently. Hydrogen is widely used in vehicle fuel cells, as well as in ammonia production, metal refining and plastics manufacturing. Using light to speed up chemical reactions A catalyst is a substance that speeds up a chemical reaction without undergoing permanent changes to the process, Stylianou said. A photocatalyst works in a similar way but is activated by light. After absorbing light, the material reaches a higher energy state and can use that energy to drive chemical reactions more quickly. The findings, published in the Journal of the American Chemical Society, could provide researchers with another tool to reduce greenhouse gas emissions and address climate change, Stylianou said. His research focuses on metal-organic frameworks, or MOFs, which are porous, crystalline materials with structures that can be carefully customized. MOFs are built from positively charged metal ions surrounded by organic “linker” molecules. Its small pores and adjustable structures allow scientists to tune its properties for different applications. Millions of different MOF structures are theoretically possible, Stylianou said. Chemistry researchers have already synthesized almost 100,000 of them, while the properties of about half a million others have been predicted. An unusual sulfur bond drives the reaction For this study, the researchers focused on a MOF called BVR-19. The material contains an unusual sulfide-to-sulfide bond that temporarily breaks when exposed to light, producing highly reactive sulfur species. “The organic component does the important work,” Stylianou said. “Rather than relying primarily on metal atoms, our material uses its sulfur-containing organic components 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.” That approach means BVR-19 does not require an additional expensive metal catalyst, Stylianou added. This could simplify the design of future light-powered hydrogen production systems. The material also has another potential advantage. BVR-19 forms spontaneously in aqueous solutions at room temperature, reducing the amount of energy needed to produce it. A cleaner alternative to conventional hydrogen Producing hydrogen by splitting water with a catalyst can be cleaner than the dominant industrial method, which relies on natural gas. That conventional process, known as methane steam reforming, releases carbon dioxide while producing hydrogen. Existing methods for producing hydrogen from water often rely on electrocatalysis, which uses electricity to drive the catalytic reaction. The environmental benefits of that approach depend largely on the source of the electricity. To remain sustainable and economically competitive, energy must come from low-cost renewable sources. Currently, hydrogen produced by methane steam reforming costs about $1.50 per kilogram, while green hydrogen costs about $5 per kilogram. New design rules for cheaper green hydrogen “Our work provides a model for designing better materials that can reduce 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 efficient materials for solar fuel production.” MaD Lab members Emmanuel Musa, Dylan Pyle, Jacob Lessard, Andrzej Gladysiak, Ankit Yadav, Silas Blessed and Prayash Mohanty were joined in the research by Oregon State’s Logan Lancaster, Taylor Krueger, Min Soo Jung, Galen Fritz, Jacob Hirschi, Hongliang Huang, William Stickle, Xiulei “David” Ji, Chong Fang and Tim Zuehlsdorff. The Murdock Charitable Trust, the National Science Foundation and the OSU College of Science supported the study.
