Scientists at the Oregon State University in the U.S. have developed a new class of materials that uses a sulfur-based chemistry to make clean green hydrogen from water using only sunlight. This removes the need for expensive metal-based catalysts, paving the way for lower-cost green hydrogen production in the near future.
As the world looks to move away from fossil fuels through the use of solar and wind energy, the shortcomings of the latter are also coming to the fore. While large renewable energy plants are being run in various parts of the world, energy generated through wind and solar energy cannot be used to drive high-power applications.
Hydrogen, on the other hand, offers a cleaner way to run high-power applications, since its combustion produces water as a by-product and no carbon emissions. However, conventional hydrogen production relies on methane, which releases carbon into the atmosphere. So, scientists have been looking for greener methods to produce hydrogen.
Photocatalysis of water
The simplest way to produce hydrogen is it split water using electricity. This process can be green, depending on how the electricity is sourced. Electricity generated at wind and solar power plants is now widely available, but the cost of hydrogen generated this way is around $5 per kilogram.
Photocatalysis is a much more direct approach, as it uses a material in its high-energy state activated by sunlight to bring about the same reaction and at a faster rate. Typically, photocatalysts are materials called Metal-Organic Frameworks (MOFs), which are crystalline, porous materials.
Scientists often leverage the pores and structures and fine-tune them to attain different properties in these materials for different applications. At the center of the MOF are positively charged metal ions connected by organic linker molecules. The Oregon team worked with a MOF called BVR-19 that helped generate green hydrogen more easily than other MOFs.
What makes BVR-19 special?
BVR-19 contains a sulfur-sulfur bond that breaks when exposed to sunlight and creates highly reactive sulfur species. While the metal in the MOF works as the catalyst, in photoactivated BVR-19, the sulfur-containing organic blocks capture the light and move electrons to produce hydrogen.
This means that BVR-19 does not need an expensive metal catalyst to generate green hydrogen, thereby reducing production costs. An added advantage of the material is that it BVR-19 can be made easily at room temperature, reducing costs of its own production too, a plus when the technology has to be scaled.
“Our work provides a blueprint for designing better materials that can bring down the cost of green hydrogen,” said Kyriakos Stylianou, a professor at the Oregon State University and director of its Materials Discovery Laboratory, where this research was done, in a press release.
“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.”
The research findings were published in the Journal of the American Chemical Society.
