By Dan Newman University of Michigan
A new, stable artificial photosynthesis device doubles the efficiency of harnessing sunlight to break apart both fresh and salt water, generating hydrogen that can then be used in fuel cells. The device could also be reconfigured to turn carbon dioxide back into fuel.
Hydrogen is the cleanest-burning fuel, with water as its only emission. But hydrogen production is not always environmentally friendly. Conventional methods require natural gas or electrical power. The method advanced by the new device, called direct solar water splitting, only uses water and light from the sun.
“If we can directly store solar energy as a chemical fuel, like what nature does with photosynthesis, we could solve a fundamental challenge of renewable energy,” said Zetian Mi, a professor of electrical and computer engineering at the University of Michigan who led the research while at McGill University in Montreal.
Faqrul Alam Chowdhury, a doctoral student in electrical and computer engineering at McGill, said the problem with solar cells is that they cannot store electricity without batteries, which have a high overall cost and limited life.
The colorized electron microscope image shows the gallium nitride towers of the artificial photosynthesis device at 25k magnification. These nanostructures rip water molecules apart into hydrogen and oxygen to produce clean hydrogen fuel.
Image credit: Faqrul A. Chowdhury, McGill University
Image credit: Faqrul A. Chowdhury, McGill University“
“Although the 3 percent efficiency might seem low, when put in the context of the 40 years of research on this process, it’s actually a big breakthrough,” Mi said. “Natural photosynthesis, depending how you calculate it, has an efficiency of about 0.6 percent.”
He adds that 5 percent efficiency is the threshold for commercialization, but his team is aiming for 20 or 30 percent efficiency.
Mi conducts similar research to strip carbon dioxide of its oxygen to turn the resulting carbon into hydrocarbons, such as methanol and syngas. This research path could potentially remove carbon dioxide from the atmosphere, like plants do.
“That’s the truly exciting part,” Mi said.
The device is documented in the study, “A photochemical diode artificial photosynthesis system for unassisted high efficiency overall pure water splitting,” published in Nature Communications. Along with Mi and Chowdhury, co-authors include Michel Trudeau of the Center of Excellence in Transportation Electrification and Energy Storage, Hydro-Québec, and Hong Guo of McGill University.
The work was supported by the Fuel Cell Technologies Office of the U.S. Department of Energy and Emissions Reduction Alberta.
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