Broad-spectrum solar breakthrough could efficiently produce hydrogen

A new molecule developed by Ohio State University scientists can harvest energy from the entire visible spectrum of light, bringing in up to 50 percent more solar energy than current solar cells, and can also catalyze that energy into hydrogen.

Hydrogen is viewed by many folks, particularly in Japan and Korea, as the clean-burning fuel that might power our vehicles in a low-emissions future. One way to produce hydrogen is to split it out of water. This is typically done by splitting water molecules into hydrogen and oxygen using electricity, but a potentially simpler and more efficient way to do it may be through photocatalytic water splitting, which uses light itself as the energy source instead of electricity, removing electricity production from the process altogether.

Nobody has yet managed to commercialize photocatalytic hydrogen production, but it's a hot area of research, and this OSU team claims it's discovered one of the most efficient photocatalytic molecules to date.

The molecule has shown a unique ability to use light from right across the visible spectrum. Where most previous photocatalysts have focused on high-energy ultraviolet wavelengths, this one can capture energy from ultraviolet, all the way through the visible spectrum and well into the near infrared range, meaning it can absorb up to 50 percent more solar energy than current solar cells.

Many previous attempts, the researchers say, have also lost efficiency due to their use of two or more molecules in the catalyst. Energy is lost in these systems as these molecules exchange electrons – not a problem with OSU's single-molecule solution.

The new photocatalyst in question is a form of the element rhodium. The researchers tested it in a lab by shining LED light onto an acid solution containing the active molecule, and found that hydrogen gas was released.

“What makes it work is that the system is able to put the molecule into an excited state, where it absorbs the photon and is able to store two electrons to make hydrogen,” says professor Claudia Turro, director of the OSU Center for Chemical and Biophysical Dynamics. “This storing of two electrons in a single molecule derived from two photons, and using them together to make hydrogen, is unprecedented.”

There are still problems to be worked out before this becomes a commercially viable means of producing clean fuel. The main one is that rhodium is rare and expensive; Turro says the team is trying to figure out how to build it from less expensive materials and make it last longer. But this research certainly gets photocatalytic hydrogen production one step closer to being a reality.

The research has been published in Nature Chemistry.

Source: Ohio State University