Renewable Energy: Splitting Water Molecules from Sunlight

Researchers from Rice University have a new way of harvesting sunlight for energy, and it involves using light-activated gold nanoparticles. These absorb the light and transfer energy to excited electrons known as "hot electrons." Essentially, they have to capture the high-energy electrons before they cool.

"Hot electrons have the potential to drive very useful chemical reactions, but they decay very rapidly, and people have struggled to harness their energy," Isabell Thomann, lead researcher and assistant professor at Rice, said in a news release. "For example, most of the energy losses in today's best photovoltaic solar panels are the result of hot electrons that cool within a few trillionths of a second and release their energy as wasted heat." 

According to the release, when the sunlight is captured, it is converted into plasmons, or waves of electrons that flow like a fluid across the metal surface of the nanoparticles.The researchers first had to find a way to separate the hot electrons from their corresponding "electron holes," or low-energy states. To do this, the team developed their own three-layered model. 

"Because of the inherent inefficiencies, we wanted to find a new approach to the problem," Thomann said in the release. "We took an unconventional approach: Rather than driving off the hot electrons, we designed a system to carry away the electron holes. In effect, our setup acts like a sieve or a membrane. The holes can pass through, but the hot electrons cannot, so they are left available on the surface of the plasmonic nanoparticles."

The scientists found a way to create a barrier so that hot electrons stay on the gold nanoparticles. Then they found that by laying the sheet of material flat and covering it with water, they could induce the gold nanoparticles to act as catalysts for water splitting. 

"Utilizing hot electron solar water-splitting technologies we measured photocurrent efficiencies that were on par with considerably more complicated structures that also use more expensive components," Thomann said. "We are confident that we can optimize our system to significantly improve upon the results we have already seen."

Their findings were recently published in the the American Chemical Society journal Nano Letters. 

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