Researchers Split Water to Create Renewable Energy
Engineering360 News Desk | September 10, 2015A research team at the Rice University has developed a solar-based water-splitting technology that uses light-activated gold nanoparticles to capture sunlight and transmit solar energy to high-excitation electrons, also known as hot electrons.
These electrons have the potential to drive useful chemical reactions, the researchers say. The challenge is that they decay rapidly and lose the ability to harness the energy, says Rice’s lead researcher Isabell Thomann. The hot electrons cool within a few trillionths of a second and their released energy is wasted heat.
However, if the hot electrons could be trapped before they had a chance to cool, providers of solar-energy could increase their solar-to-electric power-conversion efficiencies, potentially decreasing solar electricity costs.
During the research, light was captured by nanoparticles and converted into plasmons, which are electron waves flowing across the metal surface of the nanoparticles like fluid. While the plasmons exist at high-energy states for short durations, the team captured the energy and converted it into useful forms of heat or light energy.
The researchers developed a system to use the energy from hot electrons to split water molecules into oxygen and hydrogen. This is important because oxygen and hydrogen are raw materials for power supply in fuel cells. The researchers needed a way to separate hot electrons from corresponding “electron holes,” which are the low-energy states that the hot electrons move out of upon receiving a plasmonic jolt of energy. Driving the hot electrons beyond an energy threshold is the key. However, it is inefficient, they say.
Rice University researchers developed a way to capture energy from sunlight and convert it into renewable energy by splitting water molecules. Image Credit: Rice UniversityInstead, the team’s approach was a system that could carry away the electron holes, acting as a sieve or membrane. The holes pass through, but the electrons do not, alternately resting on the surface of the plasmonic nanoparticles. The system involves three layers. At the bottom is a sheet of shiny aluminium, in the middle is a thin coating of transparent nickel-oxide and on top is a configuration of plasmonic gold nanoparticles with a diameter of 10-30nm.
The disks receive sunlight directly or as a reflection from the aluminum layer and convert the incident light energy into hot electrons. The resulting electron holes are absorbed by aluminum and pass through the nickel oxide layer. The nickel oxide layer prohibits hot electrons from passing through; as a result they remain on the gold layer. Water is used to cover everything at this point and the gold nanoparticles are catalysts that aid in water molecule splitting.
The research team measured the value of photocurrent that was available for the splitting of water molecules instead of a direct measurement of oxygen and hydrogen gases that were produced due to water splitting.
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