Researchers at the University of California – Santa Barbara are pretty excited over this new solar cell they’ve been working on, and who can blame them? For the past 100 years or so, everybody’s been tinkering around with solar energy conversion based on semiconductors and meanwhile a promising new field called plasmonics has been bubbling up under the surface. The research team has developed a free-floating plasmonic device that produces hydrogen from water using only clean, renewable solar energy, which could lead to high efficiency, low cost hydrogen production for fuel cell electric vehicles, among other uses.
Low Cost Hydrogen for Fuel Cells
Before we get into the details of the new device, let’s take a look at how it could fit into the big picture, sustainably speaking. Zero emission hydrogen fuel cells have a promising future, but there is one big catch: they run on hydrogen, and splitting water into hydrogen and oxygen is an expensive, energy-intensive process.
One way to get around that is to use solar energy to power the process, such as the “artificial leaf” solar cell developed at MIT.
Plasmonic devices offer a more durable, and potentially more efficient, way to accomplish the same goal.
The UC-Santa Barbara Plasmonic Solar Cell
As described by UCSB writer Sonia Fernandez, when sunlight strikes a conventional solar cell made of semiconductor material, electrons shift positions to leave positively charged “holes,” which creates an electric current.
Plasmonic solar devices also create a shift in electron position using solar energy, but they are made of metal nanostructures instead of semiconductors.
The UCSB team created a cell in the form of a “‘forest’ of gold nanorods,” topped off with titanium dioxide crystals and platinum nanoparticles. When placed in water with a catalyst and exposed to visible light, electrons in the nanorods oscillate together, creating a phenomenon called plasmonic waves. Fernandez writes:
“As the ‘hot’ electrons in these plasmonic waves are excited by light particles, some travel up the nanorod, through a filter layer of crystalline titanium dioxide, and are captured by platinum particles. This causes the reaction that splits hydrogen ions from the bond that forms water. Meanwhile, the holes left behind by the excited electrons head toward the cobalt-based catalyst on the lower part of the rod to form oxygen.”
As a replacement for semiconductor-based solar cells, the plasmonic cell is still years away from commercial development. However, one promising aspect of the work so far is the ruggedness of the nanorods, which could lead to a device with a far longer lifespan than today’s conventional solar cells in addition to increased efficiency.
Get Ready for a Plasmonic Future
UCSB isn’t the only research institution dreaming of a plasmonic future. Over at Stanford University, researchers are working on “waffle iron” thin-film solar technology that integrates a plasmonic effect, resulting in a thinner, more efficient and more durable film.
Meanwhile, other paths to clean, low-cost hydrogen production are also in the works. Lawrence Berkeley National Laboratory, for example, is developing a solar-powered process that uses “disordered” titanium nanocrystals to boost efficiency, and Brookhaven National Laboratory is working on an inexpensive nickel-based catalyst.