August R&D Round Up

E-mail Melanie Martella

This month we've got a raft of energy harvesting and storage breakthroughs, including improved efficiency for quantum dot solar cells, energy storage in a nanowire, and graphene used to harvest energy from flowing water.

Boosting Solar Cell Efficiency
One of the biggest drawbacks to using solar cells is their inefficiency; sure, the sun lashes us with a huge amount of energy, so it's not like we're dealing with a scarce resource, but researchers all over the world are busy trying to get a more efficient conversion from solar radiation into usable energy as well as figuring out how to make better and cheaper solar cells. Researchers at the University of Toronto's Dept. of Electrical and Computer Engineering, led by professor Edward H. Sargent, have been focusing on inexpensive solar cells that use semiconductor nanoparticles called colloidal quantum dots (CQDs) that the researchers can tune to absorb energy across the whole of the sun's spectrum. (For the skinny on how this works, I'd suggest visiting the Sargent group's photovoltaic research page.). By connecting a series of cells, each of which is tuned to a different portion of the spectrum, the researchers can boost the efficiency markedly but the problem was how to link the cells together. In a paper published in Nature they explain how they've managed to do just that. For a much fuller explanation of the research, I'd suggest reading the PhysOrg article, "Tiny tech, big results: Quantum dot solar cells increase solar conversion efficiency."

A Battery in a Nanowire
Is there no end to the clever things that are possible with nanowires? Clearly, the answer is no. As an illustration of this fact, I submit the recent work from Rice University, in which researchers have demonstrated a hybrid battery/supercapacitor that uses thousands of nanowires, each of which functions as a battery. The nanowire lithium ion batteries use a nickel-tin nanowire to act as the battery's anode, they're then coated inside and out with polyethylene oxide (PEO) which acts as the electrolyte and as a buffer between the nanowires, and then polyaniline (PANI) is drop-coated into the center of the tubes to act as the cathode. Llithium ions move through the electrolyte to the anode and then move on to the cathode, which stores the ions in bulk and acts as a supercapacitor. Craziness. To learn more, read "Rice builds nanowire battery."

Water Power Gets Smaller
The mighty Hoover Dam and New England's raft of water-powered mills now have a much, much, much smaller cousin: researchers at Renssellaer Polytechnic Institute have developed a nanoengineered graphene coating that can harvest energy from flowing water. Essentially, as water flows over the graphene coating, ions in the water interact with free charge carriers in the graphene surface and induce a voltage in the direction of the water flow. A very, very small voltage. When the researchers used a dilute hydrochloric acid solution flowing at 0.01 m/s, the 30 by 16 µm square of graphene film generated 85 nW. So, it's a pretty small voltage, but that's not too shabby. The researchers hope to develop the technology further to power small sensors whichwould be introduced into existing cracks and crevices in the earth to search for oil and gas deposits.


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