Portable Tech Might Provide Drinking Water, Power to Villages

ScienceDaily (May 4, 2011) — Researchers have developed an aluminum alloy that could be used in a new type of mobile technology to convert non-potable water into drinking water while also extracting hydrogen to generate electricity.

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Such a technology might be used to provide power and drinking water to villages and also for military operations, said Jerry Woodall, a Purdue University distinguished professor of electrical and computer engineering.
The alloy contains aluminum, gallium, indium and tin. Immersing the alloy in freshwater or saltwater causes a spontaneous reaction, splitting the water into hydrogen and oxygen molecules. The hydrogen could then be fed to a fuel cell to generate electricity, producing water in the form of steam as a byproduct, he said.
"The steam would kill any bacteria contained in the water, and then it would condense to purified water," Woodall said. "So, you are converting undrinkable water to drinking water."
Because the technology works with saltwater, it might have marine applications, such as powering boats and robotic underwater vehicles. The technology also might be used to desalinate water, said Woodall, who is working with doctoral student Go Choi.
A patent on the design is pending.
Woodall envisions a new portable technology for regions that aren't connected to a power grid, such as villages in Africa and other remote areas.
"There is a big need for this sort of technology in places lacking connectivity to a power grid and where potable water is in short supply," he said. "Because aluminum is a low-cost, non-hazardous metal that is the third-most abundant metal on Earth, this technology promises to enable a global-scale potable water and power technology, especially for off-grid and remote locations."
The potable water could be produced for about $1 per gallon, and electricity could be generated for about 35 cents per kilowatt hour of energy.
"There is no other technology to compare it against, economically, but it's obvious that 34 cents per kilowatt hour is cheap compared to building a power plant and installing power lines, especially in remote areas," Woodall said.
The unit, including the alloy, the reactor and fuel cell might weigh less than 100 pounds.
"You could drop the alloy, a small reaction vessel and a fuel cell into a remote area via parachute," Woodall said. "Then the reactor could be assembled along with the fuel cell. The polluted water or the seawater would be added to the reactor and the reaction converts the aluminum and water into aluminum hydroxide, heat and hydrogen gas on demand."
The aluminum hydroxide waste is non-toxic and could be disposed of in a landfill.
The researchers have a design but haven't built a prototype.

Pairing Quantum Dots With Fullerenes for Nanoscale Photovoltaics

ScienceDaily (May 10, 2011) — In a step toward engineering ever-smaller electronic devices, scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory have assembled nanoscale pairings of particles that show promise as miniaturized power sources. Composed of light-absorbing, colloidal quantum dots linked to carbon-based fullerene nanoparticles, these tiny two-particle systems can convert light to electricity in a precisely controlled way.

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"This is the first demonstration of a hybrid inorganic/organic, dimeric (two-particle) material that acts as an electron donor-bridge-acceptor system for converting light to electrical current," said Brookhaven physical chemist Mircea Cotlet, lead author of a paper describing the dimers and their assembly method in Angewandte Chemie.
By varying the length of the linker molecules and the size of the quantum dots, the scientists can control the rate and the magnitude of fluctuations in light-induced electron transfer at the level of the individual dimer. "This control makes these dimers promising power-generating units for molecular electronics or more efficient photovoltaic solar cells," said Cotlet, who conducted this research with materials scientist Zhihua Xu at Brookhaven's Center for Functional Nanomaterials (CFN).
Scientists seeking to develop molecular electronics have been very interested in organic donor-bridge-acceptor systems because they have a wide range of charge transport mechanisms and because their charge-transfer properties can be controlled by varying their chemistry. Recently, quantum dots have been combined with electron-accepting materials such as dyes, fullerenes, and titanium oxide to produce dye-sensitized and hybrid solar cells in the hope that the light-absorbing and size-dependent emission properties of quantum dots would boost the efficiency of such devices. But so far, the power conversion rates of these systems have remained quite low.
"Efforts to understand the processes involved so as to engineer improved systems have generally looked at averaged behavior in blended or layer-by-layer structures rather than the response of individual, well-controlled hybrid donor-acceptor architectures," said Xu.
The precision fabrication method developed by the Brookhaven scientists allows them to carefully control particle size and interparticle distance so they can explore conditions for light-induced electron transfer between individual quantum dots and electron-accepting fullerenes at the single molecule level.
The entire assembly process takes place on a surface and in a stepwise fashion to limit the interactions of the components (particles), which could otherwise combine in a number of ways if assembled by solution-based methods. This surface-based assembly also achieves controlled, one-to-one nanoparticle pairing.
To identify the optimal architectural arrangement for the particles, the scientists strategically varied the size of the quantum dots -- which absorb and emit light at different frequencies according to their size -- and the length of the bridge molecules connecting the nanoparticles. For each arrangement, they measured the electron transfer rate using single molecule spectroscopy.
"This method removes ensemble averaging and reveals a system's heterogeneity -- for example fluctuating electron transfer rates -- which is something that conventional spectroscopic methods cannot always do," Cotlet said.
The scientists found that reducing quantum dot size and the length of the linker molecules led to enhancements in the electron transfer rate and suppression of electron transfer fluctuations.
"This suppression of electron transfer fluctuation in dimers with smaller quantum dot size leads to a stable charge generation rate, which can have a positive impact on the application of these dimers in molecular electronics, including potentially in miniature and large-area photovoltaics," Cotlet said.
"Studying the charge separation and recombination processes in these simplified and well-controlled dimer structures helps us to understand the more complicated photon-to-electron conversion processes in large-area solar cells, and eventually improve their photovoltaic efficiency," Xu added.
A U.S. patent application is pending on the method and the materials resulting from using the technique, and the technology is available for licensing. This work was funded by the DOE Office of Science.