Thursday, October 13, 2011

#ENERGY: "Artificial Leaf Turns Water Into Fuel"

As free as a water lily floating on a lake, solar-panels coated with a new catalytic material can harvest hydrogen fuel from ordinary water with no wires attached.

Many energy researchers have proposed using solar cells to generate electricity for electrolysis that splits water into its component parts--hydrogen and oxygen--which can then be used to power fuel cells. However, Massachusetts Institute of Technology (MIT) has combined all those functions into a single free-standing unit, which generates fuel whenever it is submerged in water illuminated by the sun.
Plants generate their own fuel for metabolism by harvesting sunlight, making MIT's new invention something like an artificial water-lily leaf. The true novelty of the device, however, is that it is free standing--a simple single panel with no connection wires to anything outside itself, and yet when submerged in water it immediately starts generating fuel from sunlight.

A flat panel module generates electricity with no wires attached, by virtue of built-in solar cells that split water into hydrogen fuel and oxygen. (Source: MIT)
The key to its novel behavior is the catalytic material used to coat each side of the free-standing solar panel. Rather than using rare expensive catalysts like platinum, the team of MIT professor Daniel Nocera used only Earth-abundant materials. On the front-side of the silicon solar panel is a layer of cobalt catalyst, which was discovered by Nocera a few years ago, and which was subsequently licensed to Sun Catalytix, which Nocera founded to commercialize the technology. Sun Catalytix chemist Steven Reece, Nocera's former graduate student, helped adapt the cobalt catalyst to the oxygen producing side of this new artificial leaf application of silicon solar cells, along with a team of five other researchers from Sun Catalytix and MIT.
The other side of the artificial leaf is coated with a nickel-molybdenum-zinc alloy, which splits off hydrogen from the water molecules. Systems using the technique will work by constructing a water tank with two chambers separated by the two-sided solar panels. Hydrogen can then be collected from one side while oxygen is collected from the opposite side. Each gas can then be stored separately, and later used to power a fuel cell which recombines them to generate electricity on demand, or could even be burned in an internal combustion engine to directly produce work.
Next, the researchers want to increase the efficiency of their artificial leaf, which is only about 2.5 percent efficient. The team is also trying out solar cells made from less expensive materials than crystalline silicon, such as thin films of iron oxide, potentially lowering the price of finished systems.
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