Sunday, May 22, 2011

#ENERGY: "Smarter Hydrogen Fuel Maker Mimics Plants"

The emerging hydrogen economy depends on finding smarter ways to generate the volatile gas from plentiful natural resources, such as splitting water into hydrogen and oxygen with sunlight. Smarter hydrogen generators will ditch precious metals for fields of silicon nanopillars etched with semiconductor fabrication equipment, thus realizing the dream of cheap, abundant hydrogen fuel generated from water and sunlight a la plants.

Silicon nanopillars—each 2 microns in diameter—etched with semiconductor fabrication equipment substitute for expensive platinum electrodes, enabling cheap hydrogen generation from water and sunlight. (Source: Technical University of Denmark)

According to the Department of Energy (DoE) we should be mimicking the way plants generate their own fuel from water and sunlight, but unfortunately the price of convention electrolysis is too high due to its use of expensive platinum catalysts. To realize the dream, DoE-funded researchers are now fabricating tiny micrometer-sized pillars of cheap abundant silicon to take the place of expensive platinum catalysts, thus promising to bring down the price of hydrogen fuel and enabling widespread commercialization.

Plants use photosynthesis to produce a fuel (adenosine triphosphate) from sunlight and water, which is then stored until it is needed for respiration, growth and other normal cellular operations. The "hydrogen economy" concept mimics this operation by using sunlight to drive an artificial photosynthesis-like action more accurately termed photo-electro-chemical (PEC) water splitting.

The result could be abundant, cheap hydrogen gas that can be stored indefinitely without the need for batteries, then converted into energy on-the-fly either by burning it directly in engines or using it to produce electricity in fuel cells.
Today most hydrogen fuel is produced from natural gas, which unfortunately releases carbon dioxide as a by-product. However, if artificial photosynthesis can be perfected, then hydrogen fuel could be produced from nothing more than water and sunlight, making it cleaner and cheaper than any conventional fuel.

Unfortunately, the easiest way to split water into hydrogen and oxygen makes use of expensive platinum catalysts, but now the SLAC (originally Stanford Linear Accelerator Center) National Accelerator Laboratory, working with Stanford University and the Technical University of Denmark, believes it has eliminated the need for expensive catalysts, in favor of microscopic fields of pillars etched in silicon.

The key to the researchers' hydrogen generation method was their discovery that depositing nanoscale clusters of the molybdenum-sulfide molecules onto its fields of silicon pillars enabled them to split the hydrogen off of the oxygen in H2O (water) when exposed to sunlight. The resulting "chemical solar cell" was found to work as well as more expensive conventional designs using expensive platinum catalysts.

Now the researchers are working on a mechanism that separates the hydrogen from the oxygen generated, thus allowing each to be separately stored until needed as fuel for combustion or to produce electricity in a fuel cell.

Jens Nørskov at the DoE's SLAC National Accelerator Laboratory worked on the project with researchers at Stanford University and a team at the Technical University of Denmark led by Ib Chorkendorff and Søren Dahl.
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