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nano power!
Big Energy In Tiny Places

Counterintuitive as it may seem to try to solve big problems with tiny solutions, scientists are indeed looking for ways to address our current energy problems in nanoland.   Because nanotechnology exists in that sweet spot where Mother Nature hides her most bedazzling sleights of hand, it provides great promise as a place to discover new and better ways to energize the world.  Although researchers are taking vastly varied approaches to the application of this new science to an old problem, many cannot yet divulge the nature of their work, due to the constraints of intellectual property law.  But a review of some of the published work makes it clear that western Pennsylvania’s proud history of materials development and energy production is serving to foster the region’s metamorphosis into a hotbed nano-energy science and technology.


Nano Catalysts: Mother Nature’s Traffic Signals


Perhaps most promising of all nanotechnology’s promises is catalysis, the phenomenon by which a chemical reaction is altered by the presence of a substance, which ends up in the same condition at the end of the process as when it began.  Catalysts are molecules that jump into the middle of chemical reactions to redirect the paths the molecules would normally take to break apart and regroup by lowering or raising the energy it takes to get to their next chemical destination.  While catalysis is a complicated subject, thinking about it as nature’s system of roadways, bridges, tunnels, traffic lights and detour signs can help to untangle any mental traffic jams. Although catalysts come in millions of varieties and can be used to initiate, promote, accelerate, retard or inhibit reactions, they are most frequently used to accelerate them.  And since, as they say, time is money, accelerating a chemical process is almost always a good thing.


Nano-Catalysts for Clean Energy from Fossil Fuels

For decades, iron has been the catalyst of choice for turning solid fuels into liquid fuels.  In this two-step process, synthesis gas (syngas) is first produced by forcing high-pressure steam over coal or other hydrocarbon feedstocks to trigger the water-gas shift reaction in which hydrogen from the steam combines with carbon in the solid to yield a combustible gas.  In the second step the gas is put through a series of chemical processes, known as Fischer-Tropsch, which converts the gas to liquid.  The problem is that when operated for maximum output, the gasification/liquefaction process results in disproportionate quantities of carbon dioxide, the notorious perpetrator of global climate change.  Enter catalytic iron, which is renowned for its ability to accelerate the Fischer-Tropsch process without producing excess CO2.  In an attempt to make the most of iron's catalytic talents, at the National Energy Technology Laboratory, Dr. Christopher Matranga is investigating the nanoscale and angstrom-scale properties of iron (10 angstroms equal one nanometer).  He begins by making a gold substrate that self assembles so that its surface atoms form a zigzag pattern.  The gold surface is then exposed to iron vapor which, as it cools, forms cubic iron crystals on the gold where the zigs meet the zags.  Because the initial iron crystals, which are about one nanometer in size, are isolated at the “elbows” on the gold surface, they serve as ideal specimens for observation.  As more crystals form alongside and atop the original cubic crystals they begin to change shape, indicating that something is happening to their energy state.  Using some of the most advanced analytic techniques available today, Matranga measures the energy levels of the electron shells of the iron atoms that comprise the crystals that  he has so neatly isolated.   Armed with knowledge of the catalytic iron crystals’ physical structure and energy states, Matranga hopes to employ nanotechnology to address two pressing problems at once: to efficiently produce liquid fuel from solid feedstocks, such as coal and biomass, while at the same time reducing global carbon emissions.


Nano- Catalysts Extract the H from H20

In another example of using catalysts for fuel production, at Penn State University, Professor Thomas E. Mallouk and colleagues have begun to extract hydrogen, from its most abundant natural source and elusive hiding place - inside water molecules.  Mallouk’s catalytic dye-sensitized solar cells split water molecules into their constituent elements, hydrogen and oxygen, by using visible light to break the molecular bonds that hold them together.  The process is based on two principles of physics and chemistry:  1) light particles, or photons, can excite electrons orbiting around atomic nuclei to higher energy levels resulting in the production of a small electrical current, and; 2) an electrical current can break the molecular bonds that hold the hydrogen and oxygen atoms together in water.   Until recently, this could not be done with visible light because titanium dioxide (TiO2), the electrode material used in earlier experiments, absorbed only ultraviolet light, which represents only a tiny fraction of the sun’s energy.   Then recently, in a stroke of molecular virtuosity, the Mallouk group designed a photochemical cell with a nanocrystalline TiO2 semiconductor substrate sensitized to visible light by means of an orange dye.  The dye is composed of ruthenium-containing molecules attached to a small particle of iridium oxide.  Each molecule, which serves both to absorb visible light waves and to anchor itself at a critical distance from the titanium dioxide semiconductor film, measures between 1 and 5 nanometers in diameter.    When the titanium film and particles are immersed in water and exposed to visible light, the ruthenium-containing molecules absorb the light which increases their energy causing electrons to migrate to the titanium dioxide film.  As electrons migrate from the particles to the TiO2 the ensuing electrical current breaks the hydrogen-oxygen bonds in the water.    The result is gaseous streams of discrete hydrogen and oxygen molecules each containing two atoms of their respective elements.  While the system is not yet efficient enough to be considered for commercialization, it is the first time water splitting has been accomplished with a molecule that absorbs visible light.  Professor Mallouk predicts that the system’s efficiency is likely to improve as advances in molecular structure and electrochemical tuning of the constituent materials are made.


Nano-Photosynthesis

Also at Penn State, Dr. John Golbeck is investigating ways of harnessing photosynthesis to produce hydrogen by engineering the inter-molecular distance and energy levels of light-sensitive molecules inside plant reaction centers, where photosynthesis begins.  His work centers on the fact that during photosynthesis plants use sunlight to excite electrons and create billions of tiny electrical charges.  During excitation, negatively charged electrons inside chlorophyll molecules jump away from their resident cavities momentarily, leaving behind positively charged holes, thereby producing a state of “charge separation.” At first glance, charge separation resembles the basic elements of electricity: a positive charge on one side, and a negative charge on the other.  But, because both the electrons and their corresponding holes are effectively trapped inside their home molecules, they tend to recombine in short order, leaving too little time to do anything productive.  In response to that problem, Golbeck and colleagues have found a way to extend the charge separation time by coaxing excited electrons to jump out of their home molecules to more distant ones.


However, billions of charge-separated electrons and holes do not necessarily result in an electrical current.  “Unfortunately we don’t have a way of wiring photosystems to extract the electrical energy they generate,” Golbeck said.  “As an alternative, we are coaxing the photosynthetic reaction center into doing catalysis, to produce hydrogen from water.”  Golbeck has proven this concept by attaching platinum nanoparticles to photosynthetic reaction centers with molecular wires, which carry electrons to the platinum, thereby spitting hydrogen from water along the way.


Nano Fire

Working the energy problem from a completely different angle, at the University of Pittsburgh, Professor Gotz Veser is using nanotechnology to get clean energy out of fossil fuels by means of a new, green process called chemical looping combustion (CLC).  Veser is developing robust materials that allow the combustion process to be split into its component reactive parts, oxidation and reduction (redox reactions).  In contrast to conventional combustion, where fuel and air molecules undergo a series of continuous and almost instantaneous redox reactions at the combustion site, with CLC oxidation and reduction each take place in separate reactors.  First, in the oxidation reactor, oxygen is molecularly combined with a metal by exposing it to heated air, resulting in a metal oxide.  Next, the metal oxide is transferred to the reduction reactor where the oxygen riding on the metal reacts with a gaseous fuel, such as syngas, thereby generating heat as the metal is reduced to its original non-oxidized state. The flameless process yields the same amount of heat as that produced under conventional combustion. In addition, nitrogen, which comprises almost eighty percent of atmospheric air and is responsible for air-polluting nitrous oxides (NOx), is naturally excluded from the process because the oxidation takes place at temperatures too low to form them. Because reduction is limited to reactions between the oxide-borne oxygen and the fuel gas, the process yields a waste stream of carbon dioxide and steam. When the steam is condensed into liquid water, the remaining gas is almost pure carbon dioxide, which effectively eliminates the substantial cost of separating the CO2 by other means.  As good as CLC looks on paper, the tendency of metal particles to clump together (agglomerate) when heated presents a practical problem.  Veser's technology resolves the agglomeration problem by synthesizing the metal-oxide carriers as 10 nanometer nickel particles embedded in a ceramic matrix.  The novel, non-agglomerating material improves the performance and prolongs the life of the metal oxygen carriers.  At the same time it shortens the metal oxidation cycle time from as much as one hour for previous materials to less than one minute with Veser’s new one.


Friction-Reducing Nano Flowers

Taking an even less obvious tack, also at the University of Pittsburgh, Dr. Di Gao and colleagues are using nanotechnology to achieve transportation energy efficiency.  Inspired by the nanoscale structure of the water-repellent lotus leaf, Gao has developed a nano-structured paint that reduces drag at liquid/solid interfaces, such as pipe linings and ship hulls.  His work centers on the fact that some materials are attracted to water and some are repelled by it.  In laboratory jargon, the principles are known as hydrophilicity (attraction) and hydrophobicity (repulsion).  While both types of materials are quite common and very well understood, developing a coating that sticks to solids on one side at the same time it repels liquids on the other has been a challenge.  Gao has solved the problem by suspending nanoscale particles of a common form of iron, called hematite, inside a carbon fluoride liquid.  Once applied, the liquid adheres to the solid surface to cure, while the hematite particles migrate toward the outside, where they self- assemble into a hierarchical system of nanoscale platelets that aggregate into flower-like stalks and petals which, in contradiction of their innate tendency, repel water, rather than attract it.  When viewed under a microscope, most of liquid surface is essentially stood away from the solid surface, resulting in less liquid/solid contact, hence lower drag, which in turn means less energy to move a ship through an ocean or a liquid through a pipeline.  Early market studies done in anticipation of commercialization indicate potential world energy savings in the billions of dollars.


Nano for Solar Energy

Although sunlight is arguably our most abundant and practically limitless energy source, harvesting its electrical energy has proved steadfastly elusive and stubbornly expensive.   In response, Plextronics has developed a  technology that centers on the molecular self assembly of organic (non-metallic) nanowires that, depending on their chemical formulation and molecular structure, are able to absorb light and transform it into an electrical current or, alternatively, to convert an electrical current into visible light.    Known chemically as regio-regular polythiophenes, the secret to Plextronics’ technology was developed by Dr. Richard McCullough, now dean and vice president of research at Carnegie Mellon University, who figured out how to synthesize linear molecules with sulfur heads and tails at each end of a carbon chain that self-assemble into nanowires that conduct electricity.  Contaminants, called dopants, are mixed into the basic formula to tune the material’s optical and electromagnetic properties.   In the case of absorption of solar light, the materials are tuned to trap the electrons long enough to move along the conductive polymer nanowires, thereby generating an electrical current.  In the case of emission, or producing light, the process is reversed.  Plextronics’ nanowires are embodied in electro-conductive inks that can be printed as wires just the way a line like this ______ is printed on this page.  The technology holds the promise of leading to a new generation of energy efficient lighting.


Nano Optimizes Solar Panels

But not all nano-energy technology resides on the bleeding edge of science.  Twenty-odd years ago, Scott Rickert transformed the eyeglass business when he developed a scratch resistant nanofilm coating for Lenscrafters’ plastic eyeglass lenses.  Today Rickert is CEO of Cleveland-based Nanofilm, Inc. where he is in the process of developing a related product - a proprietary a self-cleaning film for solar photovoltaic electric cells, which he expects to improve efficiency by as much as fifty percent by reducing the amount of light-obscuring contaminants that typically accumulate on solar cell surfaces.  Rickert, a former professor of polymer physics, has evolved into a market pragmatist who eschews both scientific discovery and its attendant patents.  “One of our hallmarks is to never invent a solution, but to dramatically improve existing solutions,” he said. “Around the world, there are millions of installed solar panels operating at a practical efficiency of about fifteen percent, but their theoretical efficiency is twenty-five percent.  That ten percent difference represents a huge market opportunity for us. We think our films alone can have a dramatic impact on solar cell efficiency as well as the reduction of energy loss through windows.”


Nano Lightweighting for Wind Energy

While the bulk of nano energy activity happens in research laboratories, Bayer MaterialScience is seizing practical opportunities to produce nano-materials for the emerging alternative energy marketplace.  Bayer manufactures multi-walled carbon nanotubes for incorporation into polymers such as engineering resins, fiberglass, epoxies and composite materials, some of which are the material of choice for wind turbine blades.  As wind turbines grow larger, the ratio of blade stiffness to weight presents an increasingly difficult problem.  BayTubes, as they are called, are manufactured under a proprietary method called catalytic chemical vapor deposition (CCVD). They are produced and sold as granules composed of billions of multi-walled nanotubes, each one made up of 5 to 15 sleeves nested inside each other.  Each nanotube measures between 10 and 15 nanometers across and 100 to 1,000 nanometers long.  In order to achieve maximum effectiveness the tubes must be chemically functionalized to bind with their polymer matrix.  Once functionalized they are dispersed within the polymer and cast into pellets to be melted and vacuum-formed to the desired shape.  While components made of epoxy resin reinforced with carbon nanotubes are about as strong as aluminum and as stiff as fiberboard, they are typically 7,000 times lighter than steel.


Dollars for Nano Energy

In response to the opportunities associated with nanotechnology and the emerging energy economy, Dr. Alan Brown, Executive Director of the Pennsylvania Nanomaterials Commercialization Center has launched a new grant program designed to apply Pennsylvania’s historic strength in materials innovation to energy solutions. “The best solutions will come from marrying advanced energy materials research with nano-enabled energy products,” Brown said.
 
Based on current levels of activity, it looks as though shining light on the tiniest things we are able to detect may be the ideal way to illuminate Pittsburgh’s nano-energy future.


This article first appeared as a TEQ cover story.

©Copyright 2009 Thomas P. Imerito/ dba Science Communications



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©2009 Science Communications
thomas@science-communications.com