New material for lithium-ion storage - Graphdiyne

Researchers has devised new two-dimensional carbon based materials – called Graphydiyne.  

Carbon is the anode material in lithium-ion batteries. Its layered structure allows lithium ions to travel in and out of the spaces between layers during battery cycling. Carbon has a highly conductive two-dimensional hexagonal crystal lattice, and they form a stable, porous network for efficient electrolyte penetration. However, the fine-tuning of the structural and electrochemical properties is difficult as these carbon materials are mostly prepared from polymeric carbon matter in a top-down synthesis.

Graphdiyne being a hybrid two-dimensional network made of hexagonal carbon rings bridged by two acetylene units, has been used as a nanoweb membrane for the separation of isotopes. However, its distinct electronic properties and web-like structure also make graphdiyne suitable for electrochemical applications. Changshui Huang from the Chinese Academy of Sciences, Beijing, and colleagues have investigated the lithium-storage capabilities and electrochemical properties of tailor-made, electronically adjusted graphdiyne derivatives.

The scientists synthesized the graphdiyne derivatives in a bottom-up approach by adding precursors on a copper foil, which self-organized to form ordered layered nanostructures with distinct electrochemical and morphological properties.

Among these functional groups, those exerting electron-withdrawing effects reduced the band gap of graphdiyne and increased its conductivity, the authors reported. The cyano group was especially effective and, when used as an anodic material, the cyano-modified graphdiyne demonstrated excellent lithium-storage capacity and was stable for thousands of cycles, as the authors reported.

The authors conclude that modified graphdiyne can be prepared by a bottom-up strategy, which is also best suited to build functional two-dimensional carbon material architectures for batteries, capacitors, and other electrocatalytic devices.

 

Storage solution using silicon in battery with the aid of nanotechnology

Silicon along with carbon nanotubes has been used to develop a nanostructure to make an effective design for battery anodes. CNT is used to strengthen the material and modify the way the silicon interacts with lithium, which has been extensively used in electrical cars and other devices.

Scientists at the U.S. Department of Energy's Pacific Northwest National Laboratory have used a novel way to use silicon. Silicon, used in computer chips is attractive as it can hold 10 times the electrical charge per gram compared to graphite. The trouble is, silicon expands greatly when it encounters lithium, and it is too weak to withstand the pressure of electrode manufacturing.

To tackle these issues, a unique nanostructure that prevents silicon's expansion when it is mixed with carbon. Scientist work, which was recently published in the journal Nature Communications, could inform new electrode material designs for other types of batteries and eventually help increase the energy capacity of the lithium-ion batteries in electric cars, electronic devices, and other equipment.

How they do it!!

A conductive and stable form of carbon, graphite is well suited to packing lithium ions into a battery's anode as it charges. Silicon can take on more lithium than graphite, but it tends to expand about 300 percent in volume, causing the anode to break apart. The researchers created a porous form of silicon by aggregating small silicon particles into microspheres about 8 micrometers in diameter.

The electrode with porous silicon structure exhibits a change in thickness of less than 20 percent while accommodating twice the charge of a typical graphite anode. However, unlike previous versions of porous silicon, the microspheres also exhibited extraordinary mechanical strength, thanks to carbon nanotubes that make the spheres resemble balls of yarn.

The researchers created the structure sequentially, starting by coating the carbon nanotubes with silicon oxide. Next, the nanotubes were put into an emulsion of oil and water. Then they were heated to boiling. The coated carbon nanotubes condense into spheres when the water evaporates. Then aluminum and higher heat is used to convert the silicon oxide into silicon, followed by immersion in water and acid to remove by-products. What emerges from the process is a powder composed of the tiny silicon particles on the surface of carbon nanotubes.

New nanomaterial for longer battery life

An architecture nanostructured material has been recently developed by researchers at the University of California using nanocrystalline ruthenium oxide coupled with graphene. This technology could improve the quality of the supercapacitors leading to long lasting battery life in portable electronics.

 

The present study showed that two times more energy and power can be achieved with this material compared to commercial supercapacitors. The electrode and/or supercapacitors made with above mentioned nanomaterial can be cycled over 8000 times without any fatigue because of its high energy density. Nanostructured materials also rendered large surface area, high electrical conductivity, short ion diffusion pathways and excellent interfacial integrity, making these high energy supercapacitor electrodes ideal for future energy storage applications.

New material for fuel cell catalyst

Efficient, robust and economical catalyst materials hold the key to achieving a breakthrough in fuel cell technology. Scientists from Jülich and Berlin have developed a material for converting hydrogen and oxygen to water using a tenth of the typical amount of platinum that was previously required. With the aid of state-of-the-art electron microscopy, the researchers discovered that the function of the nanometre-scale catalyst particles is decisively determined by their geometric shape and atomic structure. This discovery opens up the opportunity for further improved catalysts for energy conversion and storage. 

Hydrogen-powered fuel cells are regarded as a clean alternative to conventional combustion engines, as the only substance produced during operation is water. At present, the implementation of hydrogen fuel cells is being hindered by the high material costs of platinum. Large quantities of the expensive noble metal are still required for the electrodes in the fuel cells at which the chemical conversion processes take place. Without the catalytic effect of the platinum, it is not currently possible to achieve the necessary conversion rates.

As catalysis takes place at the surface of the platinum only, material can be saved and, simultaneously, the efficiency of the electrodes improved by using platinum nanoparticles, thus increasing the ratio of platinum surface to material required. Although the tiny particles are around ten thousand times smaller than the diameter of a human hair, the surface area of a kilogram of such particles is huge.

However, more platinum can be saved by mixing it with nickel or copper. Scientist have succeeded in developing efficient metallic catalyst particles for converting hydrogen and oxygen to water using only a tenth of the typical amount of platinum that was previously required. 

The new catalyst consists of octrahedral-shaped nanoparticles of a platinum-nickel alloy. The researchers discovered that the unique manner in which the platinum and nickel atoms arrange themselves on the surfaces to accelerate the chemical reaction between hydrogen and oxygen to form water. Round or cubic particles have different atomic arrangements at the surface and are therefore less effective catalysts for the chemical reaction, which could be compensated by using increased amounts of noble metal.

“Antenna” like InP nanowires for high solar efficiency

In a recent study, researchers from Lund University in Sweden have shown how nanowires could pave the way for more efficient and cheaper solar cells. This finding first shows that it is possible to use nanowires to manufacture solar cells.

Research on solar cell nanowires is on the rise globally. Until now the unattained dream figure was ten per cent efficiency; but now scientists are able to report an efficiency of 13.8 per cent.

The nanowires are made of the semiconductor material indium phosphide and work like antennae that absorb sunlight and generate power. The nanowires are assembled on surfaces of one square millimetre which can hold four million nanowires. A nanowire solar cell can produce an effect per active surface unit several times greater than today's silicon cells.

Nanowire solar cells have not yet made it beyond the laboratory, but the plan is that the technology could be used in large solar power plants in sunny regions.

The Lund researchers have now managed to identify the ideal diameter of the nanowires and how to synthesize them.

The right size is essential for the nanowires to absorb as many photons as possible. If they are just a few tenths of a nanometre, their function is significantly impaired. The silicon solar cells that are used to supply electricity for domestic use are relatively cheap, but inefficient because they are only able to utilise a limited part of the effect of the sunlight. The reason is that one single material can only absorb part of the spectrum of the light.

Research carried out alongside that on nanowire technology therefore aims to combine different types of semiconductor materials to make efficient use of a broader part of the solar spectrum. The disadvantage of this is that they become extremely expensive and can therefore only be used in applications such as on satellites and military planes.

However, this is not the case with nanowires. Because of their small dimensions, the same sort of material combinations can be created with much less effort, which offers higher efficiency at a low cost. The process is also less complicated. In this study, the researchers have shown that the nanowires can generate power at the same level as a thin film of the same material, even if they only cover around 10 per cent of the surface rather than 100 per cent.

 

For further studies:

http://www.sciencemag.org/content/early/2013/01/16/science.1230969

Solar cell paint developed

Suppose if the next coat of paint you put on the outside of your home generates electricity from light -- electricity that can be used to power the appliances and equipment on the inside.

A team of researchers at the University of Notre Dame has made a major advance toward this vision by creating an inexpensive material that uses semiconducting nanoparticles to produce energy.

By incorporating power-producing nanoparticles, called quantum dots, into a spreadable compound, a one-coat solar paint was produced that can be applied to any conductive surface without special equipment.

The team's search for the new material, described in the journal ACS Nano, centered on nano-sized particles of titanium dioxide, which were coated with either cadmium sulfide or cadmium selenide. The particles were then suspended in a water-alcohol mixture to create a paste. When the paste was brushed onto a transparent conducting material and exposed to light, it created electricity.

The best light-to-energy conversion efficiency achieved by this is 1 percent, which is well behind the usual 10 to 15 percent efficiency of commercial silicon solar cells; but this paint can be made cheaply and in large quantities. If efficiency can be improved, it would be worthwhile to use in day-today activities.

Newest Energy Material: Application in Computer, Lighting Technologies

Arizona State University researchers have created a new compound crystal material that promises to help produce advances in a range of scientific and technological pursuits.

The newest material, called erbium chloride silicate, can be used to develop the next generations of computers, improve the capabilities of the internet, increase the efficiency of silicon-based photovoltaic cells to convert sunlight into electrical energy, and enhance the quality of solid-state lighting and sensor technology.

Ning's research team of team of students and post-doctoral degree assistants help synthesize the new compound in ASU's Nanophotonics Lab in the School of Electrical, Computer and Energy Engineering, one of the university's Ira A. Fulton Schools of Engineering.

The breakthrough involves the first-ever synthesis of a new erbium compound in the form of a single-crystal nanowire, which has superior properties compared to erbium compounds in other forms.

Erbium is one of the most important members of the rare earth family in the periodic table of chemical elements. It emits photons in the wavelength range of 1.5 micrometers, which are used in the optical fibers essential to high-quality performance of the Internet and telephones.

Erbium is used in doping optical fibers to amplify the signal of the internet and telephones in telecommunications systems. Doping is the term used to describe the process of inserting low concentrations of various elements into other substances as a way to alter the electrical or optical properties of the substances to produce desired results. The elements used in such processes are referred to as dopants.

With the new erbium compound, 1,000 times more erbium atoms are contained in the compound. This means many devices can be integrated into a chip-scale system. Thus the new compound materials containing erbium can be integrated with silicon to combine computing and communication functionalities on the same inexpensive silicon platform to increase the speed of computing and internet operation at the same time. Erbium materials can also be used to increase the energy-conversion efficiency of silicon solar cells.

Silicon does not absorb solar radiation with wavelengths longer than 1.1 microns, which results in waste of energy -- making solar cells less efficient. Erbium materials can remedy the situation by converting two or more photons carrying small amounts of energy into one photon that is carrying a larger amount of energy. The single, more powerful photon can then be absorbed by silicon, thus increasing the efficiency of solar cells.

Erbium materials also help absorb ultraviolet light from the sun and convert it into photons carrying small amounts of energy, which can then be more efficiently converted into electricity by silicon cells. This color-conversion function of turning ultraviolet light into other visible colors of light is also important in generating white light for solid-state lighting devices.

While erbium's importance is well-recognized, producing erbium materials of high quality has been challenging. The standard approach is to introduce erbium as a dopant into various host materials, such as silicon oxide, silicon, and many other crystals and glasses. One big problem has been that we have not been able to enough erbium atoms could not be introduced into crystals and glasses without degrading optical quality, because too many of these kinds of dopants would cluster, which lowers the optical quality.

What is unique about the new erbium material synthesized here is that erbium is no longer randomly introduced as a dopant. Instead, erbium is part of a uniform compound and the number of erbium atoms is a factor of 1,000 more than the maximum amount that can be introduced in other erbium-doped materials. Increasing the number of erbium atoms provides more optical activity to produce stronger lighting. It also enhances the conversion of different colors of light into white light to produce higher-quality solid-state lighting and enables solar cells to more efficiently convert sunlight in electrical energy. In addition, since erbium atoms are organized in a periodic array, they do not cluster in this new compound. The fact that the material has been produced in a high-quality single-crystal form makes the optical quality superior to the other doped materials.

This new erbium compound can be used for various applications, such as increasing silicon solar cell efficiency and making miniaturized optical amplifiers for chip-scale photonic systems for computers and high-speed internet.

Mass production of non-reflective polymer surfaces (nanofabrication) yields more efficiency in solar energy

A key hurdle in realizing high-efficiency, cost-effective solar energy technology is the low efficiency of current power cells. In order to achieve maximum efficiency when converting solar power into electricity, ideally there is a need for solar panel that can absorb nearly every single photon of light across the entire spectrum of sunlight and irrespective of the sun's position in the sky.

One way to achieve suppression of sunlight's reflection over a broad spectral range is by using nanotextured surfaces that form a graded transition of the refractive index from air to the substrate. Researchers in Finland have now demonstrated a scalable, high-throughput fabrication method for such non-reflecting nanostructured surfaces.

The main advances of this work are in the field of nanofabrication. It was published in a recent paper in Advanced Materials ("Non-Reflecting Silicon and Polymer Surfaces by Plasma Etching and Replication").

The process involves a maskless deep reactive ion etching process that produces nanospikes on a silicon wafer. The process is known as black silicon process. The geometry of the nanospikes i.e. height, width and also the density can be controlled by changing the etching parameters. The main strength of the maskless method is its high throughput.

Different applications require different types of surfaces, and in this study the Finnish team shows that the densest arrays of nanospikes with slightly positively tapered sidewalls had the lowest optical reflectance, while pyramid-shaped nanospikes were ideal for use as templates for polymer replication. Polymer replication techniques are typically high-throughput and low-cost methods which make them very attractive.

In this research it has been shown that both hot-embossing and UV-embossing of polymer is possible with the PDMS stamp. The use of polymers instead of silicon would be useful in high-volume applications due to lower costs. Nanospike-structured polymeric and silicon surfaces are non-reflective and additionally they can be made ultrahydrophobic and self-cleaning, by coating them with a low-surface energy coating. These kinds of inexpensive, non-reflective and self-cleaning surfaces have many applications, for instance in sensors and solar cells.

Another important issue is the mechanical durability of the nanostructured surfaces. At the moment the nanostructured surfaces damage quite easily but the team is studying ways to make the surfaces more robust.

To do this, first, an elastomeric stamp is produced by casting a PDMS layer on top of the nanospike-structured silicon surface (the original nanospikes were fabricated on full silicon wafers using the black silicon process). The PDMS is thermally cured and peeled off. Then, the PDMS stamp can be used to replicate the original nanospike pattern into other polymers, such as PMMA.

Building 3D Batteries with Coated Nanowires

The researchers at Rice University recently managed to find a way to coat nanowires with PMMA (Poly(methyl methacrylate)) coating that provides good insulation from the counter electrode while still allowing ions to pass easily through.This minimized separation between two electrodes manages to make the battery much more efficient.

In a battery, there are two electrodes separated by a thick barrier. The main objective is to bring everything into close proximity so this electrochemistry becomes much more efficient.

To achieve this, researchers took the concept of 3D batteries and coated millions of nanowires to create the 3D structure from the bottom up. By increasing the height of the nanowires, the amount of energy stored is increased while keeping the lithium ion diffusion distance constant.

The whole process involves the growing of 10-micron-long nanowires through electrodisposition in the pores of an anoidized alumina template. Then PMMA is coated onto the nanowire array, resulting in an even casing from top to bottom. The result of this work is ultimately expected to be batteries for scalable microdevices that possess a greater surface area than thin-film batteries.

Real-Time Observation of Nanowire Anode to Improve Lithium Batteries - World's Smallest Battery

A benchtop version of the world's smallest battery has been created by a team led by Sandia National Laboratories researcher. The anode of this battery is a single nanowire which is claimed to be one seven-thousandth the thickness of a human hair.

To better study the anode's characteristics, the tiny rechargeable lithium-based battery was formed inside a transmission electron microscope (TEM) at the Center for Integrated Nanotechnologies (CINT), a Department of Energy research facility jointly operated by Sandia and Los Alamos national laboratories.

This experiment facilitates the researchers to study the charging and discharging of a battery in real time and at atomic scale resolution, so that they can understand the fundamental mechanism how batteries work.

The motivation behind this work lies in the fact that current lithium ion batteries have very important application but cannot meet the demand due their low power and energy density. To improve performance they need to be investigated from the bottom up; and TEM could bring new insights to the problem.

As nanowire-based materials in lithium ion batteries significantly improved in power and energy density over bulk electrodes, more stringent investigations of their operating properties should improve new generations of plug-in hybrid electric vehicles, laptops and cell phones.

Battery research groups do use nanomaterials as anodes, but in bulk rather than individually -- a process, Scientist Huang says, that resembles "looking at a forest and trying to understand the behavior of an individual tree."

The tiny battery consists of a single tin oxide nanowire anode 100 nanometers in diameter and 10 micrometers long, a bulk lithium cobalt oxide cathode three millimeters long, and an ionic liquid electrolyte. The device offers the ability to directly observe change in atomic structure during charging and discharging of the individual wires.

An unexpected find of the researchers was that the tin oxide nanowire rod nearly doubles in length during charging which is far more than its diameter increases -- a fact that could help avoid short circuits that may shorten battery life. In future manufacturers should take account of this elongation in their battery design.

Huang's group found this flaw by following the progression of the lithium ions as they travel along the nanowire and create what researchers described as "Medusa front" defined by an area where high density of mobile dislocations cause the nanowire to bend and wiggle as the front progresses. The web of dislocations is caused by lithium penetration of the crystalline lattice. These observations prove that nanowires can sustain large stress (>10 GPa) induced by lithiation without breaking; a clear indicating that these nanowires are very good candidates for battery electrodes.

Lithiation-induced volume expansion, plasticity and pulverization of electrode materials are the major mechanical defects that plague the performance and lifetime of high-capacity anodes in lithium-ion batteries. So these observations of structural kinetics and amorphization have important implications for high-energy battery design and in mitigating battery failure.

Researchers estimated a current level of a picoampere flowing in the nanowire during charging and discharging.

Although the work was carried out using tin oxide (SnO2) nanowires, the experiments can be extended to other materials systems, either for cathode or anode studies.

The methodology that was developed should stimulate extensive real-time studies of the microscopic processes in batteries and lead to a more complete understanding of the mechanisms governing battery performance and reliability.

SUNLIGHT TO GENERATE SUPER-GREEN FUEL

In continuation with the previous article, in a breathtaking invention by the four chemists at the University of Rochester, hydrogen, which is considered to be the environmental friendly fuel in future, is thought to be produced from water using sunlight. It is also considered to be an alternative fuel source and that’s why people are trying to synthesize hydrogen through various means. In past researchers have devised many ways to produce this future fuel, but not in an environmental friendly way. This time around, they have successfully solved this problem.

"People have used sunlight to derive hydrogen from water before, but the trick is making the whole process efficient enough to be useful", commented Kara Bren, professor in the Department of Chemistry.

Bren and the rest of the Rochester team—Professor of Chemistry Richard Eisenberg, and Associate Professors of Chemistry Todd Krauss, and Patrick Holland—will be working on artificial photosynthesis, which uses sunlight to carry out chemical processes much as plants do. But people have also tried out this process; what makes the Rochester approach different from previous attempts to use sunlight to produce hydrogen from water, is that the device they are preparing is divided into three steps. Each step can be modulated, manipulated and optimized according to our need far more easily than other methods.

FIRST STEP

It uses visible light to create free electrons. A complex natural molecule called a chromophore that plants use to absorb sunlight will be re-engineered to efficiently generate reducing electrons.

SECOND STEP

In the next stage a membrane will be suffused with carbon nanotubes to act as molecular wires so small that they are only one-millionth the thickness of a human hair. To prevent the chromophores from re-absorbing the electrons, the nanotube membrane channels take the electrons away from the chromophores and push toward the third section.

THIRD STEP

In the third module, catalysts put the electrons to work forming hydrogen from water. The hydrogen can then be used in fuel cells in cars, homes, or power plants of the future.

By separating the first and third modules with the nanotube membrane, the chemists hope to isolate the process of gathering sunlight from the process of generating hydrogen. This isolation will allow the team to maximize the system's light-harvesting abilities without altering its hydrogen-generation abilities, and vice versa. Bren says this is a distinct advantage over other systems that have integrated designs because in those designs a change that enhances one trait may degrade another unpredictably and unacceptably.

NOW NANOSTRUCTURE MAKES IDEAL BATTERY

Since two decades, the whole world is concentrating on the pollution and its irreversible impact on the environmental balance. One of the prime factors that spur the environmental degradation is the pollution, created due to produce electricity. Again nanotechnology with all its uniqueness in its ability to solve any kind of technical problem comes up with a method in which environmentally friendly battery could be made by the nanostructure of algae.

Gustav Nystrom( a doctoral student in nanotechnology) who is in the team of Uppasala University in Sweden opined that the distinctive cellulose nanostructure of algae can serve as an effective coating substrate for use in environmentally friendly batteries.

According to the researchers, the algae have a special cellulose structure characterized by a very large surface area and they have coated this structure with a layer of conducting polymer. The battery almost weighs nothing and that has set new charge-time and capacity records for polymer-cellulose-based batteries.

Pharmaceutical applications of the cellulose from Cladophora algae have been explored for a number of years. This type of cellulose has a unique nanostructure, entirely different from that of terrestrial plants, that has been shown to function well as a thickening agent for pharmaceutical preparations and as a binder in foodstuffs. It is because of this huge surface area that the possibility of energy-storage applications has been raised.

This type of research creates new possibilities for large-scale production of environmentally friendly, cost-effective, lightweight energy storage systems.

GAME IS CHANGING IN SOLAR POWER!

Researchers at Rensselaer Polytechnic Institute have discovered and demonstrated a new method for overcoming two major hurdles facing solar energy. By developing a new antireflective coating that boosts the amount of sunlight captured by solar panels and allows those panels to absorb the entire solar spectrum from nearly any angle.

To get maximum efficiency when converting solar power into electricity, every single of photon of light should be absorbed by solar panel regardless of the sun’s position of the sky. New antireflective coating synthesized by the researchers makes it possible.

An untreated silicon solar cell only absorbs 67.4 percent of sunlight shone upon it — meaning that nearly one-third of that sunlight is reflected away and thus unharvestable. From an economic and efficiency perspective, this unharvested light is wasted potential and a major barrier hampering the proliferation and widespread adoption of solar power.

After a silicon surface was treated with new nano engineered reflective coating, however, the material absorbed 96.21 percent of sunlight shone upon it — meaning that only 3.79 percent of the sunlight was reflected and misutilised. This huge gain in absorption was consistent across the entire spectrum of sunlight, from UV to visible light and infrared, and moves solar power a significant step forward toward economic viability.

Typical antireflective coatings are engineered to transmit light of one particular wavelength. This new coating stacks seven of these layers, one on top of the other, in such a way that each layer enhances the antireflective properties of the layer below it. These additional layers also help to bend the flow of sunlight to an angle that augments the coating's antireflective properties. This means that each layer not only transmits sunlight, it also helps to capture any light that may have otherwise been reflected off of the layers below it.

The seven layers, each with a height of 50 nanometers to 100 nanometers, are made up of silicon dioxide and titanium dioxide nanorods positioned at an oblique angle — each layer looks and functions similar to a dense forest where sunlight is "captured" between the trees. The nanorods were attached to a silicon substrate via chemical vapor disposition.

The added advantage is that the new coating can be affixed to nearly any photovoltaic materials for use in solar cells, including III-V multi-junction and cadmium telluride.

NANO POWER: HOPE FOR THE RURAL HOMES

Now if you go to the country side and see the rooms enlightened, don't frown.Electrification of homes in rural areas would no more be a distant dream with the help of nanotechnology.

Jamshedpur-based Ekta Telecommunication and Systems is working on incorporating nanotechnology in the development of solar modules to provide electricity to all at an affordable rate. The advanced technology can be a boon for rural and urban homes. Increase in efficiency is another benefit of the technology.The technology, based on the use of a combination of solar cells to build a module and eventually a solar cell
would be developed with the use of thin polymer sheets. Electricity would be generated by placing the thin sheet on the rooftop and drawing solar the power for lighting up the entire house. “Solar electricity is the only answer to the power crisis in contemporary times.The adoption of nanotechnology would ensure that we can provide electricity to
people at prices lower than what the commercial power providers charge,” said Niraj Kumar Mishra, the chairman and managing director of Ekta Telecommunication and Systems. The company is also working on making the modules available at affordable prices. Ekta is also focussing on increasing the efficiency of the modules.The cost of the
modules would decrease to Rs 5 from the existing Rs 150 to Rs 250 per watt, said officials. The efficiency of the solar modules would go up to an average of 50 per cent from the present rate of 14 per cent.

NANO MAGIC: HYDROGEN WITHOUT CARBON

Craig A. Grimes, a professor of electrical engineering and Director of Centre of Nano Science and Technology and his team are working towards a cost effective way to produce hydrogen, previously what has been done with a very cost. They are also working on the carbon less hydrogen production.

Currently, the steam reforming of natural gas produces most of the hydrogen. As a fuel source, this produces two problems. The process uses natural gas and so does not reduce reliance on fossil fuels; and, because one byproduct is carbon dioxide, the process contributes to the carbon dioxide in the atmosphere, the carbon footprint.

Grimes' process splits water into its two components, hydrogen and oxygen, and collects the products separately using commonly available titanium and copper. Splitting water for hydrogen production is an old and proven method, but in its conventional form, it requires previously generated electricity. Photolysis of water solar splitting of water has also been explored, but is not a commercial method yet.

Grimes and his team produce hydrogen from solar energy, using two different groups of nanotubes in a photo electrochemical diode. This method generates photocurrent of approximately 0.25 milliampere per centimeter square, at a photo conversion efficiency of 0.30 percent.

"It seems that nanotube geometry is the best geometry for production of hydrogen from photolysis of water," says Grimes.

In Grimes' photo electrochemical diode, one side is a nanotube array of electron donor material - n-type material - titanium dioxide, and the other is a nanotube array that has holes that accept electrons - p-type material - cuprous oxide titanium dioxide mixture. P and n-type materials are common in the semiconductor industry. Grimes has been making n-type nanotube arrays from titanium by sputtering titanium onto a surface, anodizing the titanium with electricity to form titanium dioxide and then annealing the material to form the nanotubes used in other solar applications. He makes the cuprous oxide titanium dioxide nanotube array in the same way and can alter the proportions of each metal.

While titanium dioxide is very absorbing in the ultraviolet portion of the sun's spectrum, many p-type materials are unstable in sunlight and damaged by ultraviolet light, they photo-corrode. To solve this problem, the researchers made the titanium dioxide side of the diode transparent to visible light by adding iron and exposed this side of the diode to natural sunlight. The titanium dioxide nanotubes soak up the ultraviolet between 300 and 400 nanometers. The light then passes to the copper titanium side of the diode where visible light from 400 to 885 nanometers is used, covering the light spectrum.

The photo electrochemical diodes function the same way that green leaves do, only not quite as well. They convert the energy from the sun into electrical energy that then breaks up water molecules. The titanium dioxide side of the diode produces oxygen and the copper titanium side produces hydrogen.

Although 0.30 percent efficiency is low, Grimes notes that this is just a first go and that the device can be readily optimized.

"These devices are inexpensive and because they are photo-stable could last for years," says Grimes. "I believe that efficiencies of 5 to 10 percent are reasonable.

NANO SOLAR ENERGY

Northwestern chemistry professor Mark Ratner hopes that one day energy crisis can be solved with the help of blue jean dye and white house paint.The technology would use tiny nanostructures to convert sunlight into energy, similarly to the process of photosynthesis in plants.It's just one application of nanotechnology to the energy problem.

THE PROBLEM:


With oil prices topping $140 a barrel this week, and recent studies suggesting ethanol and other plant-based fuels may be worse for the environment than conventional fuels, pressure is growing to find a better solution. Wind and geothermal power can provide clean energy, but not enough of it. For a solution to be truly effective, it must be scalable. That is, it must produce enough energy to meet the world's needs - especially considering the rapid growth of countries like India and China.


A NEW KIND OF SOLAR PANEL:
Scientists are now trying to design solar panels using nanostructures that work like leaves, but better. The goal is 30 percent efficiency in converting sunlight into power - much higher than the efficiency of biofuels. While conventional solar panels made from silicon are about 18 percent efficient, the cost involved in making them is so high.Nanostructures, on the other hand, would use inexpensive materials to capture sunlight. That's where the blue jeans and house paint come in.



In artificial photosynthesis, you need a molecule to absorb the sunlight, but not any molecule will do. The molecules that we probably want to use are related to the blue jean dye that you've got," Ratner said. It's a planar molecule, it has the right shape and it has the right energy properties.

The dye is called a thalocyanine and is also found in shoe polish.

Once the molecules capture solar energy, that energy must be stored somewhere - otherwise, it will be given off as heat. White house paint contains titanium dioxide, and when mixed with the dye molecules, titanium dioxide holds on to the energy the dye collects.