September 30, 2014 | Leave a Comment
Scientists at Ecole Polytechnique Fédérale de Lausanne (EPFL) have developed a new and efficient way of producing hydrogen fuel from sunlight and water. Connecting together solar cells made with a mineral called perovskite and the team’s low cost electrodes achieves a 12.3 percent conversion efficiency from solar energy to hydrogen.
The profusion of tiny bubbles escaping from the electrodes as soon as the solar cells are exposed to light say it better than words ever could: the combination of sun and water paves a promising and effervescent way for developing the energy of the future.
The 12.3 percent efficiency establishes a new non rare earth element process record. Absent platinum the costs for building a solar powered hydrogen production process is greatly reduced.
The Laboratory of Photonics and Interfaces at EPFL is led by Michael Grätzel, and is where scientists invented dye solar cells that mimic photosynthesis in plants. Now they have also developed a method for generating fuel such as hydrogen through solar water splitting.
Grätzel’s post-doctoral student Jingshan Luo and his colleagues using the new process were able to obtain a performance so spectacular that their achievement has been published in the journal Science. This efficiency number is no small breakout for the technology.
The team’s device converts into hydrogen at 12.3 percent of the energy diffused by the sun on perovskite absorbers – perovskite is a compound that can be obtained in the laboratory from common materials, such as those used in conventional car batteries, eliminating the need for rare-earth metals in the production of usable hydrogen fuel.
There is a wide array of research underway to optimize solar energy’s performance. There are more silicon photovoltaic panels, dye-sensitized solar cells, concentrated cells and thermodynamic solar plants all pursuing the same goal of producing a maximum amount of electrons from sunlight. Those electrons can then be converted into electricity to run the lights, power up appliances and energize our electronic devices.
The new process provides stiff competition for other techniques used to convert solar energy with several advantages.
Jingshan Luo explains, “Both the perovskite used in the cells and the nickel and iron catalysts making up the electrodes require resources that are abundant on Earth and that are also cheap. However, our electrodes work just as well as the expensive platinum based models customarily used.”
In the next step, the conversion of solar energy into hydrogen, makes solar energy storage possible. That addresses one of the biggest disadvantages faced by renewable electricity – the requirement to use the energy at the time it is produced.
Grätzel points out, “Once you have hydrogen, you store it in a bottle and you can do with it whatever you want to, whenever you want it.” Hydrogen gas can indeed be burned – in a boiler or engine – releasing only water vapor. It can also pass into a fuel cell to generate electricity on demand. Grätzel promises in the press release the 12.3% conversion efficiency achieved at EPFL “will soon get even higher”.
The breakout efficiency is based on a characteristic of perovskite cells which is their ability to generate an open circuit voltage greater than 1V while compared to silicon cells that stop at 0.7V.
Jingshan Luo explains, “A voltage of 1.7V or more is required for water electrolysis to occur and to obtain exploitable gases.” To get these numbers, three or more silicon cells are needed, whereas just two perovskite cells are enough. As a result, there is more efficiency with respect to the surface of the light absorbers required. “This is the first time we have been able to get hydrogen through electrolysis with only two cells!” exclaims Luo.
The solar driven hydrogen production effort is starting to look very good, indeed.
September 25, 2014 | 2 Comments
Sandia’s scientists report that working with two magnetic fields and a laser, all at low points of their power outputs, the Z machine has released neutrons in an amount surprisingly close to ‘break-even’ fusion. The new result comes from using a method fully functioning for only little more than a year.
A theoretical Physical Review Letterspaper to be published on the same date helps explain why the experimental method worked. The combined work demonstrates the viability of the novel approach.
Sandia senior manager Dan Sinars said, “We are committed to shaking this [fusion] tree until either we get some good apples or a branch falls down and hits us on the head.” He expects the project, dubbed “MagLIF” for magnetized liner inertial fusion, will be “a key piece of Sandia’s submission for a July 2015 National Nuclear Security Administration review of the national Inertial Confinement Fusion Program.”
Inertial confinement fusion creates nanosecond bursts of neutrons, ideal for creating data to plug into supercomputer codes that test the safety, security and effectiveness of the U.S. nuclear stockpile. The method could be useful as an energy source down the road if the individual fusion pulses can be sequenced like an automobile’s cylinders firing.
MagLIF uses a laser to preheat hydrogen fuel, a large magnetic field to squeeze the fuel and a separate magnetic field to keep charged atomic particles from leaving the scene.
It only took the two magnetic fields and the laser, focused on a small amount of fusible material called deuterium (hydrogen with a neutron added to its nucleus), to produce a trillion fusion neutrons (neutrons created by the fusing of atomic nuclei). Had tritium (which carries two neutrons) been included in the fuel, scientific rule-of-thumb says that 100 times more fusion neutrons would have been released. (That is, the actual release of 10 to the 12th neutrons would be upgraded, by the more reactive nature of the fuel, to 10 to the 14th neutrons.)
Tritium’s even larger output, to achieve break-even fusion – as much power out of the fuel as placed into it – will still need 100 times more neutrons (10 to the 16th) to be produced.
That’a a sizable gap, but the Sandia technique is an experiment with researchers still figuring out the simplest measures: how thick or thin key structural elements of the design should be and the relation between the three key aspects of the approach – the two magnetic fields and the laser. There will lots of room for improvement as things progress.
The first paper, “Experimental Demonstration of Fusion-Relevant Conditions in Magnetized Liner Inertial Fusion,” (MagLIF) by Sandia lead authors Matt Gomez, Steve Slutz and Adam Sefkow, describes a fusion experiment remarkably simple to visualize.
The deuterium target atoms are placed within a long thin tube called a liner. A magnetic field from two pancake-shaped (Helmholtz) coils above and below the liner creates an electromagnetic curtain that prevents charged particles, both electrons and ions, from escaping. The extraordinarily powerful magnetic field of Sandia’s Z machine then crushes the liner like an athlete crushing a soda can, forcefully shoving atoms in the container into more direct contact. As the crushing begins, a laser beam preheats the deuterium atoms, infusing them with energy to increase their chances of fusing at the end of the implosion. (A nuclear reaction occurs when an atom’s core is combined with that of another atom, releasing large amounts of energy from a small amount of source material. That outcome is important in stockpile stewardship and, eventually, in civilian energy production.) Trapped energized particles including fusion-produced alpha particles (two neutrons, two protons) also help maintain the high temperature of the reaction.
Sefkow noted, “On a future facility, trapped alpha particles would further self-heat the plasma and increase the fusion rate, a process required for break-even fusion or better.”
The actual MagLIF procedure follows this order: The Helmholtz coils are turned on for a few thousandths of a second. Within that relatively large amount of time, a 19-megaAmpere electrical pulse from Z, with its attendant huge magnetic field, fires for about 100 nanoseconds or less than a millionth of a second with a power curve that rises to a peak and then falls in intensity. Just after the 50-nanosecond mark, near the current pulse’s peak intensity, the laser, called Z-Beamlet, fires for several nanoseconds, warming the fuel.
According to the paper’s authors, the unusual arrangement of using magnetic forces both to collapse the tube and simultaneously insulate the fuel, keeping it hot, means researchers could slow down the process of creating fusion neutrons. What had been a precipitous process using X-rays or lasers to collapse a small unmagnetized sphere at enormous velocities of 300 kilometers per second, can happen at about one-quarter speed at a much more “modest” 70 km/sec. (“Modest” is used as a comparative term; the speed is about six times greater than that needed to put a satellite in orbit.)
The slower pace allows more time for fusible reactions to take place. The more benign implosion also means fewer unwanted materials from the collapsing liner mix into the fusion fuel, which would cool it and prevent fusion from occurring. By analogy, a child walking slowly in the ocean’s shallows stirs less mud than a vigorously running child.
Sandia senior scientist Mike Campbell said, “This experiment showed that fusion will still occur if a plasma is heated by slow, rather than rapid, compression. With rapid compression, if you mix materials emitted from the tube’s restraining walls into the fuel, the fusion process won’t work; also, increased acceleration increases the growth of instabilities. A thicker can [tube] is less likely to be destroyed when contracted, which would dump unwanted material into the deuterium mix, and you also reduce instabilities, so you win twice.”
Besides the primary deuterium fusion neutron yields, the team’s measurements also found a smaller secondary deuterium-tritium neutron signal, about a hundredfold larger than what would have been expected without magnetization, providing a smoking gun for the existence of extreme magnetic fields.
The question remained whether it was indeed the secondary magnetic field that caused the 100-fold increase in this additional neutron pulse, or some other, still unknown cause. Fortunately, the pulse has a distinct nuclear signature arising from the interaction of tritium nuclei as they slow down and react with the primary deuterium fuel, and that interaction was detected by Sandia sensors.
The secondary magnetic field is the subject of the second, theoretical paper, “Understanding Fuel Magnetization and Mix Using Secondary Nuclear Reactions in Magneto-Inertial Fusion.” Using simulations, Sandia researchers Paul Schmit, Patrick Knapp, et al confirmed the existence and effect of extreme magnetic fields. Their calculations showed that the tritium nuclei would be encouraged by these magnetic fields to move along tight helical paths. This confinement increased the probability of subsequently fusing with the main deuterium fuel.
“This dramatically increases the probability of fusion,” Schmit said. “That it happened validates a critical component of the MagLIF concept as a viable pathway forward for fusion. Our work has helped show that MagLIF experiments are already beginning to explore conditions that will be essential to achieving high yield and/or ignition in the future.”
The foundation of Sandia’s MagLIF work is based on work led by Slutz. In a 2010 Physics of Plasmas article, Slutz showed that a tube enclosing preheated deuterium and tritium, crushed by the large magnetic fields of the 27-million-ampere Z machine and a secondary magnetic field, would yield slightly more energy than is inserted into it.
A later simulation, published January 2012 in Physical Review Letters by Slutz and Sandia researcher Roger Vesey, showed that a more powerful accelerator generating 60 million amperes or more could reach “high-gain” fusion conditions, where the fusion energy released exceeds by more than 1,000 times the energy supplied to the fuel.
This results shows the concept has legs and might get to breakeven. But, said Campbell, “There is still a long way to go.” But they are way ahead of ITER,
Researchers have looked far and wide for microbes that break down hemicellulose focusing over the past years on termite gut microbes because they breakdown wood tissues effectively and cow stomach rumens because those microbes break down the hemicellulose from grass plants quite well.
The UI scientist’s study has been published in the Proceedings of the National Academy of Sciences. The UI team’s work is the first to use biochemical approaches to confirm the hypothesis that microbes in the human gut can digest fiber, breaking it down into simple sugars in order to ferment them into nutrients that nourish human cells.
That seems to be a reversal of logic, but a longer look could consider that natural sugars, the food for yeasts that make ethanol, are very much the same as what humans need for energy in their diets. The new findings have significance for human health as well as for biofuels production, since the same sugars can be fed to yeast to generate ethanol and other liquid fuels.
The human microbes appear to be endowed with enzymes that break down a complex plant fiber component more efficiently than the most efficient microbes found in the cow rumen.
University of Illinois animal sciences and Institute for Genomic Biology professor Isaac Cann, who led the new analysis noted their work in cows led the researchers to the human microbes. Cann also is a microbiology professor and a principal investigator at the Energy Biosciences Institute. A principal colleague is UI animal sciences professor Roderick Mackie.
Cann said, “In looking for biofuels microbes in the cow rumen, we found that Prevotella bryantii, a bacterium that is known to efficiently break down (the plant fiber) hemicellulose, gears up production of one gene more than others when it is digesting plant matter.”
When searching a database for similar genes in other organisms, the scientists found them in microbes from the human gut. The team focused on two of these human microbes, Bacteroides intestinalis and Bacteroides ovatus, which belong to the same bacterial phylum as Prevotella from the cow.
“We expressed the human gut bacterial enzymes and found that for some related enzymes, the human ones actually were more active (in breaking down hemicellulose) than the enzymes from the cow,” Cann said.
When the scientists looked more closely at the structure of the human enzymes, they saw something unusual: many single polypeptide (protein) chains actually contained two enzymes, one of which was embedded in the other. Further analysis of the most important protein revealed that the embedded component was a carbohydrate-binding module (CBM), which, as its name implies, latches onto carbohydrates such as hemicellulose. This enzyme shreds the plant fiber hemicellulose so that other enzymes can work on it to break it down into its unit sugars.
Working with UI biochemistry professor Satish Nair, the scientists also noticed that the CBM “put a kink” in the fiber when it bound to it. This bending action may bring the fiber close to the other enzyme in the protein so it can get to work breaking the bonds between the sugars. Further research is needed to confirm this hypothesis, Cann said.
The study points to human microbes as a potentially potent source of microbes that can aid in biofuels production. Cann said, “In addition to finding microbes in the cow rumen and termite gut, it looks like we can actually make some contributions ourselves. And our bugs seem to have some enzymes that are even better than those in the cow rumen.”
The news might not seem hugely significant, but it has been published in a very significant journal. Team member Dylan Dodd M.D. and Ph.D. student is now at Stanford University where biofuel work is a major effort. For all the looking far and wide a truly interesting and high potential and so far unique enzyme pair loaded into an effective and active polypeptide chains has now been found – up close, really close by.
September 23, 2014 | Leave a Comment
University of Massachusetts Amherst (UMass) scientists have developed a more efficient, easily processed and lightweight solar cell that can use virtually any metal for the electrode, effectively breaking the “electrode barrier.” Polymer scientists and synthetic chemists have been working for decades to improve the power conversion efficiency of organic solar cells. The effort has been hampered by the inherent drawbacks of commonly used metal electrodes, due their instability, susceptibility to oxidation and other issues.
UMass’s Thomas Russell, professor of polymer science and engineering describes a barrier that has bedeviled research, “The sun produces 7,000 times more energy per day than we can use, but we can’t harness it well. One reason is the trade-off between oxidative stability and the work function of the metal cathode.” Work function relates to the level of difficulty electrons face as they transfer from the solar cell’s photoactive layer to the electrode that delivers the power to a device.
Russell likes to use a lock-and-dam analogy to talk about electron transfer. “People have thought you’d need to use tricks to help electrons, the water in the lock, over an obstacle, the electrode, like a dam. Tricks like sawing the dam apart to allow the flow. But tricks are always messy, introducing a lot of stuff you don’t need,” he says. “The beauty of the solution reached by these synthetic chemists is to just move the dam out of the way, electronically move it so there is no longer a difference in energy level.”
Synthetic chemist and polymer science professor Todd Emrick agrees, “That challenge was unmet and that’s what this research is all about.” He and polymer chemistry doctoral student Zak Page in his lab had been synthesizing new polymers with zwitterions on them, applying them to several different polymer scaffolds in conjugated systems, also known as semiconductors, in the inter-layer of solar cells. Zwitterions are neutral molecules with both a positive and negative charge that also have strong dipoles that interact strongly with metal electrodes, the scientists found.
Emrick asked Page to see if he could synthesize conjugated polymers, semiconductors, with zwitterionic functionality. With time, and by enlisting a system of multiple solvents including water, Page was able to prepare these new “conjugated polymer zwitterions,” or “CPZs”.
Emrick explains, “Once we could make CPZs, we were able to incorporate any conjugated backbone we wanted with zwitterionic functionality. That allowed us to make a library of CPZs and look at their structure-property relationship to understand which would be most important in electronics. In particular, we were interested in electron transport efficiency and how well the CPZ could modify the work function of different metals to help move electrons across interfaces towards more powerful devices.
Page explained that in choosing a metal for use as an electrode, scientists must always negotiate a trade-off. More stable metals that don’t degrade in the presence of water and oxygen have high work function, not allowing good electron transport. But metals with lower work function (easier electron transport) are not stable and over time will degrade, becoming less conductive. That pulls out the power generated with resistance shedding the energy out as heat.
Page was guided by UMass Amherst’s photovoltaic facility director Volodimyr Duzhko in using ultraviolet photoelectron spectroscopy (UPS). Page categorized several metals including copper, silver and gold, to identify exactly what aided electron transport from the photoactive layer to the electrode. Page and Emrick found that “if you want to improve the interlayer properties, you have to make the interface layer extremely thin, less than 5 nanometers, which from a manufacturing standpoint is a problem,” he said.
To solve the problem Page and Emrick began to consider a classic system known for its good electron transport: buckyballs, or fullerenes, often used in the photoactive layer of solar cells. “We modified buckyballs with zwitterions (C60-SB) to change the work function of the electrodes, and we knew how to do that because we had already done it with polymers,” Page pointed out. “We learned how to incorporate zwitterion functionality into a buckyball as efficiently as possible, in three simple steps.”
That’s when the synthetic chemists turned to Russell’s postdoctoral researcher Yao Liu, giving him two different fullerene layers to test for electron transfer efficiency: C60-SB and another with amine components, C60-N. From UPS analysis of the zwitterion fullerene precursor, Page suspected that the amine type would enhance power even better than the C60-SB variety. Indeed, Liu found that a thin layer of C60-N between the solar cell’s photoactive layer and the electrode worked best, and the layer did not have to be ultra-thin to function effectively, giving this discovery substantial practical advantages.
Page said, “That’s when we knew we had something special.”
Emrick added, “This is really a sweeping change in our ability to move electrons across dissimilar materials. What Zak did is to make polymers and fullerenes that change the qualities of the metals they contact, that change their electronic properties, which in turn transforms them from inefficient to more efficient devices than had been made before.”
Russell offered, “Their solution is elegant, their thinking is elegant and it’s really easy and clean. You put this little layer on there, it doesn’t matter what you put on top, you can use robust metals that don’t oxidize. I think it’s going to be very important to a lot of different scientific communities.”
This could be a major manufacturing step into the future. Electrical junctions such as soldered connections, must number in the trillions across the world’s electronic and electrical device fleet. If the research leads to a new connection method that reduces resistance, power needs would be reduced, labor costs cut back and the toxicity of electronic waste would go down as well. Lets hope the research goes on to join the full array of electrical connections and some work includes the mechanical strength aspect as well.
University of Missouri-Columbia (MU) researchers have created a long-lasting and more efficient nuclear battery. Its built from a radioactive isotope called strontium 90 that boosts electrochemcial energy in a water-based solution with a nanostructured titanium dioxide electrode with a platinum coating collecting and effectively converting energy into electrons.
The idea has many high power applications such as a reliable energy source in automobiles and also in complicated applications such as space flight. Its a superlative idea that is now working.
Jae W. Kwon, an associate professor of electrical and computer engineering and nuclear engineering in the College of Engineering at MU said, “Betavoltaics, a battery technology that generates power from radiation, has been studied as an energy source since the 1950s. Controlled nuclear technologies are not inherently dangerous. We already have many commercial uses of nuclear technologies in our lives including fire detectors in bedrooms and emergency exit signs in buildings.”
The nuclear name part is going to be the problem. After all, strontium 90 is a long way from uranium 235 or plutonium 244 (atomic numbers respectively, 38, 92 & 94). Strontium 90 is a beta emitter, the radiation energy that powers the battery. Still, beta emitters are not something a home shop operator should be working with, as light shielding is required. Sealed within few millimeters of aluminum would do.
Kwon explains the system, “Water acts as a buffer and surface plasmons created in the device turned out to be very useful in increasing its efficiency. The ionic solution is not easily frozen at very low temperatures and could work in a wide variety of applications including car batteries and, if packaged properly, perhaps spacecraft.”
The MU battery demonstrates that liquids can be an excellent media for effective energy conversion from radioisotopes. The water based ionic fluid is also contributes to the shielding. The battery is also a direct conversion method producing electric power straight from energetic particles rather than an indirect conversion methods such as collecting electricity from the secondary energy forms of heat or light.
How the battery works is the beta particles produce electron-hole pairs in semiconductors via their loss of kinetic energy and can contribute to the generation of electric power.
So far the solid beta decay battery design problem has been serious radiation damage to the lattice structures of semiconductors and subsequent performance degradation due to the high kinetic energy of the beta particles pounding the solid construction to pieces.
The MU battery stands out with the major benefit of utilizing a liquid-phase material and the liquid’s well-known ability to efficiently absorb the kinetic energy of beta particles. The fluid absorbs the energy and passes much of it to the semiconductor.
This is where the innovation or breakthrough comes in. Since the advent of nuclear power, liquids have been intensively studied for use as a radiation-shielding material. Large amounts of radiation energy can be absorbed by water. When radiation energy is absorbed by an aqueous solution, free radicals can be produced through radiolytic interactions. The MU battery demonstrates a new method for the generation of electricity using a device that separates the radiolytic current from the free radicals by splitting the water.
The water splitter is composed of a nanoporous semiconductor coated with a thin platinum film to produce a specially designed metal-semiconductor junction. For the semiconductor they used a very stable and common large band gap oxide material, titanium dioxide (white paint pigment), because of the large band gap oxide materials offer as a semiconducting catalyst that can improve the radiolysis yield.
What happens is during the spitting high-energy beta radiation the device can produce free radicals in water through the loss of kinetic energy. In a meta-stable state, the free radicals are recombined into water molecules or trapped in water molecules. Then the free radicals produced by the radiation can be converted into electricity by a plasmon-assisted, wide band gap oxide semiconducting material.
How good is this first lab theory test battery? Hold on to something . . .
The maximum energy conversion efficiency of the MU battery was approximately estimated to be 53.88%. This is an astonishing number for a first trial design.
That’s enough for a news type of posting. For more information the paper can be read in full online at this writing. Some of you are going to realize that strontium 90 has a half life of 28.79 years. The implications of that thought are mind boggling.