Scientists at the University of Illinois at Chicago (UIC) have synthesized a catalyst that improves their system for converting waste carbon dioxide into syngas. Syngas can be a precursor of gasoline and other energy-rich products with the UIC work bringing the process closer to commercial viability.
Your humble writer has watching this group for some years now and admires that they grasp the concept of “more better and cheaper”.
Amin Salehi-Khojin, UIC professor of mechanical and industrial engineering said, “Our whole purpose is to move from laboratory experiments to real-world applications. This is a real breakthrough that can take a waste gas – carbon dioxide – and use inexpensive catalysts to produce another source of energy at large-scale, while making a healthier environment.”
Salehi-Khojin, principal investigator on the study and his coworkers have developed a unique two-step catalytic process that uses molybdenum disulfide, the often used metallic friction agent, and an ionic liquid to “reduce,” or transfer electrons, to carbon dioxide in a chemical reaction. The new catalyst improves efficiency and lowers cost by replacing expensive metals like gold or silver in the reduction reaction.
Mohammad Asadi, UIC graduate student and co-first author on the paper said the discovery is a big step toward industrialization. “With this catalyst, we can directly reduce carbon dioxide to syngas without the need for a secondary, expensive gasification process,” he said. In other chemical-reduction systems, the only reaction product is carbon monoxide. The new catalyst produces syngas, a mixture of carbon monoxide plus hydrogen.
This announcement is a major repositioning of the potential involved in carbon dioxide recycling. It should be of great interest to any firm combusting fuels and emitting CO2 – the technology could very well reduce costs by making a market for the effluents that aggravate so many.
Salehi-Khojin explains, “This is a very generous material. We are able to produce a very stable reaction that can go on for hours.” The high density of loosely bound, energetic d-electrons in molybdenum disulfide facilitates charge transfer, driving the reduction of the carbon dioxide.
Bijandra Kumar, UIC post-doctoral fellow and co-first author of the paper said, “In comparison with other two-dimensional materials like graphene, there is no need to play with the chemistry of molybdenum disulfide, or insert any host materials to get catalytic activity.”
Graduate student Amirhossein Behranginia, a coauthor on the paper explained, “In noble metal catalysts like silver and gold, catalytic activity is determined by the crystal structure of the metal, but with molybdeneum disulfide, the catalytic activity is on the edges. Fine-tuning of the edge structures is relatively simple. We can easily grow the molybdenum disulfide with the edges vertically aligned to offer better catalytic performance.”
Salehi-Khojin, pleased with the new catalysts versatility noted that the proportion of carbon monoxide to hydrogen in the syngas produced in the reaction can also be easily manipulated using the new catalyst.
One has to admire this group, everyone is credited. Artem Baskin, Nikita Repnin, Davide Pisasale, Patrick Philips, Robert Klie, Petr Kral and Jeremiah Abiade of UIC; Brian Rose and Richard Haasch of the University of Illinois at Urbana-Champaign; and Wei Zhu of Dioxide Materials in Champaign, Illinois, are also coauthors on the paper.
This process technology is getting better every year. Is has a great story based on fuel combusted followed with effluent reprocessed back to fuel again. Lets wish more breakthroughs on this team.
Stanford researchers report that they have taken a big step toward designing a pure lithium anode – an accomplishment that battery designers have been trying to do for decades.
Chemical batteries have three basic components: an electrolyte to provide electrons, an anode to discharge those electrons out to a circuit, and a cathode to receive them back.
Yi Cui, a Stanford professor of Material Science and Engineering and leader of the research team explains, “Of all the materials that one might use in an anode, lithium has the greatest potential. Some call it the Holy Grail. It is very lightweight and it has the highest energy density. You get more power per volume and weight, leading to lighter, smaller batteries with more power.”
Today, we say we have lithium batteries, but that is only partly true. What we have are lithium ion batteries. The lithium is in the electrolyte, but not in the anode. An anode of pure lithium would be a huge boost to battery efficiency.
Research scientists and engineers across the globe have been racing to design smaller, cheaper and more efficient rechargeable batteries to meet the power storage needs of everything from handheld gadgets to electric cars. But engineers have long tried and failed to reach Cui’s Holy Grail.
Guangyuan Zheng, a doctoral candidate in Cui’s lab and first author of the paper explains further, “Lithium has major challenges that have made its use in anodes difficult. Many engineers had given up the search, but we found a way to protect the lithium from the problems that have plagued it for so long.”
Steven Chu, the former U.S. Secretary of Energy and Nobel Laureate who recently resumed his professorship at Stanford, “In practical terms, if we can improve the capacity of batteries to, say, four times today’s, that would be exciting. You might be able to have cell phone with double or triple the battery life or an electric car with a range of 300 miles that cost only $25,000 – competitive with an internal combustion engine getting 40 mpg.”
Stanford has rolled out the big names for this one.
In the paper, the authors explain how they are overcoming the problems posed by lithium.
Most lithium ion batteries, like those you might find in your cell phone or hybrid car, work similarly. The key components include an anode, the negative pole from which electrons flow out and into a power-hungry device, and the cathode, where the electrons re-enter the battery once they have traveled through the circuit. Separating them is an electrolyte, a solid or liquid loaded with positively charged lithium ions that travel between the anode and cathode.
During charging, the positively charged lithium ions in the electrolyte are attracted to the negatively charged anode and the lithium accumulates on the anode. Today, the anode in a lithium ion battery is actually made of graphite or silicon.
Engineers would like to use lithium for the anode, but so far they have been unable to do so. That’s because the lithium ions expand as they gather on the anode during charging.
All anode materials, including graphite and silicon, expand somewhat during charging, but not like lithium. Researchers say that lithium’s expansion during charging is “virtually infinite” relative to the other materials. Its expansion is also uneven, causing pits and cracks to form in the outer surface, like paint on the exterior of a balloon that is being inflated.
The resulting fissures on the surface of the anode allow the precious lithium ions to escape, forming hair-like or mossy growths, called dendrites. Dendrites, in turn, short circuit the battery and shorten its life. Dendrites are also implicated in lithium battery fires.
Preventing this buildup is the first challenge of using lithium for the battery’s anode.
The second engineering challenge is that a lithium anode is highly chemically reactive with the electrolyte. It uses up the electrolyte and reduces battery life.
An additional problem is that the anode and electrolyte produce heat when they come into contact. Lithium batteries, including those in use today, can overheat to the point of fire, or even explosion, and are, therefore, a serious safety concern. The recent battery fires in Tesla cars and on Boeing’s Dreamliner are prominent examples of the challenges of lithium ion batteries.
The Stanford solution to solve the problems is build a protective layer of interconnected carbon domes on top of their lithium anode. This layer is what the team has called “nanospheres”.
The Stanford team’s nanosphere layer resembles a honeycomb: it creates a flexible, uniform and non-reactive film that protects the unstable lithium from the drawbacks that have made it such a challenge. The carbon nanosphere wall is just 20 nanometers thick. It would take some 5,000 layers stacked one atop another to equal the width of single human hair.
“The ideal protective layer for a lithium metal anode needs to be chemically stable to protect against the chemical reactions with the electrolyte and mechanically strong to withstand the expansion of the lithium during charge,” Cui said.
The Stanford nanosphere layer is just that. It is made of amorphous carbon, which is chemically stable, yet strong and flexible so as to move freely up and down with the lithium as it expands and contracts during the battery’s normal charge-discharge cycle.
In technical terms, the nanospheres improve the coulombic efficiency of the battery – a ratio of the amount of lithium that can be extracted from the anode when the battery is in use compared to the amount put in during charging. A single round of this give-and-take process is called a cycle.
Generally, to be commercially viable, a battery must have a coulombic efficiency of 99.9 percent or more, ideally over as many cycles as possible. Previous anodes of unprotected lithium metal achieved approximately 96 percent efficiency, which dropped to less than 50 percent in just 100 cycles, which is not nearly good enough. The Stanford team’s new lithium metal anode achieves 99 percent efficiency even at 150 cycles.
“The difference between 99 percent and 96 percent, in battery terms, is huge. So, while we’re not quite to that 99.9 percent threshold, where we need to be, we’re close and this is a significant improvement over any previous design,” Cui said. “With some additional engineering and new electrolytes, we believe we can realize a practical and stable lithium metal anode that could power the next generation of rechargeable batteries.”
No word on the cost of interconnected carbon domes applied to an anode either in the lab or at commercial scale. The Stanford team is an impressive group, but carbon nanospheres aren’t exactly a new thing. Building up to a battery anode is.
So far very few of the breakthroughs have made it to market. Yet somehow a few breakthroughs do find their way to engineers that can take what is known and build something that sells for a profit.
Lots of potential here, time will tell.
Physicists led by Dirk Morr, professor of physics at the University of Illinois at Chicago (UIC), and experimentalists led by Seamus J.C. Davis of Cornell University and Brookhaven National Laboratory have identified the ‘quantum glue’ that underlies a promising type of superconductivity – a crucial step towards the creation of energy superhighways that conduct electricity without current loss. This could be a major news event starting point as more progress is made.
The background has superconductivity arising when two electrons in a material become bound together, forming what is called a Cooper pair with the earliest superconducting materials requiring operating temperatures near absolute zero, or −459.67 º Fahrenheit. Newer unconventional or “high-temperature” superconductors function at slightly elevated temperatures and seemed to work differently from the first found materials. Scientists hoped this difference hinted at the possibility of superconductors that could work at room temperature and be used to create energy superhighways.
Groundbreaking experiments performed by Freek Massee and Milan Allan in Davis’s group were analyzed using a new theoretical framework developed at UIC by Morr and graduate student John Van Dyke, who is first author on the report. Their results pointed to magnetism as the force underlying the superconductivity in an unconventional superconductor consisting of cerium, cobalt and indium, with the molecular formula CeCoIn5.
Morr, the principal investigator on the study said, “For a long time, we were unable to develop a detailed theoretical understanding of this unconventional superconductor.” Two crucial insights into the complex electronic structure of CeCoIn5 were missing, he explained: the relation between the momentum and energy of electrons moving through the material, and the ‘quantum glue’ that binds the electrons into a Cooper pair.
Those questions were answered after the Davis group developed high-precision measurements of CeCoIn5 using a scanning tunneling spectroscopy technique called quasi-particle interference spectroscopy. Analysis of the spectra using a novel theoretical framework developed by Morr and Van Dyke allowed the researchers to extract the missing pieces of the puzzle.
The new insight allowed them to explore the 30-year-old hypothesis that the quantum glue of superconductivity is the magnetic force.
Morr explained, ” Magnetism is highly directional. Knowing the directional dependence of the quantum glue, we were able, for the first time, to quantitatively predict the material’s superconducting properties using a series of mathematical equations.”
“Our calculations showed that the gap possesses what’s called a d-wave symmetry, implying that for certain directions the electrons were bound together very strongly, while they were not bound at all for other directions,” Morr said. Directional dependence is one of the hallmarks of unconventional superconductors.
“We concluded that magnetism is the quantum glue underlying the emergence of unconventional superconductivity in CeCoIn5.”
The finding has “lifted the fog of complexity” surrounding the material, Morr said, and was only made possible by “the close collaboration of theory and experiment, which is so crucial in advancing our understanding of complex systems.”
“We now have an excellent starting point to explore how superconductivity works in other complex material,” Morr said. “With a working theory, we can now investigate how we have to tweak the system to raise the critical temperature – ideally, all the way up to room temperature.
We can come away from the news with two notable points. The first is directional superconductivity suggests that the use with be for carrying DC current. Not a show stopper at all but a point worth keeping in mind in the coming years. The second is the theorization with experimental follow up has important implications for researchers. Some ideas of the past might deserve another look.
This research seems to be quite an intellectual exercise with very promising results. A major crack in the fence holding back superconductivity has now been found.
Yulia Pushkar, a Purdue assistant professor of physics involved in the research said, “The proteins we study are part of the most efficient system ever built, capable of converting the energy from the sun into chemical energy with an unrivaled 60 percent efficiency. Understanding this system is indispensable for alternative energy research aiming to create artificial photosynthesis.”
The process by which plants convert the sun’s energy into carbohydrates is used to power the cellular processes. During photosynthesis plants use solar energy to convert carbon dioxide and water into hydrogen-storing carbohydrates and oxygen. Artificial photosynthesis could allow for the conversion of solar energy into renewable, environmentally friendly hydrogen-based fuels.
In Pushkar’s laboratory, students extract a protein complex called Photosystem II from spinach they buy at the supermarket. It is a complicated process performed over two days in a specially built room that keeps the spinach samples cold and shielded from light, she said.
Once the proteins have been carefully extracted, the team excites them with a laser and records changes in the electron configuration of their molecules.
“These proteins require light to work, so the laser acts as the sun in this experiment,” Pushkar said. “Once the proteins start working, we use advanced techniques like electron paramagnetic resonance and X-ray spectroscopy to observe how the electronic structure of the molecules change over time as they perform their functions.”
The idea is to figure out how Photosystem II is involved in the photosynthetic mechanism that splits water molecules into oxygen, protons and electrons. During this process a portion of the protein complex, called the oxygen-evolving complex, cycles through five states in which four electrons are extracted from it, Pushkar said.
Petra Fromme, professor of chemistry and biochemistry at Arizona State University, leads the international team that recently revealed the structure of the first and third states at a resolution of 5 and 5.5 Angstroms, respectively, using a new technique called serial femtosecond crystallography. A paper detailing the results was published in Nature and is available online.
In addition to Pushkar, Purdue postdoctoral researcher Lifen Yan and former Purdue graduate student Katherine Davis participated in the study and are paper co-authors.
Fromme explained in a statement, “The trick is to use the world’s most powerful X-ray laser, named LCLS, located at the Department of Energy’s SLAC National Accelerator Laboratory. Extremely fast femtosecond (one-quadrillionth of a second) laser pulses record snapshots of the PSII crystals before they explode in the X-ray beam, a principle called ‘diffraction before destruction.’”
While X-ray crystallography reveals structural changes, it does not provide details of how the electronic configurations evolve over time, which is where the Purdue team’s work came in. The Purdue team mimicked the conditions of the serial femtosecond crystallography experiment, but used electron paramagnetic resonance to reveal the electronic configurations of the molecules, Pushkar said.
“The electronic configurations are used to confirm what stage of the process Photosystem II is in at a given time,” she said. “This information is kind of like a time stamp and without it the team wouldn’t have been able to put the structural changes in context.”
The Arizona State University (ASU) press release hints that the team will get to a moving picture over time. The study that shows the first snapshots of photosynthesis in action as it splits water into protons, electrons and oxygen – the process that maintains Earth’s oxygen atmosphere.
The revealing of the mechanism of this water splitting process is essential for the development of artificial systems that mimic and surpass the efficiency of natural systems. The development of an “artificial leaf” is one of the major goals of the ASU Center for Bio-Inspired Solar Fuel Production, which was the main supporter of this study.
ASU Regents’ Professor Devens Gust in a connected paraphrase sums up, “A crucial problem is discovering an efficient, inexpensive catalyst for oxidizing water to oxygen gas, hydrogen ions and electrons. Photosynthetic organisms already know how to do this, and we need to know the details of how photosynthesis carries out the process using abundant manganese and calcium. The research gives us a look at how the catalyst changes its structure while it is working. Once the mechanism of photosynthetic water oxidation is understood, chemists can begin to design artificial photosynthetic catalysts that will allow them to produce useful fuels using sunlight.”
Its known that in photosynthesis, oxygen is produced at a special metal site containing four manganese atoms and one calcium atom, connected together as a metal cluster. This oxygen-evolving cluster is bound to the protein Photosystem II that catalyzes the light-driven process of water splitting. It requires four light flashes to extract one molecule of oxygen from two water molecules bound to the metal cluster.
The ultimate goal of the work is to record molecular movies of water splitting.
For now the researchers discovered large structural changes of the protein and the metal cluster that catalyzes the reaction. The cluster significantly elongates, thereby making room for a water molecule to move in.
Its a large team that is getting to the point they understand what is happening at the level of atoms inside the molecule. Its only a matter of time until a protein can be made to accomplish the job in an artificial way.
July 23, 2014 | 1 Comment
Shanhui Fan, an electrical engineering professor at Stanford University in California has found a way to let photovoltaic solar cells cool themselves by shepherding away unwanted thermal radiation. By adding a specially patterned layer of silica glass to the surface of ordinary solar cells, a team of researchers may have overcome one of the major hurdles in developing high-efficiency, long-lasting solar cells – keeping them cool, even in the blistering heat of the noonday sun.
Photovoltaic solar cells are among the most promising and widely used renewable energy technologies on the market today. Though readily available and easily manufactured, even the best designs convert only a fraction of the energy they receive from the sun into usable electricity. Part of this loss is the unavoidable consequence of converting sunlight into electricity. A surprisingly vexing amount, however, is due to solar cells overheating.
Under normal operating conditions, solar cells can easily reach temperatures of 130 degrees Fahrenheit (55 degrees Celsius) or more. These harsh conditions quickly sap efficiency and can markedly shorten the lifespan of a solar cell. Actively cooling solar cells, however – either by ventilation or coolants – would be prohibitively expensive and at odds with the need to optimize exposure to the sun.
The newly proposed design avoids these problems by taking a more elegant, passive approach to cooling. By embedding tiny pyramid- and cone-shaped structures on an incredibly thin layer of silica glass, the researchers found a way of redirecting unwanted heat arriving in the form of infrared radiation from the surface of solar cells, through the atmosphere, and back into space.
“Our new approach can lower the operating temperature of solar cells passively, improving energy conversion efficiency significantly and increasing the life expectancy of solar cells,” said Linxiao Zhu, a physicist at Stanford and lead author on the Optica paper. “These two benefits should enable the continued success and adoption of solar cell technology.”
Solar cells work by directly converting the sun’s rays into electrical energy. As photons of light pass into the semiconductor regions of the solar cells, they knock off electrons from the atoms, allowing electricity to flow freely, creating a current. The most successful and widely used designs, silicon semiconductors, however, convert less than 30 percent of the energy they receive from the sun into electricity – even at peak efficiency.
The solar energy that is not converted generates waste heat, which inexorably lessens a solar cell’s performance. For every one-degree Celsius (1.8 degree F) increase in temperature, the efficiency of a solar cell declines by about half a percent.
“That decline is very significant,” said Aaswath Raman, a postdoctoral scholar at Stanford and co-author on the paper. “The solar cell industry invests significant amounts of capital to generate improvements in efficiency. Our method of carefully altering the layers that cover and enclose the solar cell can improve the efficiency of any underlying solar cell. This makes the design particularly relevant and important.”
Additionally, solar cells “age” more rapidly when their temperatures increase, with the rate of aging doubling for every increase of 18 degrees Fahrenheit.
To passively cool the solar cells, allowing them to give off excess heat without spending energy doing so, requires exploiting the basic properties of light as well as a special infrared “window” through Earth’s atmosphere.
Different wavelengths of light interact with solar cells in very different ways – with visible light being the most efficient at generating electricity while infrared is more efficient at carrying heat. Different wavelengths also bend and refract differently, depending on the type and shape of the material they pass through.
The researchers harnessed these basic principles to allow visible light to pass through the added silica layer unimpeded while enhancing the amount of energy that is able to be carried away from the solar cells at thermal wavelengths.
“Silica is transparent to visible light, but it is also possible to fine-tune how it bends and refracts light of very specific wavelengths,” said Fan, who is the corresponding author on the Optica paper. “A carefully designed layer of silica would not degrade the performance of the solar cell but it would enhance radiation at the predetermined thermal wavelengths to send the solar cell’s heat away more effectively.”
To test their idea, the researchers compared two different silica covering designs: one a flat surface approximately 5 millimeters thick and the other a thinner layer covered with pyramids and micro-cones just a few microns (one-thousandth of a millimeter) thick in any dimension. The size of these features was essential. By precisely controlling the width and height of the pyramids and micro-cones, they could be tuned to refract and redirect only the unwanted infrared wavelengths away from the solar cell and back out into space.
“The goal was to lower the operating temperature of the solar cell while maintaining its solar absorption,” said Fan. “We were quite pleased to see that while the flat layer of silica provided some passive cooling, the patterned layer of silica considerably outperforms the 5 mm-thick uniform silica design, and has nearly identical performance as the ideal scheme.”
Zhu and his colleagues are currently fabricating these devices and performing experimental tests on their design. Their next step is to demonstrate radiative cooling of solar cells in an outdoor environment. “We think that this work addresses an important technological problem in the operation and optimization of solar cells,” he concluded, “and thus has substantial commercialization potential.”
This is worthwhile good news. Most photovoltaic buyers aren’t aware of the lifespan of their new cells. If nothing else should this technology get to market the importance of cell longevity will have a more prominent role in photovoltaic selection.