University of Illinois at Chicago researchers have determined how electrocatalysts can convert carbon dioxide to carbon monoxide using water and electricity. The discovery can lead to the development of efficient electrocatalysts for large scale production of synthesis gas – a mixture of carbon monoxide and hydrogen.

Reduction of CO2 With Water and Electricity Graphic. Image Credit: University of Illinois at Chicago. Click image for the largest view.

Meenesh Singh, assistant professor of chemical engineering and lead author on the study published in the journal Proceedings of the National Academy of Sciences said, “The electrochemical reduction of carbon dioxide to fuels is a subject of considerable interest because it offers a means for storing electricity from energy sources such as wind and solar radiation in the form of chemical bonds.”

During his postdoctoral research at the University of California, Berkeley, Singh studied artificial photosynthesis and was part of a team that developed artificial leaves that, when exposed to direct sunlight, were capable of converting carbon dioxide to fuels.

In his latest research, Singh developed a state-of-the-art multiscale model that unites a quantum-chemical analysis of reaction pathway; a microkinetic model of the reaction dynamics; and a continuum model for transport of species in the electrolyte to learn precisely how carbon dioxide can be electrochemically reduced through a catalyst, in this case silver, and made into carbon monoxide.

While the most plausible reaction pathway is usually identified from quantum-chemical calculation of the lowest free-energy pathway, this approach can be misleading when coverages of adsorbed species differ significantly, Singh said. It is essential, therefore, to integrate the effects from electronic states of a catalyst at the atomic-level with the dynamics of species in the electrolyte at the continuum-level for accurate prediction of electrocatalytic reaction pathways.

Singh pointed out, “This multiscale model is one of the biggest accomplishments in electrochemistry.”

To understand how electrocatalysts in fuel cells or electrochemical cells work, scientists need to first probe the electronic and quantum levels, which can be extremely challenging in the presence of an electric field, said Jason Goodpaster, assistant professor of chemistry at the University of Minnesota and one of the co-authors. It took Singh and Goodpaster more than one year to individually produce and benchmark the models and integrate them into a multiscale framework for full-scale simulation of the electrochemical reaction.

This is the first time, Singh said, that scientists have predicted quantitatively from first principles, the current density of carbon monoxide and hydrogen as a function of applied potential and pressure of carbon dioxide.

“Once you recognize how these reactions are occurring on electrocatalysts, you can control the catalysts structure and operating conditions to produce carbon monoxide efficiently,” Singh said. Since they are product gases – carbon monoxide and hydrogen are insoluble in aqueous electrolytes – they can be readily separated as synthesis gas and converted into fuels such as methanol, dimethyl ether, or a mixture of hydrocarbons.

Electrocatalysts such as gold, silver, zinc, palladium and gallium are known to yield mixtures of carbon dioxide and hydrogen at various ratios depending on the applied voltage, Singh said. Gold and silver exhibit the highest activity towards carbon dioxide reduction, and since silver is more abundant and less expensive than gold, “silver is the more promising electrocatalyst for large-scale production of carbon monoxide,” he said.

It will be interesting to see which, if any, of the CO2 recycling ideas can justify sequestering CO2 from effluents. Its likely that the successful one can be operated efficiently in the flue gas environment. Its usually a warm flow of quite a variety of chemical gases and small particulates. There’s a long way to go from simulations to a catalyst making a living uprating CO2.

Northwestern University researchers have discovered with a series of theoretical simulations, that surface polarization in mixed media increases attraction among rare earth elements.

Despite their name, rare earth elements actually aren’t that rare. Abundant in mines around the world, rare earths are used in many high-tech products, including visual displays, batteries, super conductors, and computer hard drives. But while they aren’t necessarily tricky to find, the elements often occur together and are extremely difficult to separate and extract.

Northwestern University’s Monica Olvera de la Cruz explained the problem with, “Having the ability to recover rare earths is important because they are finite but in high demand. To extract them, we need them to disperse and separate, but they tend to aggregate and clump together.”

Ions Of Rare Earth Inside Water Droplets In Refining. Image Credit: Northwestern University. Click image for the largest view.

Olvera de la Cruz and her team are working to better understand why rare earths are strongly attracted to each other across long distances, making separation and extraction tediously difficult. A series of molecular simulations suggest, for the first time, that the medium in which the elements are suspended – in addition to the elements themselves – is partially responsible for the strong attraction. This finding could potentially make rare earth recovery faster, easier, and less expensive.

Sponsored by the US Department of Energy, the research was recently published in Physical Review Letters. Meng Shen, a postdoctoral fellow in Olvera de la Cruz’s laboratory, served as the paper’s first author, with graduate student Honghao Li who also contributed to the work.

Rare earths are a set of 17 chemical elements along the bottom of the periodic table. Because most of the elements each have +3 charges in their ionic structures, they are notoriously difficult to separate.

Olvera de la Cruz, the Lawyer Taylor Professor of Materials Science and Engineering in Northwestern’s McCormick School of Engineering explained further, “They become very concentrated. If we could understand why they attract one another, we could optimize the extraction mechanism.”

The time-consuming and expensive separation process requires hundreds of steps and toxic chemical solvents. To separate the elements, engineers encapsulate them in self-assembled nanodroplets of water immersed in oil. Engineers then use surfactants, which grab the elements from the water and pull them into the oil. But when the water droplets are suspended in oil, the droplets are strongly attracted to one another and aggregate.

“Earlier experiments and full-atom calculations revealed that these droplets interact strongly at all large distances,” Shen said. “Unfortunately, those studies did not reveal the origin of those interactions.”

In a theoretical study, Olvera de la Cruz’s team discovered that the mixed medium of oil and water plays a major role.

“A unique feature of these emulsions is that the interface between the two mediums gives rise to surface polarization,” Olvera de la Cruz explained. “That surface polarization contributes to the inter-droplet interactions.”

“We thought that the polarization of the induced charge would make a minor contribution to the interaction,” Shen said. “But we found that the induced charge of the surface polarization actually makes a major contribution to the interaction.”

Although researchers have previously studied charged nanoparticles in water, they typically used fixed, step-by-step approaches that did not apply to such a dynamic system. Olvera de la Cruz bypassed this issue by developing a computational approach.

“The charge of the droplets is determined by the polarization, and the polarization is determined by the charge,” she said. “We developed a technique that could determine charge polarization and the response of the medium simultaneously.”

The most noteworthy result, the team also discovered that the finding only applies to water droplets in oil. When the reverse occurs – oil droplets suspended in water – the induced charge is repulsive and the attraction is reduced. This better understanding of emulsions can be applied to separating rare earths as well as other elements, including the removal of radioactive metals and nuclear waste.

This is very welcome work. Much of the progress from consumer and industrial products depends on reare earths getting less costly. One hopes the Northwestern team’s work translates quickly into industrial processing savings.

University of Liverpool researchers have made a significant breakthrough in the direct conversion of carbon dioxide (CO2) and methane (CH4) into liquid fuels and chemicals which could help industry to reduce greenhouse gas emissions while producing valuable chemical feedstocks. Or, its recycling some of the CO2. Its a very interesting catalytic process.

In a paper published in chemistry journal Angewandte Chemie they report a very unique plasma synthesis process for the direct, one-step activation of carbon dioxide and methane into higher value liquid fuels and chemicals (e.g. acetic acid, methanol, ethanol and formaldehyde) with high selectivity at ambient conditions of room temperature and atmospheric pressure.

This is the first time this process has been shown, as it is a significant challenge to directly convert these two stable and inert molecules into liquid fuels or chemicals using any single-step conventional (e.g. catalysis) processes bypassing high temperature, energy intensive syngas production process and high pressure syngas processing for chemical synthesis.

Direct and indirect processes for the conversion of CO2 and CH4 into liquid fuels and chemicals. Image Credit: University of Liverpool. Click image for the largest view.

The one-step room-temperature synthesis of liquid fuels and chemicals from the direct reforming of CO2 with CH4 was achieved by using a novel atmospheric-pressure non-thermal plasma reactor with a water electrode and a low energy input.

Dr. Xin Tu, from the University’s Department of Electrical Engineering and Electronics, said, “These results clearly show that non-thermal plasmas offer a promising solution to overcome the thermodynamic barrier for the direct transformation of CH4 and CO2 into a range of strategically important platform chemicals and synthetic fuels at ambient conditions. Introducing a catalyst into the plasma chemical process, known as plasma-catalysis, could tune the selectivity of target chemicals. ”

“This is a major breakthrough technology that has great potential to deliver a step-change in future methane activation, CO2 conversion and utilization and chemical energy storage, which is also of huge relevance to the energy & chemical industry and could help to tackle the challenges of global warming and greenhouse gas effect,” he added.

Plasma, the fourth state of matter, an electrically charged gas mixture, offers a promising and attractive alternative for the synthesis of fuels and chemicals, providing a unique way to enable thermodynamically unfavorable reactions to take place at ambient conditions.

In non-thermal plasmas, the gas temperature remains low (as low as room temperature), while the electrons are highly energetic with a typical electron temperature of 1-10 eV, which is sufficient to activate inert molecules (e.g. CO2 and CH4) present and produce a variety of chemically reactive species including radicals, excited atoms, molecules and ions. These energetic species, which are produced at a relatively low temperature, are capable of initiating a variety of different reactions.

Plasma systems have the flexibility to be scaled up and down. In addition, high reaction rate and fast attainment of steady state in a plasma process allows rapid start-up and shutdown of the plasma process compared to other thermal processes, which significantly reduces the overall energy cost and offers a promising route for the plasma process powered by renewable energy (e.g. wind and solar power) to act as an efficient chemical energy storage localized or distributed system.

The highly attractive process could also provide a promising solution to end gas flaring from oil and gas wells through the conversion of flared methane into valuable liquid fuels and chemicals which can be easily stored and transported. Around 3.5% (~150 billion cubic meter gas) of the world’s natural-gas supply was wastefully burned, or ‘flared’, at oil and gas fields, emitting more than 350 million tons of CO2.

This is a very interesting breakout from conventional thinking. Aside from the incessant references to global warming, which the authors seem to have missed the many discrediting studies and dishonesty revelations, this work has value of its own merits and is sure to be taken up and expanded upon by others. The independent oil and gas companies are anxious to find economically valid ways to not flare off the cash value of methane. The trick will be to come up with the free CO2.

Georgia Institute of Technology researchers have developed a paper-based flexible supercapacitor using a simple layer-by-layer coating technique that could be used to help power wearable devices. The device uses metallic nanoparticles to coat cellulose fibers in the paper, creating supercapacitor electrodes with high energy and power densities – and the best performance so far in a textile-based supercapacitor.

By implanting conductive and charge storage materials in the paper, the technique creates large surface areas that function as current collectors and nanoparticle reservoirs for the electrodes. Testing shows that devices fabricated with the technique can be folded thousands of times without affecting conductivity.

Image shows that the flexible metallized paper developed in this research retains its conducting properties even when crumpled and folded. Image Credit: Ko et al, Georgia Tech.

Seung Woo Lee, an assistant professor in the Woodruff School of Mechanical Engineering at the Georgia Institute of Technology said, “This type of flexible energy storage device could provide unique opportunities for connectivity among wearable and internet of things devices. We could support an evolution of the most advanced portable electronics. We also have an opportunity to combine this supercapacitor with energy-harvesting devices that could power biomedical sensors, consumer and military electronics, and similar applications.”

The research, done with collaborators at Korea University, was supported by the National Research Foundation of Korea and reported September 14 in the journal Nature Communications.

Energy storage devices are generally judged on three properties: their energy density, power density and cycling stability. Supercapacitors often have high power density, but low energy density – the amount of energy that can be stored – compared to batteries, which often have the opposite attributes. In developing their new technique, Lee and collaborator Jinhan Cho from the Department of Chemical and Biological Engineering at Korea University set out to boost energy density of the supercapacitors while maintaining their high power output.

The researchers began by dipping paper samples into a beaker of solution containing an amine surfactant material designed to bind the gold nanoparticles to the paper. Next they dipped the paper into a solution containing gold nanoparticles. Because the fibers are porous, the surfactants and nanoparticles enter the fibers and become strongly attached, creating a conformal coating on each fiber.

By repeating the dipping steps, the researchers created a conductive paper on which they added alternating layers of metal oxide energy storage materials such as manganese oxide. The ligand-mediated layer-by-layer approach helped minimize the contact resistance between neighboring metal and/or metal oxide nanonparticles. Using the simple process done at room temperatures, the layers can be built up to provide the desired electrical properties.

“It’s basically a very simple process,” Lee said. “The layer-by-layer process, which we did in alternating beakers, provides a good conformal coating on the cellulose fibers. We can fold the resulting metallized paper and otherwise flex it without damage to the conductivity.”

Though the research involved small samples of paper, the solution-based technique could likely be scaled up using larger tanks or even a spray-on technique. “There should be no limitation on the size of the samples that we could produce,” Lee said. “We just need to establish the optimal layer thickness that provides good conductivity while minimizing the use of the nanoparticles to optimize the tradeoff between cost and performance.”

The researchers demonstrated that their self-assembly technique improves several aspects of the paper supercapacitor, including its areal performance, an important factor for measuring flexible energy-storage electrodes. The maximum power and energy density of the metallic paper-based supercapacitors are estimated to be 15.1mW cm2 and 267.3 Wh cm2, respectively, substantially outperforming conventional paper or textile supercapacitors.

The next steps will include testing the technique on flexible fabrics, and developing flexible batteries that could work with the supercapacitors. The researchers used gold nanoparticles because they are easy to work with, but plan to test less expensive metals such as silver and copper to reduce the cost.

During his Ph.D. work, Lee developed the layer-by-layer self-assembly process for energy storage using different materials. With his Korean collaborators, he saw a new opportunity to apply that to flexible and wearable devices with nanoparticles.

“We have nanoscale control over the coating applied to the paper,” he added. “If we increase the number of layers, the performance continues to increase. And it’s all based on ordinary paper.”

The desire and demands for more electrical energy storage continues with gathering intensity. This technology may offer a very cost effective solution, but only for a time as the demand will increase in any case. The technology is still in the lab, but this team has a very short list to cover before trying for going up in scale. Good Luck team, we’re rooting for you.

Brookhaven National Laboratory chemists have designed a new ‘single-site’ catalyst that speeds up the rate of a key step in artificial photosynthesis. It’s the first to match the efficiency of the catalytic sites that drive this reaction in nature and could greatly improve the potential for making efficient solar-to-fuel conversion devices.

The new catalyst has a ruthenium (Ru) atom at its core, a “pendant” phosphonate group to act as a base that accepts protons (H+) from water, and a more flexible, or “labile,” carboxylate group that facilitates the interaction of the catalyst with water.. Image Credit: Brookhaven National Lab. Click image for the largest view.

The chemistry is about an effort to mimic how plants, algae, and some bacteria harness sunlight to convert water and carbon dioxide into energy-rich fuels. This step, called water oxidation, releases protons and electrons from water molecules, producing oxygen as a byproduct.

David Shaffer, a Brookhaven research associate and lead author on a paper describing the work in the Journal of the American Chemical Society said, “The end goal is to break out those molecular building blocks – the protons and electrons – to make fuels such as hydrogen. The more efficient the water oxidation cycle is, the more energy we can store.”

But breaking apart water molecules isn’t easy.

Brookhaven chemist Javier Concepcion, who led the research team pointed out, “Water is very stable. Water can undergo many boiling/condensing cycles and it stays as H2O. To get the protons and electrons out, we need to make the water molecules react with each other.”

The catalyst acts as a chemical handler, shuffling around the water molecules’ assets – electrons, hydrogen ions (protons), and oxygen atoms – to get the reaction to happen.

The new catalyst design builds on one the group developed last year, led by graduate student Yan Xie, which was also a single-site catalyst, with all the components needed for the reaction on a single molecule. This approach is attractive because the scientists can optimize how the various parts are arranged so that reacting molecules come together in just the right way. Such catalysts don’t depend on the free diffusion of molecules in a solution to achieve reactions, so they tend to continue functioning even when fixed to a surface, as they would be in real-world devices.

Concepcion said, “We used computer modeling to study the reactions at the theoretical level to help us design our molecules. From the calculations we have an idea of what will work or not, which saves time before we get into the lab.”

In both Xie’s design and the new improvement, there’s a metal at the core of the molecule, surrounded by other components the scientists can choose to give the catalyst particular properties. The reaction starts by oxidizing the metal, which pulls electrons away from the oxygen on a water molecule. That leaves behind a “positively charged,” or “activated,” oxygen and two positively charged hydrogens (protons).

“Taking electrons away makes the protons easier to release. But you need those protons to go somewhere. And it’s more efficient if you remove the electrons and protons at the same time to prevent the build-up of excess charges,” Concepcion said. “So Xie added phosphonate groups as ligands on the metal to act as a base that would accept those protons,” he explained. Those phosphonate groups also made it easier to oxidize the metal to remove the electrons in the first place.

But there was still a problem. In order to activate the H2O molecule, you first need it to bind to the metal atom at the center of the catalyst.

In the first design, the phosphonate groups were so strongly bound to the metal that they were preventing the water molecule from binding to the catalyst early enough to keep the process running smoothly. That slowed the catalytic cycle down.

So the team made a substitution. They kept one phosphonate group to act as the base, but swapped out the other for a less-tightly-bound carboxylate.

Shaffer said, “The carboxylate group can more easily adjust its coordination to the metal center to allow the water molecule to come in and react at an earlier stage.”

“When we are trying to design better catalysts, we first try to figure out what is the slowest step. Then we redesign the catalyst to make that step faster,” he said. “Yan’s work made one step faster, and that made one of the other steps end up being the slowest step. So in the current work we accelerated that second step while keeping the first one fast.”

The improvement transformed a catalyst that created two or three oxygen molecules per second to one that produces more than 100 per second – with a corresponding increase in the production of protons and electrons that can be used to create hydrogen fuel.

“That’s a rate that is comparable to the rate of this reaction in natural photosynthesis, per catalytic site,” Concepcion said. “The natural photosynthesis catalyst has four metal centers and ours only has one,” he explained. “But the natural system is very complex with thousands and thousands of atoms. It would be extremely hard to replicate something like that in the lab. This is a single molecule and it does the same function as that very complex system.”

The next step is to test the new catalyst in devices incorporating electrodes and other components for converting the protons and electrons to hydrogen fuel – and then later, with light-absorbing compounds to provide energy to drive the whole reaction.

“We have now systems that are working quite well, so we are very hopeful,” Concepcion said.

This is quite the catalytic innovation with great promise. While still a lab build up, there does seem to be reason to think there ay be good prospects for this type of technology. There remains the issue of scaling up after producing hydrogen and solar powering. And out there still, is the matter of economics. But when the fossil fuel era winds down there looks to be great confidence building that there will be fuels for the future.


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