Converting atmospheric carbon dioxide into batteries

An interdisciplinary team of scientists has worked out a way to make electric vehicles that are not only carbon neutral, but carbon negative, capable of actually reducing the amount of atmospheric carbon dioxide as they operate.

They have done so by demonstrating how the graphite electrodes used in the lithium-ion batteries that power electric automobiles can be replaced with carbon material recovered from the atmosphere.

The recipe for converting carbon dioxide gas into batteries is described in the paper titled "Carbon Nanotubes Produced from Ambient Carbon Dioxide for Environmentally Sustainable Lithium-Ion and Sodium-Ion Battery Anodes" published in the Mar. 2 issue of the journal ACS Central Science.

The unusual pairing of carbon dioxide conversion and advanced battery technology is the result of a collaboration between the laboratory of Assistant Professor of Mechanical Engineering Cary Pint at Vanderbilt University and Professor of Chemistry Stuart Licht at George Washington University.

The team adapted a solar-powered process that converts carbon dioxide into carbon so that it produces carbon nanotubes and demonstrated that the nanotubes can be incorporated into both lithium-ion batteries like those used in electric vehicles and electronic devices and low-cost sodium-ion batteries under development for large-scale applications, such as the electric grid.

"This approach not only produces better batteries but it also establishes a value for carbon dioxide recovered from the atmosphere that is associated with the end-user battery cost unlike most efforts to reuse CO2 that are aimed at low-valued fuels, like methanol, that cannot justify the cost required to produce them," said Pint.

The project builds upon a solar thermal electrochemical process (STEP) that can create carbon nanofibers from ambient carbon dioxide developed by the Licht group and described in the journal Nano Letters last August. STEP uses solar energy to provide both the electrical and thermal energy necessary to break down carbon dioxide into carbon and oxygen and to produce carbon nanotubes that are stable, flexible, conductive and stronger than steel.

"Our climate change solution is two fold: (1) to transform the greenhouse gas carbon dioxide into valuable products and (2) to provide greenhouse gas emission-free alternatives to today's industrial and transportation fossil fuel processes," said Licht. "In addition to better batteries other applications for the carbon nanotubes include carbon composites for strong, lightweight construction materials, sports equipment and car, truck and airplane bodies."

 

Joining forces with Pint, whose research interests are focused on using carbon nanomaterials for battery applications, the two laboratories worked together to show that the multi-walled carbon nanotubes produced by the process can serve as the positive electrode in both lithium-ion and sodium-ion batteries.

In lithium-ion batteries, the nanotubes replace the carbon anode used in commercial batteries. The team demonstrated that the carbon nanotubes gave a small boost to the performance, which was amplified when the battery was charged quickly. In sodium-ion batteries, the researchers found that small defects in the carbon, which can be tuned using STEP, can unlock stable storage performance over 3.5 times above that of sodium-ion batteries with graphite electrodes. Most importantly, both carbon-nanotube batteries were exposed to about 2.5 months of continuous charging and discharging and showed no sign of fatigue.

Depending on the specifications, making one of the two electrodes out of carbon nanotubes means that up to 40 percent of a battery could be made out of recycled CO2, Pint estimated. This does not include the outer protective packaging but he suggested that processes like STEP could eventually produce the packaging as well.

The researchers estimate that with a battery cost of $325 per kWh (the average cost of lithium-ion batteries reported by the Department of Energy in 2013), a kilogram of carbon dioxide has a value of about $18 as a battery material - six times more than when it is converted to methanol - a number that only increases when moving from large batteries used in electric vehicles to the smaller batteries used in electronics. And unlike methanol, combining batteries with solar cells provides renewable power with zero greenhouse emissions, which is needed to put an end to the current carbon cycle that threatens future global sustainability.

Licht also proposed that the STEP process could be coupled to a natural gas powered electrical generator. The generator would provide electricity, heat and a concentrated source of carbon dioxide that would boost the performance of the STEP process. At the same time, the oxygen released in the process could be piped back to the generator where it would boost the generator's combustion efficiency to compensate for the amount of electricity that the STEP process consumes. The end result could be a fossil fuel electrical power plant with zero net CO2 emissions.

"Imagine a world where every new electric vehicle or grid-scale battery installation would not only enable us to overcome the environmental sins of our past, but also provide a step toward a sustainable future for our children," said Pint. "Our efforts have shown a path to achieve such a future."

Vanderbilt University

Nanostructured germanium for portable photovoltaics and battery electrodes

New approaches for hybrid solar cells

 

Using a new procedure researchers at the Technical University of Munich (TUM) and the Ludwig Maximillians University of Munich (LMU) can now produce extremely thin and robust, yet highly porous semiconductor layers. A very promising material – for small, light-weight, flexible solar cells, for example, or electrodes improving the performance of rechargeable batteries.

The coating on the wafer that Professor Thomas Fässler, chair of Inorganic Chemistry with a Focus on Novel Materials at TU Munich, holds in his hands glitters like an opal. And it has amazing properties: It is hard as a crystal, exceptionally thin and – since it is highly porous – light as a feather.

By integrating suitable organic polymers into the pores of the material, the scientists can custom tailor the electrical properties of the ensuing hybrid material. The design not only saves space, it also creates large interface surfaces that improve overall effectiveness.

“You can imagine our raw material as a porous scaffold with a structure akin to a honeycomb. The walls comprise inorganic, semiconducting germanium, which can produce and store electric charges. Since the honeycomb walls are extremely thin, charges can flow along short paths,” explains Fässler.

The new design: bottom-up instead of top-down

But, to transform brittle, hard germanium into a flexible and porous layer the researchers had to apply a few tricks. Traditionally, etching processes are used to structure the surface of germanium. However, this top-down approach is difficult to control on an atomic level. The new procedure solves this problem.

Together with his team, Fässler established a synthesis methodology to fabricate the desired structures very precisely and reproducibly. The raw material is germanium with atoms arranged in clusters of nine. Since these clusters are electrically charged, they repel each other as long as they are dissolved. Netting only takes place when the solvent is evaporated.

This can be easily achieved by applying heat of 500 °C or it can be chemically induced, by adding germanium chloride, for example. By using other chlorides like phosphorous chloride the germanium structures can be easily doped. This allows the researchers to directly adjust the properties of the resulting nanomaterials in a very targeted manner.

Tiny synthetic beads as nanotemplates

To give the germanium clusters the desired porous structure, the LMU researcher Dr. Dina Fattakhova-Rohlfing has developed a methodology to enable nanostructuring: Tiny polymer beads form three-dimensional templates in an initial step.

In the next step, the germanium-cluster solution fills the gaps between the beads. As soon as stable germanium networks have formed on the surface of the tiny beads, the templates are removed by applying heat. What remains is the highly porous nanofilm.

The deployed polymer beads have a diameter of 50 to 200 nanometers and form an opal structure. The germanium scaffold that emerges on the surface acts as a negative mold – an inverse opal structure is formed. Thus, the nanolayers glitter like an opal.

“The porous germanium alone has unique optical and electrical properties that many energy relevant applications can profit from,” says LMU researcher Dr. Dina Fattakhova-Rohlfing, who, in collaboration with Fässler, developed the material. “Beyond that, we can fill the pores with a wide variety of functional materials, thereby creating a broad range of novel hybrid materials.”

Nanolayers pave the road to portable photovoltaic solutions

“When combined with polymers, porous germanium structures are suitable for the development of a new generation of stable, extremely light-weight and flexible solar cells that can charge mobile phones, cameras and laptops while on the road,” explains the physicist Peter Müller-Buschbaum, professor of functional materials at TU Munich.

Manufacturers around the world are on the lookout for light-weight and robust materials to use in portable solar cells. To date they have used primarily organic compounds, which are sensitive and have relatively short lifetimes. Heat and light decompose the polymers and cause the performance to degrade. Here, the thin but robust germanium hybrid layers provide a real alternative.

Nanolayers for new battery systems

Next, the researchers want to use the new technology to manufacture highly porous silicon layers. The layers are currently being tested as anodes for rechargeable batteries. They could conceivably replace the graphite layers currently used in batteries to improve their capacity.

The research was funded by the “Solar Technologies Go Hybrid” program of the Bavarian State Ministry of Science, in the context of the excellence cluster “Nanosystems Initiative Munich (NIM), the German Research Foundation (DFG) and the Center for Nanosciences (CeNS).

Publication:

Zintl Clusters as Wet Chemical Precursors for Germanium Nanomorphologies with Tunable Composition; Manuel M. Bentlohner, Markus Waibel, Patrick Zeller, Kuhu Sarkar, Peter Müller-Buschbaum, Dina Fattakhova-Rohlfing, Thomas F. Fässler
Angewandte Chemie, online 03.12.2015 – DOI: 10.1002/ange.201508246

Technical University of Munich

http://www.nanotechnologyworld.org/?draft=true#!Nanostructured-germanium-for-portable-photovoltaics-and-battery-electrodes/c89r/56659a740cf28314431b0321 

New plastic solar cell minimizes loss of photon energy

A Japanese research team demonstrates an unconventional means to achieve more efficient and robust conversion of solar energy into electricity

As the world increasingly looks to alternative sources of energy, inexpensive and environmentally friendly polymer-based solar cells have attracted significant attention, but they still do not match the power harvest of their more expensive silicon-based counterparts.

Now, researchers at the RIKEN Center for Emergent Matter Science and Kyoto University's Department of Polymer Chemistry have shown that a newly developed polymer can minimize energy loss as well as silicon-based solar cells when converting photon energy from sunlight to electricity.

Solar cells work because photons from the sun strike electrons and move them into a position where they can create an electric current. Photon energy loss -- the amount of energy lost when converting photons energy from sunlight into electric power -- was greater in polymer-based solar cells than in silicon-based ones.

"In polymer-based plastic solar cells, larger photon energy loss causes lower voltage. This has been one of the largest limiting factors for efficiency," explains Hideo Ohkita, one of the authors of the study, which was published in the Dec. 2, 2015 issue of Nature Communications. "The new polymer has the potential to lead to a breakthrough on this issue."

The group began working with the new polymer, where oxygen rather than sulfur atoms are located at key positions, and found that the new material was able to overcome some of the key obstacles to extracting and utilizing greater energy from sunlight.

"Since this new polymer greatly reduces photon energy loss, it has allowed us to achieve a superb power conversion efficiency of nearly 9% with a very high open-circuit voltage in plastic solar cells," explains Itaru Osaka.

An efficiency of 15% is usually seen as a breakthrough level that will allow polymer-based cells to be commercialized.

"By achieving both a high short-circuit current and a high open-circuit voltage," he continues, "achieving a power conversion efficiency of 15% in single-junction cells is a realistic goal. This would have huge implications for the solar energy sector."

The paper 'High-efficiency polymer solar cells with small photon energy loss' appeared Dec. 2, 2015 in Nature Communications, with doi: 10.1038/ncomms10085

Kyoto University

Discovery Creates a Better Chance for Clean Energy Research

This is a magnified image of a new thermoelectric 

material discovered by University of Houston researchers.

Credit: University of Houston

UH Researchers Find First New High-Efficiency Thermoelectric Material in 60 Years

University of Houston physicists have discovered a new thermoelectric material offering high performance at temperatures ranging from room temperature up to 300 degrees Celsius, or about 573 degrees Fahrenheit.

“This new material is better than the traditional material, Bismuth telluride, and can be used for waste heat conversion into electricity much more efficiently,” said Zhifeng Ren, M.D. Anderson Chair professor of physics at UH and the lead author of a paper describing the discovery, published online by Nano Energy.

Ren, who is also principal investigator at the Texas Center for Superconductivity at UH, said the work could be important for clean energy research and commercialization at temperatures of about 300 degrees Celsius.

Bismuth telluride has been the standard thermoelectric material since the 1950s and is used primarily for cooling, although it can also be used at temperatures up to 250 C, or 482 F, for power generation, with limited efficiency.

For this discovery, Ren and other members of his lab used a combination of magnesium, silver and antimony to generate electricity from heat using the thermoelectric principle. They added a small amount of nickel, after which Ren said the compound worked even better.

The work was done in collaboration with researchers from the UH Department of Chemistry and the Massachusetts Institute of Technology. Huaizhou Zhao and Jiehe Sui, a member of Ren’s lab whose home institute is the Harbin Institute of Technology in China, were primary contributors; Zhao is now a research scientist at the Institute of Physics with the Chinese Academy of Sciences.

The material works well up to 300 C, Ren said; work to improve its efficiency is ongoing.

The potential for capturing heat – from power plants, industrial smokestacks and even vehicle tailpipes – and converting it into electricity is huge, allowing heat that is currently wasted to be used to generate power. Ren said temperatures there can range from 200 C to 1,000 C, and until now, there hasn’t been a thermoelectric material capable of working once conditions get beyond the lower levels of heat. Much of the demand ranges from 250 C to 300 C, he said.

Ren long has worked in thermoelectrics, among other scientific fields. His research group published an article in the journal Science in 2008 establishing that the efficiency – the technical term is the “figure of merit” – of Bismuth telluride could be increased as much as 20 percent by changing how it is processed. At the time, Ren was at Boston College.  

And his lab last summer published a paper in the Proceedings of the National Academy of Sciences establishing tin telluride with the addition of the chemical element indium as a material capable of converting waste heat to electricity. But tin telluride works best at temperatures higher than about 300 C, or about 573 F, making it important to continue looking for another material that works at lower temperatures.

Ren’s group isn’t the first to study the new material, which has not been named but is referred to in the Nano Energy paper as simply MgAgSb-based materials, using the chemical names for the elements used to create it. The paper cites work done in 2012 by M.J. Kirkham, et al; that work used magnesium, silver and antimony in equal parts, Ren said, but resulted in impurities and poor conducting properties.  

He said his lab found that using slightly less silver and antimony, and mixing the elements separately – putting magnesium and silver first in the ball milling process, adding the antimony after several hours – eliminated the impurities and significantly improved the thermoelectric properties.

“We had much different qualities,” he said. “Better, with no impurities, and smaller grain size, along with much better thermoelectric properties.”

http://www.uh.edu/news-events/stories/2014/May/0507RenThermoelectrics.php