Chinese team develop fuel cell that can clean water as it generates electricity

Yanbiao Liu and his colleagues from Shanghai Jiao Tong University, have succeeded in building a device capable of both cleaning wastewater and producing electricity from it. Using light as an energy source the team created a photo-catalytic fuel cell that used a titanium dioxide nanotube-array anode and a cathode based on platinum. The light energy degrades the organic material found in the wastewater and in the process generates electrons which pass through the cathode converting it into electricity. The team has published its results on Water Science & Technology.

Liu notes in the paper, that wastewater (the stuff that goes down the toilet when flushed) or sewage, as it’s more commonly known in other countries, is a great source of environmental pollution and at the same time, is a truly important and often overlooked source of energy, which, unfortunately generally is not collected and used. It’s also an expensive by-product of human existence. Every day billions of people contribute to the ever growing problem of what to do with all the human waste that is created.

In addition to organic material, wastewater often contains other materials that need to be removed in order to reuse the water for other purposes. In their lab the team tested their fuel cell’s ability to separate clear aromatics (perfumes), azo dyes, pharmaceuticals, personal care products and endocrine-disrupting compounds (birth control pill chemicals that wind up in urine) from wastewater samples and found they were able to separate them completely from the organic material thus producing clean water.

To allow the system to use visible and regular sunlight rather than UV, the team modified the electrodes with semiconductors (such as CdS) which means of course the system, if industrialized, could be used outside as an add-on perhaps to existing wastewater treatment plants.
So far the team hasn’t listed cost estimates for building an electrical/wastewater treatment facility with their new technology, but it’s not hard to see how useful such a plant would be in areas where sewage is sometimes not treated at all, but simply dumped into rivers or streams, or worse, in the streets. In addition to helping clean up such places, the people in those areas would benefit from the electricity that would be produced in the process.

More information: A TiO2-nanotube-array-based photocatalytic fuel cell using refractory organic compounds as substrates for electricity generation, Chem. Commun., 2011, Advance Article, DOI: 10.1039/C1CC13388H

Abstract
A TiO2-nanotube-array-based photocatalytic fuel cell system was established for generation of electricity from various refractory organic compounds and simultaneous wastewater treatment. The present system can respond to visible light and produce obviously enhanced cell performance when a narrow band-gap semiconductor (i.e. Cu2O and CdS) was combined with TiO2 nanotubes.

 

A new set of building blocks for simple synthesis of complex molecules

Assembling chemicals can be like putting together a puzzle. University of Illinois chemists have developed a way of fitting the pieces together to more efficiently build complex molecules, beginning with a powerful and promising antioxidant.

Led by chemistry professor Martin Burke, the team published its research on the cover of the chemistry journal Angewandte Chemie.

Burke's group is known for developing a synthesis technique called iterative cross-coupling (ICC) that uses simple, stable chemical "building blocks" sequentially joined in a repetitive reaction. With more than 75 of the building blocks available commercially, pharmaceutical companies and other laboratories use ICC to create complex small molecules that could have medicinal properties.

"There's pre-installed functionality and stereochemistry, so everything is set in the building blocks, and all you have to do is couple them together," said graduate student Seiko Fujii, the first author of the paper.

However, ICC has been limited to only molecules with one type of polarity. Now, the group has developed reverse-polarity ICC, which allows a chemist to optimize the ICC process to match the target molecules' electronic structure. The reversal in polarity enables a whole new class of building blocks, so researchers can synthesize molecules more efficiently and even construct molecules that standard ICC cannot.

For example, in the paper, the group used the new method to make synechoxanthin (pronounced sin-ecko-ZAN-thin), a molecule first isolated from bacteria in 2008 that shows great promise as an antioxidant. Studies suggest that synechoxanthin allows the bacteria that produce it to live and thrive in highly oxidative environments.

"We as humans experience a lot of oxidative stress, and it can be really deleterious to human health," said Burke, who also is affiliated with the Howard Hughes Medical Institute. "It can lead to diseases like cancer and atherosclerosis and neurodegenerative disorders. Evidence strongly suggests that synechoxanthin is a major part of the bacteria's solution to this problem. We're excited to ask the question, what can we learn from the bug? Can it also protect a human cell?"

Studies on the activity of synechoxanthin have been limited by the difficulty of extracting the molecule from bacterial cultures. Burke's group successfully synthesized it from a mere three types of readily available, highly stable, non-toxic building blocks. Thanks to the ease of ICC, they can produce relatively large quantities of synechoxanthin for study as well as derivatives to test against the natural product.

"Because this building-block-based design is inherently flexible, once we've made the natural product, we can make any derivative we want simply by swapping in one different building block, and then using the reverse-polarity ICC to snap them together," Burke said. "That's where synthesis is so powerful. Oftentimes, the cleanest experiment will require a molecule that doesn't exist, unless you can piece it together."

Researchers can also use blocks that have been "tagged" with a fluorescent or radioactive dye to make it easier to study the molecule and its activity. For example, Fujii next plans to synthesize both synechoxanthin and its apolar derivative with tags so that NMR imaging can reveal its location and orientation within a cell's membrane, possibly providing clues to its activity.

"After we have all these molecules in hand, we're really excited to test the antioxidant activity of them in a model membrane," Fujii said.

Provided by University of Illinois at Urbana-Champaign (news : web)

New rechargeable batteries needed: A microporous polymer is an unusually powerful supercapacitor

 For future electric vehicles, powerful notebook computers, and other portable devices, we need a new generation of energy storage materials that are better suited to modern needs than current rechargeable batteries. The best materials for this are known as supercapacitors. A team led by Dinglin Jiang at the National Institutes of Natural Sciences in Okazaki (Japan) has now introduced a new material with outstanding supercapacitor properties in the journal Angewandte Chemie.

Emission-free electric cars are well suited for drives around the city; for long stretches, however, this has not been the case. The problem stems from the small amount of energy that can be stored, which covers only short distances before requiring a charge, and the amount of current that can be delivered, which limits the speed and acceleration of the vehicles. Supercapacitors could overcome these challenges because they combine the advantages of earlier capacitors and batteries: like a capacitor, they can deliver high current densities on demand while storing a large amount of electric energy like a battery.

Supercapacitors work on a different charge-storage principle than rechargeable batteries, and consist of electrochemical double layers on electrodes, which are wetted by an electrolyte. When a voltage is applied, ions of opposite charge collect on both electrodes to form wafer-thin zones of immobilized charge carriers. In contrast to a battery, there is only a shift of charge; no chemical transformation occurs. Various materials are suitable for supercapacitors, but the truly perfect material has yet to be found. The researchers in Japan have now reached an important milestone along the way.

There is one class of materials with interesting properties: special microporous, framework-like, organic polymers. Their double bonds are arranged in such a way that some of their electrons can move freely over extended regions of the framework as an “electron cloud”. Such materials are thus conducting. A large inner surface area is important for the formation of electrostatic charge-separation layers in the pores. Jiang and his team have now synthesized a nitrogen-containing framework with a pore size optimal for allowing ions to flow in and out rapidly – a requirement for rapid charging and discharging. The nitrogen centers interact with the electrolyte ions, thus favoring the accumulation of charge and the movement of ions.

The interplay between these different advantageous properties provides the new material with an unusually high charge storage capacity and high energy density. Jiang and his co-workers were able to demonstrate that their microporous frameworks can withstand many charge/discharge cycles.

More information: Donglin Jiang, Supercapacitive Energy Storage and Electric Power Supply Using an Aza-Fused ?-Conjugated Microporous Framework, Angewandte Chemie International Edition, http://dx.doi.org/ … ie.201103493

Provided by Wiley (news : web)

Faster organic semiconductors for flexible displays can be developed quickly with new method

 Organic semiconductors hold immense promise for use in thin film and flexible displays – picture an iPad you can roll up – but they haven’t yet reached the speeds needed to drive high definition displays. Inorganic materials such as silicon are fast and durable, but don’t bend, so the search for a fast, durable organic semiconductor continues.

Now a team led by researchers at Stanford and Harvard universities has developed a new organic semiconductor material that is among the speediest yet. The scientists also accelerated the development process by using a predictive approach that lopped many months – and could lop years – off the typical timeline. 

For the most part, developing a new organic electronic material has been a time-intensive, somewhat hit-or-miss process, requiring researchers to synthesize large numbers of candidate materials and then test them.

The Stanford and Harvard-led group decided to try a computational predictive approach to substantially narrow the field of candidates before expending the time and energy to make any of them.

“Synthesizing some of these compounds can take years,” said Anatoliy Sokolov, a postdoctoral researcher in chemical engineering at Stanford, who worked on synthesizing the material the team eventually settled on.  “It is not a simple thing to do.”

Sokolov works in the laboratory of Zhenan Bao, an associate professor of chemical engineering at Stanford.  They are among the authors of a paper describing the work, published in the Aug. 16 issue of Nature Communications.  Alán Aspuru-Guzik, an associate professor of chemistry and chemical biology at Harvard, led the research group there and directed the theory and computation efforts.

The researchers used a material known as DNTT, which had already been shown to be a good organic semiconductor, as their starting point, then considered various compounds possessing chemical and electrical properties that seemed likely to enhance the parent material’s performance if they were attached.

They came up with seven promising candidates.

Semiconductors are all about moving an electrical charge from one place to another as fast as possible.  How well a material performs that task is determined by how easy is it for a charge to hop onto the material and how easily that charge can move from one molecule to another within the material.

Using the expected chemical and structural properties of the modified materials, the Harvard team predicted that two of the seven candidates would most readily accept a charge.  They calculated that one of those two was markedly faster in passing that charge from molecule to molecule, so that became their choice. From their analysis, they expected the new material to be about twice as fast as its parent.

Sokolov, the Stanford researcher, said it took about a year and a half to perfect the synthesis of the new compound and make enough of it to test. “Our final yield from what we produced was something like 3 percent usable material and then we still had to purify it.”

When the team members tested the final product, their predictions were borne out. The modified material doubled the speed of the parent material.  For comparison, the new material is more than 30 times faster than the amorphous silicon currently used for liquid crystal displays in products such as flat panel televisions and computer monitors. 

“It would have taken several years to both synthesize and characterize all the seven candidate compounds. With this approach, we were able to focus on the most promising candidate with the best performance, as predicted by theory,” Bao said. "This is a rare example of truly 'rational' design of new high performance materials.”

The researchers hope their predictive approach can serve as a blueprint for other research groups working to find a better material for organic semiconductors. 

And they’re eager to apply their method to the development of new, high-efficiency material for organic solar cells.

"In the case of renewable energy, we have no time for synthesizing all the possible candidates, we need theory to complement synthetic approaches to accelerate materials discovery,” said Aspuru-Guzik.

Other Stanford researchers contributing to the research include Rajib Mondal and Hylke Akkerman, postdoctoral fellows in the department of chemical engineering when the research was done; Stefan Mannsfeld, a staff scientist at the Stanford Synchrotron Radiation Lightsource; and Arjan Zoombelt, a postdoctoral fellow in chemical engineering.

Provided by Stanford University (news : web)