University of California – Irvine (UCI) researchers have devised a new way of recycling millions of tons of plastic garbage into liquid fuel. Its an egregious problem worldwide. University of California, Irvine and the Shanghai Institute of Organic Chemistry (SIOC) in China collaborated in the research.
UCI chemist Zhibin Guan explained, “Synthetic plastics are a fundamental part of modern life, but our use of them in large volume has created serious environmental problems. Our goal through this research was to address the issue of plastic pollution as well as achieving a beneficial outcome of creating a new source of liquid fuel.”
Guan and Zheng Huang, his collaborator at SIOC, together with their colleagues have figured out how to break down the strong bonds of polyethylene, the most common commercially available form of plastic. Their innovative technique centers on the use of alkanes, specific types of hydrocarbon molecules, to scramble and separate polymer molecules into other useful compounds.
Scientists have been seeking to recycle plastic bags, bottles and other trash generated by humans with less toxic or energy intensive methods. Current approaches include using caustic chemicals known as radicals or heating the material to more than 700º Fahrenheit to break down the chemical bonds of the polymers.
In this newly discovered technique, the team degrades plastics in a milder and more efficient manner through a process known as cross-alkane metathesis. The substances needed for the new method are byproducts of oil refining, so they’re readily available.
Guan said the U.S.-China joint team is still working on a few issues to make it more efficient. That includes increasing the catalyst activity and lifetime, decreasing the cost, and developing catalytic processes to turn other plastic trash into useful products.
Waste plastic is a very big problem that shows up in every home, business, landfill and out at sea. The team is on to something that one dearly hopes is a worthwhile long term solution. Trash for fuel. Sign me up.
Gwangju Institute of Science and Technology scientists in South Korea have made ultra-thin photovoltaics flexible enough to wrap around the average pencil. The flexible solar cells could power wearable electronics like fitness trackers and smart glasses.
Thin materials flex more easily than thick ones – think of a piece of paper versus a cardboard shipping box. The reason for the difference: The stress in a material while it’s being bent increases farther out from the central plane. Because thick sheets have more material farther out they are harder to bend.
Jongho Lee, an engineer at the Gwangju Institute said, “Our photovoltaic is about 1 micrometer thick”. One micrometer is much thinner than an average human hair. Standard photovoltaics are usually hundreds of times thicker, and even most other thin photovoltaics are 2 to 4 times thicker.
The institute’s researchers made the ultra-thin solar cells from the common semiconductor gallium arsenide. They stamped the cells directly onto a flexible substrate without using an adhesive that would add to the material’s thickness. The cells were then “cold welded” to the electrode on the substrate by applying pressure at 170 degrees Celcius and melting a top layer of material called photoresist that acted as a temporary adhesive. The photoresist was later peeled away, leaving the direct metal to metal bond.
The metal bottom layer also served as a reflector to direct stray photons back to the solar cells. The researchers tested the efficiency of the device at converting sunlight to electricity and found that it was comparable to similar thicker photovoltaics. They performed bending tests and found the cells could wrap around a radius as small as 1.4 millimeters.
The team also performed numerical analysis of the cells, finding that they experience one-fourth the amount of strain of similar cells that are 3.5 micrometers thick.
“The thinner cells are less fragile under bending, but perform similarly or even slightly better,” Lee said.
A few other groups have reported solar cells with thicknesses of around 1 micrometer, but have produced the cells in different ways, for example by removing the whole substract by etching.
By transfer printing instead of etching, the new method developed by Lee and his colleagues may be used to make very flexible photovoltaics with a smaller amount of materials.
Lee said the thin cells can be integrated onto eyeglass frames or fabric and might power the next wave of wearable electronics such as the new fitbit monitoring devices.
Now integrated circuits do more and use less power and the improvements will keep coming. This solar concept may not be ready now for fully powering devices, but could well have a very useful role in extending the time between charges.
June 21, 2016 | 1 Comment
Lawrence Livermore National Laboratory (LLNL) scientists have combined biology and 3-D printing to create the first reactor that can continuously produce methanol from methane at room temperature and pressure.
The team removed enzymes from methanotrophs, bacteria that eat methane, and mixed them with polymers that they printed or molded into innovative reactors.
The invention could lead to more efficient conversion to methane for energy production. Methane production may become a very practical bio fuel product, especially if it can economically be reformed and condensed into a liquid fuel, such as methanol.
The invention is packed with potential.
Sarah Baker, LLNL chemist and project lead said, “Remarkably, the enzymes retain up to 100 percent activity in the polymer. The printed enzyme-embedded polymer is highly flexible for future development and should be useful in a wide range of applications, especially those involving gas-liquid reactions.” The comment suggests that the current working invention could be a base for a new field.
Advances in oil and gas extraction techniques have made vast new stores of natural gas, composed primarily of methane, available. However, a large volume of methane is leaked, vented or flared during these operations, partly because the gas is difficult to store and transport compared to more-valuable liquid fuels. Methane emissions also contribute about one-third of current net global warming potential, primarily from these and other distributed sources such as agriculture and landfills.
Current industrial technologies to convert methane to more valuable products, like steam reformation, operate at high temperature and pressure, require a large number of unit operations and yield a range of products. As a result, current industrial technologies have a low efficiency of methane conversion to final products and can only operate economically at very large scales.
A technology to efficiently convert methane to other hydrocarbons is needed as a profitable way to convert “stranded” sources of methane and natural gas (sources that are small, temporary, or not close to a pipeline) to liquids for further processing, the team reported.
The only known catalyst (industrial or biological) to convert methane to methanol under ambient conditions with high efficiency is the enzyme methane monooxygenase (MMO), which converts methane to methanol. The reaction can be carried out by methanotrophs that contain the enzyme, but this approach inevitably requires energy for upkeep and metabolism of the organisms. Instead, the team separated the enzymes from the organism and used the enzymes directly.
The team found that the isolated enzymes offer the promise of highly controlled reactions at ambient conditions with higher conversion efficiency and greater flexibility.
“Up to now, most industrial bioreactors are stirred tanks, which are inefficient for gas-liquid reactions,” said Joshuah Stolaroff, an environmental scientist on the team. “The concept of printing enzymes into a robust polymer structure opens the door for new kinds of reactors with much higher throughput and lower energy use.”
The team found that the 3-D-printed polymer could be reused over many cycles and used in higher concentrations than possible with the conventional approach of the enzyme dispersed in solution.
At this writing natural gas is cheap, really cheap, so much of the potential won’t be realized for some time. But the government has chosen natural gas to kill out coal use which will surely drive the price of natural gas higher. The next time the natural gas supply comes up short lets hope there are tanks of methanol waiting to fill in the shortfall.
On the other side of the world scientists at Hong Kong Polytechnic University report they have successfully developed perovskite-silicon tandem solar cells with the world’s highest power conversion efficiency of 25.5%.
First a look at the Swiss effort where Michael Graetzel and his team found that, by briefly reducing the pressure while fabricating perovskite crystals, they were able to achieve the highest performance ever measured for larger-size perovskite solar cells, reaching over 20% efficiency and matching the performance of conventional thin-film solar cells of similar sizes. The Swiss team’s results have been published in Science.
While this is promising news for perovskite technology that is already low cost and under industrial development, the high performance in pervoskites does not necessarily herald the doom of silicon-based solar technology. Safety issues still need to be addressed regarding the lead content of current perovskite solar-cell prototypes in addition to determining the stability of actual devices.
The layering perovskites on top of silicon to make hybrid solar panels may actually boost the silicon solar-cell industry. Efficiency could exceed 30%, with the theoretical limit being around 44%. The improved performance would come from harnessing more solar energy: the higher energy light would be absorbed by the perovskite top layer, while lower energy sunlight passing through the perovskite would be absorbed by the silicon layer.
Graetzel is known for his transparent dye-sensitized solar cells. It turns out that the first perovskite solar cells were dye-sensitized cells where the dye was replaced by small perovskite particles. His lab’s latest perovskite prototype, roughly the size of an SD memory card, looks like a piece of glass that is darkened on one side by a thin film of perovskite. Unlike the transparent dye-sensitized cells, the perovskite solar cell is opaque.
Meanwhile in Hong Kong the scientists report they have successfully developed perovskite-silicon tandem solar cells with the world’s highest power conversion efficiency of 25.5%.
The research team in the Department of Electronic and Information Engineering led by Professor Charles Chee Surya, Clarea Au Endowed Professor in Energy, has recently made this world record with innovative means to enhance energy conversion efficiency. With this innovation, it is estimated that solar energy can be generated at cost of HK$2.73/W, compared with HK$3.9/W at present generated by existing silicon solar cells available in the market.
Because there are different wavelengths for solar energy, a combination of different materials for making solar cells would work best for energy absorption. For example, methylammonium lead tri-halide perovskite and silicon solar cells can form a complementary pair. With the perovskite solar cell functioning as a top layer, it can harvest the short wavelength photons while the bottom layer coated with silicon is designed to absorb the long wavelength photons.
PolyU’s research team maximizes efficiency by making use of this feature with three innovative approaches. Firstly, the team discovered a chemical process – low-temperature annealing process in dry oxygen to reduce the impact made by perovskite defects. Secondly, the team fabricated a tri-layer of molybdenum trioxide / gold / molybdenum trioxide with optimized thickness of each layer, making it highly transparent for light to go into the bottom silicon layer under perovskite layer.
Finally, by mimicking the surface morphology of the rose petals, a haze film, developed by Dr Zijian Zheng of PolyU Institute of Textiles and Clothing, was applied as the top layer of the solar panel to trap more light. All three innovative approaches help enhance energy conversion efficiency.
Professor Shen Hui of Sun Yat-sen University and Shun De SYSU Institute for Solar Energy, who excelled in the fabrication high-efficiency silicon cells, was responsible for the design and fabrication of the bottom silicon cell.
The folks in Hong Kong are on a roll with a lab prototype testing.
But don’t count the Swiss out.
Perovskite solar cells first appeared in 2009 with an efficiency of just 3.8%. With the outstanding photovoltaic properties, perovskite solar cell has become a subject of vigorous research for sustainable power generation, with researchers around the world finding new ways to increase its energy conversion efficiency. It has currently established itself as one of the most promising solar cell materials.
To make a perovskite solar cell, the scientists must grow crystals that have a special structure, called “perovskite” after Russian mineralogist Lev Perovski who discovered it.
The scientists first dissolve a selection of compounds in a liquid to make some “ink.” They then place the ink on a special type of glass that can conduct electricity. The ink dries up, leaving behind a thin film that crystallizes on top of the glass when mild heat is applied. The end result is a thin layer of perovskite crystals.
The tricky part is growing a thin film of perovskite crystals so that the resulting solar cell absorbs a maximum amount of light. Scientists are constantly looking for smooth and regular layers of perovskite with large crystal grain size in order to increase photovoltaic yields.
One example is spinning the cell when the ink is still wet flattening the ink and wicking off some of the excess liquid, leading to more regular films. A new vacuum flash technique used by Graetzel and his team also selectively removes the volatile component of this excess liquid. At the same time, the burst of vacuum flash creates seeds for crystal formation, leading to very regular and shiny perovskite crystals of high electronic quality.
Both of these teams are progressing with quite a bit of quality in the material performance. The numbers are looking good. There is still that lurking lead issue, but as more experience is gained and more creativity and innovation comes in, perovskite will get not just better, but commercially viable as well.
June 15, 2016 | 1 Comment
Los Alamos National Lab (LANL) scientists used water doped with hydrazine in a transition metal dichalcogenides electrocatalyst. The new concept presents one of the best hydrogen water splitting electrocatalyst processes to date and also opens up a whole new direction for research in electrochemistry and semiconductor device physics.
The LANL scientists are working on understanding how to use a simple, room-temperature treatment to drastically change the properties of materials that may well lead to a revolution in renewable fuels production and electronic applications.
Its actually a spectacular development in the hydrogen field. No precious metals involved.
Gautam Gupta, project leader at Los Alamos National Laboratory in the Light to Energy team of the Lab’s Materials Synthesis and Integrated Devices group said, “We demonstrate in our study that a simple chemical treatment, in this case a drop of dilute hydrazine (N2H4) in water, can dope electrons directly to a semiconductor, creating one of the best hydrogen-evolution electrocatalysts.”
The press release explains, “In the 2015 movie ‘The Martian,’ stranded astronaut Matt Damon turns to the chemistry of rocket fuel, hydrazine and hydrogen, to create lifesaving water and nearly blows himself up. But if you turn the process around and get the hydrazine to help, you create hydrogen from water by changing conductivity in a semiconductor, a transformation with wide potential applications in energy and electronics.”
In recent years, the materials science community has grown more interested in the electrical and catalytic properties of layered transition metal dichalcogenides (TMDs). TMDs are primarily metal sulfides and selenides (e.g., MoS2) with a layered structure, similar to graphite; this layered structure allows for unique opportunities, and challenges, in modifying electrical properties and functionality.
Gupta and Aditya Mohite, a physicist with a doctorate in electrical engineering, have been pioneering work at Los Alamos seeking to understand the electrical properties of TMDs and use that knowledge to optimize these semiconductors for renewable fuels production.
In this work, MoS2 shell — MoOx core nanowires, as well as pure MoS2 particles and 2D sheets — are tested for electrocatalysis of the hydrogen evolution reaction. The addition of dilute hydrazine to MoS2 significantly improves the electrocatalytic performance. Further characterization shows that the MoS2 changes from semiconducting behavior to having more metallic properties following the hydrazine exposure.
“The most interesting thing about this result is that it is different than conventional doping, where actual chemicals are added to a semiconductor to change its charge carrier concentration. In the case of hydrazine treatment, we are ‘doping’ electrons directly to the material, without modifying the original chemistry,” said Dustin Cummins, first author on this project, currently a postdoctoral researcher in the Laboratory’s Sigma Division working on the DOE/NNSA CONVERT Program exploring fuel fabrication for next-generation reactors.
Cummins first found the hydrogen-production result working with Gupta at Los Alamos as a graduate student research affiliate from the University of Louisville (advisor: Dr. Mahendra Sunkara) and he continued to conduct experiments and refine discussion while working as a postdoc.
“Hydrazine acting as an electron dopant in inorganic semiconductors has been observed since the 1970s, but there is limited understanding of the process,” Cummins noted. “Our biggest hurdle was to prove to that hydrazine was actually changing the conductivity of the MoS2 system, and that is what results in increased catalytic activity,” which was demonstrated on single-flake devices, he said.
Multiple areas of Los Alamos staff expertise in layered semiconductors, chemistry, spectroscopy, electrical device fabrication and more all came together to provide some of the best understanding and mechanism to date for hydrazine acting as an electron dopant.
Gupta discussed the paper saying, This paper, “Efficient Hydrogen Evolution in Transition Metal Dichalcogenides via a Simple One-Step Hydrazine Reaction,” not only presents one of the best hydrogen water splitting electrocatalysts to date, but also “it opens up a whole new direction for research in electrochemistry and semiconductor device physics in general.”
This technology is on its way. The team said, “For commercialization and technologically viable use of TMDs for hydrogen production, thermal stability and long-term durability are required.” The technology isn’t ready yet, but the potential in cutting the costs of freeing hydrogen for fuel use is huge. Its an effort worthy of congratulations and more encouragement.