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April 22, 2015
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By:
Whitney Campbell
Earth Day Turns 45
Ever since Earth Day was first celebrated in 1970, the event has adapted to the environmental issues of the times.
During its inaugural year, 20 million people across the U.S. attended teach-ins and learned about the quality of the nation's water. Months earlier, coastal Santa Barbara had experienced an oil spill, while Time photographs had brought the fires of Ohio's Cuyahoga River to the country's attention. The teach-ins prompted widespread awareness of the pollution, and within the year, the Environmental Protection Agency (EPA) was formed. Passage of the Clean Water Act followed in 1972.
Growing up in the ‘80s, I remember my Earth Days being filled with VHS tapes about acid rain and "Save the Rainforest!" craft projects. I watched commercials about cutting off the lights and 3-2-1 Contact episodes about the ozone layer. In my college years, these activities turned into attending films about seed patents and lectures on the Greenhouse Gas Effect.
On this Earth Day, for me, the event still seems to be about climate change. Global warming is happening, and there's plenty of evidence to indicate this reality, from rapidly heating oceans to nutritionally depleted food chains. Its anthropogenic sources seem evident — the NASA model featured below, representing a year's worth of CO2 emissions, clearly shows the global north pumping out plumes of the gas.
Yet, despite now being an ideal moment to discuss our warming planet, state governments recently have been censoring all mentions of the predicament.
Last month, whistleblowers admitted that Florida's governor, Rick Scott, has prohibited Department of Environmental Protection officials from using the terms "climate change" or "global warming."1 A few weeks ago, in Wisconsin, the Board of Commissioners of Public Lands voted 2-to-1 to ban all work on or discussions about manmade climate disruption.2 Although these states are exposed to the effects of global warming, their officials are now prohibited from even mentioning the term.
But at the same time these discussions are being outlawed in capitol buildings, scientists are pursuing solutions in the lab. Since the emergence of these censorship measures, for example, researchers have announced the development of an artificial photosynthetic device that can trap carbon dioxide emissions and transform the CO2 into useful chemicals with solar power.3 The innovative hybrid design aims to both tackle current levels of CO2 and offer alternatives to fossil fuel-derived products.
Amidst a setting of silence on vital environmental issues, scientific breakthroughs like this can speak volumes. After the Montreal Protocol phased out chlorofluorocarbons (CFCs) globally in 1989, more than a quarter of a century passed before the ozone layer showed signs of recovery.4 On this Earth Day, a day of awareness, it's important to remember that our response to climate change will require ingenuity and persistence, and that this begins with joining together and talking about the planet's challenges.
Media credit: High-resolution computer model of carbon dioxide emissions in the atmosphere was created and made available by NASA Goddard.
1. Korten, T. "In Florida, Officials Ban Term ‘Climate Change.'" Florida Center for Investigative Reporting. March 8, 2015.
2. Hayes, C. "WI Agency Bans Mention of Climate Change." MSNBC. April 9, 2015.
3. Liu C, Gallagher JJ, Sakimoto KK, Nichols EM, Chang CJ, Chang MC, & Yang P (2015). Nanowire-Bacteria Hybrids for Unassisted Solar Carbon Dioxide Fixation to Value-Added Chemicals. Nano Letters PMID: 25848808
4. Sullivan, G. "Earth's Ozone Layer is Recovering." The Washington Post. September 11, 2014.
April 24, 2014
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By:
Whitney Campbell
Quantum Dots Open Way For Solar Windowpanes
Recently scientists at Los Alamos National Laboratory and the University of Milano-Bicocca showed how, some day with the same surface, we may be able to see the sun and glean it too. By redesigning a light-grabbing nanocrystal, these material researchers devised a technique that could change sheer Plexiglas sheets into large-area solar concentrators.1
Their innovation involves a special type of nanocrystal called a quantum dot. Varying in size from about 2 to 50 nanometers, quantum dots are made of semiconducting materials that can accept photons and convert them into electricity at substantial rates.2 Moreover, the size of each quantum dot determines the wavelength it emits, giving these nanocrystals a tuneability that scientists can use to produce an array of colors for a range of applications.
In terms of solar research, the dots' quantum mechanical properties also allow a single photon to excite two or more electrons, a phenomenon known as multiple exciton generation that results in higher yields. Theoretically, photovoltaic (PV) cells could then store this amplified charge, and the whole device could serve as a replenishable energy source.
With this potential, quantum dots could be huge for solar technology, but scaled-up designs have suffered from reabsorption problems that have limited their effectiveness. The issue dealt with the dots' absorption bands, which enter an excited state when receiving photons that's only relieved when nearby emission bands release photons in turn. In previous quantum dot prototypes, there was an overlap between the dimensions of the emission and absorption bands, such that the photons from the emission bands — that were meant to be captured by PV cells — were being soaked up again by the absorption bands instead.
The Los Alamos and UNIMIB labs worked around this constraint by engineering the absorption and emission bands from slightly different materials. They thought this structure would stagger the respective bandgaps, ensuring that the photons released by the emission bands had less energy than the photons accepted by the absorption bands, a difference called a Stokes shift. The goal was to create a big enough Stokes shift so that the absorption bands wouldn't reabsorb the photons released by the emissions bands, letting PV cells grab these packets of energy.
The Los Alamos scientists first created a "giant quantum dot" from a wide outer layer of cadmium sulfide (CdS) and a narrow core of cadmium selenide (CdSe). With this structure, the CdS casing would operate as the energy-absorber and the CdSe core as the energy-emitter, with giant in this context meaning ~10 nanometers across. The UNIMIB lab then integrated these CdSe/CdS quantum dots into slabs of almost transparent polymethylmethacrylate (PMMA) measured in the tens of centimeters.
The outcome was a luminescent solar concentrator that exhibited nearly zero losses from photon reabsorption. Additionally, in experiments with simulated solar radiation, the prototype was able to capture >10% of the total photons possible — a rate that had one researcher likening it to a "light-harvesting antennae."3
Later versions could have even larger surface areas and remain nearly transparent, making CdSe/CdS-quantum dots an ideal candidate for the development of solar windowpanes and other dynamic technologies. These advances could substantially reduce the impact of commercial and residential buildings by transitioning them off the power grid, a timely move in light of the Intergovernmental Panel on Climate Change's (IPCC) latest analysis.
According to the IPCC's most recent report,4 the building sector is a relatively small contributor of greenhouse gas (GHG) emissions, releasing only 6.4% of all GHG direct emissions in 2010, but it was the largest end-consumer of total energy that year, being responsible for 32% of final energy use.5 Relatedly, the energy supply sector was the single biggest contributor of GHG direct emissions, releasing a quarter of all GHG direct emissions that year.
In other words, while energy production was recognized as the sector most urgently needing decarbonization, buildings were the top end users of the electricity and heat being generated by GHG-gushing suppliers.
Quantum dot devices could allow buildings to be more self-sustaining and affect climate change through lowering their energy demands. From this perspective, quantum dot windowpanes could present a clearer view of what to expect from tomorrow's construction materials, as well.
Image credit: Photo of pippettes containing solutions of an array of quantum dots from the Flickr creative commons of Argonne National Laboratory.
1. Meinardi, F., Colombo, A., Velizhanin, K., Simonutti, R., Lorenzon, M., Beverina, L., Viswanatha, R., Klimov, V., & Brovelli, S. (2014). Large-area luminescent solar concentrators based on ‘Stokes-shift-engineered' nanocrystals in a mass-polymerized PMMA matrix. Nature Photonics DOI: 10.1038/nphoton.2014.54
2. Semonin, O., Luther, J., Choi, S., Chen, H., Gao, J., Nozik, A., & Beard, M. (2011). Peak External Photocurrent Quantum Efficiency Exceeding 100% via MEG in a Quantum Dot Solar Cell. Science, 334, 1530-1533 DOI: 10.1126/science.1209845
3. Press Release, Los Alamos National Laboratory. "Shiny Quantum Dots Brighten Future of Solar Cells." April 14, 2014.
4. IPCC, 2014: Summary for Policymakers. In: Climate Change 2014 Mitigation Of Climate Change. Contribution Of Working Group III To The Fifth Assessment Report Of The Intergovernmental Panel On Climate Change. Pages 7, 24 - 29. April 12, 2014.
5. The sectors of industry and transport were a close second and third, though, with the industry sector accounting for 28% of final energy use in 2010, and transport for 27%. [IPCC, 2014, Ibid].
February 13, 2014
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By:
Whitney Campbell
Lithium-Ion Batteries Get A Boost
After lithium-ion batteries were introduced to the public in the early 1990s, they've charged all kinds of products, from handheld cell phones to jumbo airplanes. But as their prevalence has grown, so have concerns with their safety.
In January 2013, airlines had to ground their fleets of Boeing Dreamliners due to fires linked to the "thermal runaway" of lithium-ion batteries. Likewise, lithium-ion-powered cars, such as the Tesla Model S, have caught fire "20 or so [times] in the past few years," sparking damaging viral videos (but still paling in comparison to the number of fires related to standard engines).1 Even more recently, a US teen's iPhone ignited in her back pocket because of its li-ion battery, an event the Daily Mail dutifully covered.
Possibly stopping more news flashes like these, this week in PNAS researchers described a design that addresses the flammability flaw.2 Rather than using the fire-prone alkyl carbonate electrolytes that most lithium-ion batteries employ, the team invented a nonflammable electrolyte with a class of compounds named the perfluoropolyethers, or PFPEs.
PFPEs have been applied as a lubricant for industrial machinery, but were being looked into as a way to prevent marine life from sticking to the bottom of ships. During this process, UNC-Chapel Hill researcher Joseph DeSimone noticed that the compound resembled in chemical structure an electrolyte already being investigated for lithium-ion devices.3
When he and his team demonstrated that PFPEs could also dissolve lithium salts, they proceeded to build a novel lithium-ion prototype, and with promising results. Tests have shown the battery to have a transference number — a measure of performance — of more than double that of conventional electrolytes.4 The prototype is stable above 200°C (~392°F) as well, making it a safer and more reliable design for larger-scale projects.
Moreover, it's not just the electrolyte-side of the battery, the part that carries the charge, that's lately been improved. Last month, University of Limerick researchers announced that they've built a better anode too, a part that the drives the charge.5
To do this, instead of working with the graphite most lithium-ion batteries use today, the team incorporated an element with a higher capacity, germanium. As this element tends to expand and shrink greatly during cycles, becoming increasingly brittle, the team intervened at the nano level to offset this characteristic. Specifically, they made an anode out of germanium standing nanowires, which restructured over time to form a "stable porous material" capable of withstanding more than 1,000 charging cycles.6
Taken together, these papers illuminate the potential of lithium-ion batteries and indicate that they can be durable, nonflammable, and energy-efficient. These advances could not only expand the horizon for electric cars, but also could lay the groundwork for lithium-ion power grids able to hold large stores of solar and wind energy without flaring up or falling apart.
Image credit: Photo of lithium-ion batteries from the Flickr stream of Argonne National Laboratory, a research hub in the US.
1. Bello, D. "Should Battery Fires Drive Electric Cars Off the Road?" Scientific American. November 12, 2013.
2. Wong, D. H. C., Thelen, J. L., Fu, Y., Devaux, D., Pandya, A. A., Battaglia, V. S., Balsara, N. P., and DeSimone, J. M. (2014). Nonflammable perfluoropolyether-based electrolytes for lithium batteries. PNAS DOI: 10.1073/pnas.1314615111
3. "Team Builds Nonflammable Lithium-Ion Battery." Phys.org. February 10, 2014.
4. Wong, et al., Ibid.
5. Kennedy, T., Mullane, E., Geaney, H., Osiak, M., O'Dwyer, C., Ryan, K. M. (2014). High-performance germanium nanowire-based lithium-Ion battery anodes extending over 1000 cycles through in situ formation of a continuous porous network. Nano Letters, 14, 716-723 PMID: 24417719
6. "Researchers Make Breakthrough in Battery Technology." R&D Magazine. February 10, 2014.
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