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Nitrogen Can Triple Energy Capacity of Supercapacitors

Nitrogen can triple the energy storage capacity of carbon-based supercapacitors, researchers in China and the United States say, potentially helping make them competitive against some advanced batteries.

Supercapacitors can capture and release energy much more quickly than batteries, but they usually can store less energy. Most supercapacitors in use today use carbon-based electrodes, because their high-surface area stores more charge. "We are able to make carbon a much better supercapacitor," says Fuqiang Huang, a material chemist at the Shanghai Institute of Ceramics.

The scientists began with a framework of porous silica and lined the pores with carbon. They next etched away the silica, leaving porous tubes 4 to 6 nanometers wide, each made of five or less layers of graphene-like carbon.

They then doped the carbon with nitrogen atoms. The nitrogen altered the otherwise inert carbon, helping chemical reactions occur within the supercapacitor without affecting its electric conductivity.

These changes enhanced the capacitor's ability to store energy by roughly threefold without reducing its ability to quickly charge and discharge. "It is as if we have broken the sound barrier," Huang says.

The scientist say that their devices could store 41 watt-hours per kilogram, comparable to lead-acid batteries.

"A bus can run on an 8 watt-hours per kilogram supercapacitor for 5 kilometers, then recharge for 30 seconds at the depot to run on the trip again,” says I-Wei Chen, a materials physicist at the University of Pennsylvania who also worked on the breakthrough. “This works in a small city or an airport, but there is obviously a lot to be desired," he says. "Our battery has five times the energy, so it can run 25 kilometers and still charge at the same speed. We are then talking about serious applications in a serious way in transportation."

The new supercapacitor does not store as much energy as lithium-ion batteries, which achieve 70 to 250 watt-hours per kilogram. However, the researchers say their supercapacitor beats them on power. The nitrogen supercapacitor can crank out 26 kilowatts per kilogram, while lithium-ion batteries are only capable of 0.2 to 1 kilowatts per kilogram.

The scientists are now investigating ways to create these supercapacitors in a scalable, robust, and inexpensive manner, Huang says. They are also experimenting with a variety of electrolytes to further improve the energy and power of these devices.

They detailed their findings this week in in the journal Science.

Flames from burning methane, iron, aluminum, boron, and zirconium

Metal Powder: the New Zero-Carbon Fuel?

The two solid fuel boosters that burned for two minutes helping the U.S.’s old space shuttle fleet to reach its orbit each contained 80 tons of aluminum powder, which corresponds to 16 percent of the total weight of the solid fuel.  "This idea of burning metals as a fuel sounds pretty far out there, but this is something that has been done in rockets forever," says Jeffrey Bergthorson, an aeronautics engineer at McGill University in Montreal, Canada.  He and colleagues at McGill and at the European Space Agency  published this week in Applied Energy a study outlining how metal powder could serve as a zero-carbon fuel to power transportation and the grid.

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How the Paris Climate Deal Happened and Why It Matters

One month after the terror attacks that traumatized Paris, the city has produced a climate agreement that is being hailed as a massive expression of hope. On Monday the U.K. Guardian dubbed the Paris Agreement, “the world’s greatest diplomatic success.” Distant observers may be tempted to discount such effusive language as hyperbole, yet there are reasons to be optimistic that last weekend’s climate deal finally sets the world on course towards decisive mutual action against global climate change. 

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"Hydricity" Would Couple Solar Thermal and Hydrogen Power

Solar heat could help generate both electricity and hydrogen fuel at the same time in a system that scientists in Switzerland and the United States call "hydricity." Such a system could supply electricity round-the-clock with an overall efficiency better than many photovoltaic cells, researchers add.

There are two ways solar energy is used to generate electricity. Photovoltaic cells directly convert sunlight to electricity, while solar thermal power plants—also known as concentrating solar power systems—focus sunlight with mirrors, heating water and producing high-pressure steam that drives turbines.

Photovoltaic cells only absorb a portion of the solar spectrum, but they can generate electricity from both direct and diffuse sunlight. Solar thermal power plants can use more wavelengths of the solar spectrum, but they can only operate in direct sunlight, limiting them to sun-rich areas. Moreover, the highest conversion efficiencies reported yet for solar thermal power plants are significantly less than those for photovoltaic cells.

Scientists now suggest that coupling solar thermal power plants with hydrogen fuel production facilities could result in "hydricity" systems competitive with photovoltaic designs.

Today’s solar thermal power plants operate at temperatures of up to roughly 625 degrees C. However, the researchers noted that solar thermal power plants are more efficient at higher temperatures. What’s more, when they reach temperatures above 725 degrees C they can split water into it’s constituents, hydrogen and oxygen.

An integrated "hydricity" system would produce both steam for generating electricity and hydrogen for storing energy. And each makes the other more efficient. Set to produce hydrogen alone, its production efficiency approaches 50 percent, the researchers claim. This is because the high-pressure steam the system generates can easily be used to pressurize hydrogen. The substantial amount of power needed to compress hydrogen fuel for later transport and use is often neglected when it comes to calculating hydrogen production efficiency.

Furthermore, this new solar thermal energy design can generate electricity with standalone efficiencies approaching up to an unprecedented 46 percent, researchers say. This is because the high-temperature steam leaving high-pressure turbines can run a succession of lower-pressure turbines, helping make the most of the solar thermal energy the system collects.

Moreover, the hydrogen fuel the system generates can be burned to  generate electricity after nightfall, for round-the-clock power. The researchers say the efficiency of this hydrogen-to-electricity system could reach up to 70 percent, comparable to the highest reported hydrogen fuel cell efficiencies.

Altogether, the researchers say the sun-to-electricity efficiency of hydricity, averaged over a 24-hour cycle, might approach roughly 35 percent, nearly the efficiency attained using the best multijunction photovoltaic cells combined with batteries. In addition, they note that the hydrogen fuel the system produces could find use in transportation, chemical production, and other industries. Finally, unlike batteries, stored hydrogen neither discharges over time nor degrades with repeated use.

The scientists at Purdue University in West Lafayette, Ind., and the Federal Polytechnic School of Lausanne in Switzerland detailed their findings online 14 December in the journal Proceedings of the National Academy of Sciences.

Renewables Grew to 15.5% of US Electricity Capacity in 2014

Renewable electricity capacity reached 15.5% of the total installed electricity capacity in the US by the end of 2014, according to a report by the National Renewable Energy Laboratory. Installed capacity exceeded 179 gigawatts, generated 554 terawatt-hours.

NREL produced the 2014 Renewable Energy Data Book to "provide useful insights for policymakers, analysts, and investors," NREL Energy Analyst Philipp Beiter said in a statement.

The NREL team found that hydropower made up the vast majority of renewable electricity generation in 2014, followed by wind.

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Here's a Peek at the First Sodium-ion Rechargeable Battery

Lithium-ion batteries are everywhere, powering phones, cars, and avionics, among other things. However, lithium is a relatively rare element, found in some locations in South America. That not only keeps the price of lithium-ion batteries high, but also makes the supply chain vulnerable to political instabilities.  

Sodium has a very similar chemistry to lithium, and as soon as lithium-ion batteries came to market, researchers started looking to sodium as a substitute for lithium in rechargeable batteries. Unlike lithium, the reserves of sodium are practically unlimited. The highest hurdle for sodium to clear on its way to battery dominance is the development of suitable electrodes.

At the end of November a team of French researchers from the CNRS, the  French National Centre for Scientific Research and the CEA, France's Alternative Energies and Atomic Energy Commission, announced in a press release and a CNRS News article that they had produced, in collaboration with the Research Network on Electrochemical Energy Storage, RS2E, a prototype sodium-ion battery that can store an acceptable amount of electricity in the same standard industry format as lithium ion batteries. It is slightly larger than an AA battery—18 mm x 65 mm. 

Although the news article calls the composition of the negative electrode "a trade secret," the team applied for a patent in October of this year, describing a negative electrode with a layered structure based on the titanium oxide compound Na2Ti3O7, and a method to produce it.

Such electrode structures can store lithium ions, and recently researchers have begun investigating their suitability for storing sodium ions.  

"The chemistry is very close to that of the lithium battery, and from that point of view there are no major difficulties; the mechanisms are the same ones and all the industrial processes for their production are the same," says Laurence Croguennec, a material scientist at the CNRS Institut de Chimie de la Matière Condensée de Bordeaux.

One remaining problem is that sodium is less efficient as a charge carrier.  "A sodium battery loses 0.3 volts as to compared to a lithium battery. You have to develop materials that can function at higher voltages and that provide ample capacity," says Croguennec.

Whether sodium-ion batteries will reach parity with lithium-ion batteries is still an open question. "The development of the electrode has taken six months, so this gives us hope for improvement.  The performance that has been announced is quite good for a starting point, and materials can be further optimized," says Croguennec. For the moment the sodium batteries have a storage capacity of 90Wh/kg, which is comparable to the early lithium batteries.

"We are not yet close to the energy levels that you can find, for example, in Tesla cars," says Croguennec. At this point, the most reasonable application for sodium batteries is renewable energy storage, as they could be cheaper per stored unit of energy and are scalable in size like lithium batteries, explains Croguennec.

The prototypes are not yet ready for the market, but CEA believes they will be of interest to industry. “We are now in discussion with possible industrial partners, says Croguennec.

Bill Gates and Tech Billionaires Launch Clean Energy Coalition

Bill Gates will lead a coalition of billionaires and institutional investors to quicken the pace of private sector investment in clean energy.

Gates commitment to clean energy preceded the COP21 climate change conference in Paris with the announcement of the Breakthrough Energy Coalition.

Bill Gates is initially joined by Jeff Bezos, founder of Amazon, Virgin Group founder Richard Branson, Jack Ma, executive chairman of Alibaba, Mark Zuckerberg of Facebook, Ratan Tata of Tata Sons and other billionaires from 10 countries. The University of California is the sole institutional investor.

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Orion Spacecraft Ready for Major Test

In a major step towards NASA's efforts to regain the ability to send humans into space, the structural test model of the Orion spacecraft’s service module has been delivered for testing at the agency's Plum Brook Research Station in Sandusky, Ohio. The module was built by Airbus Defence and Space for the European Space Agency, representing the first time that Europe has collaborated with NASA on a project of this kind.

The European Service Module (ESM) is the powerhouse for Orion, providing its electricity and propulsion as well as carrying the air and water for the crew during voyages to the vicinity of the moon. It is based on ESA's Automated Transfer Vehicle (ATV); five ATV’s were built to supply the International Space Station and also to provide a propulsion system for altering the ISS's orbit.

Because of their towing capacity, the ATVs were frequently called Space Trucks; Orion will serve as a “Space Taxi,” taking crew to the ISS and returning them home, as the Russian Soyuz system currently does. But Orion is also the cornerstone of NASA's plans to take humans beyond low Earth orbit: in the short term, back to the Moon, with the eventual goal of journeying onwards to Mars.

While the ATV was an autonomous craft capable of flying itself and docking with the ISS, the ESM does not have its own on-board computers. It relies on the Orion Command Module for processing. This, said Oliver Junkenhofel, program manager for ESM at Airbus, has necessitated a different approach for his team: working closely with his project partners in the United States. “We have all the usual spaceflight challenges of reducing weight and certifying the systems, but we also have to handle the interfaces,” he said. “But our experiences with the ISS have been very valuable. That has proved we can work on complex, manned space projects with multiple partners, and it's a model for this work.”

While at Plum Brook, the ESM will be subjected to vibration tests to mimic the effects of the launch, and will be bombarded with intense sound waves to simulate the effects of passing through the layers of the atmosphere at supersonic speeds. (These acoustic tests will also simulate the effect of the rocket engines of the Orion abort system, which sits above the capsule and will pull it off the launch vehicle to save the crew if an emergency occurs at launch.) These tests will take about a year, and will inform the Airbus team if the module needs reinforcement as they build the flight module.

A test version of the crew module for Orion, built by prime contractor Lockheed Martin, was recently put through its paces at Plum Brook. The first model actually destined for flight is currently under construction at Lockheed's facility in Louisiana. Refining the interfaces between the command and service modules was the most challenging part of the project, according to Mike Hawes, program manager for Orion at Lockheed Martin. “We work together with Airbus as one team on this,” he said. “But ensuring that all the systems work together has been demanding.”

The first flight for Orion—an unmanned two-way trip into lunar orbit —is scheduled for 2018. ESA is currently contracted to provide the service module solely for this mission, but it already expects to supply service modules for subsequent manned missions and is planning accordingly. The space agency has been invited to bid for these subsequent projects, says ESA development head Nico Dettmann, although no final decision on the contractors is expected until early in 2016. “But as far as we're concerned in terms of planning,” says Junkenhofel, “we're part of the plan for going to Mars.” 

New Flow Battery Ups Storage Capacity by Factor of Ten

To smooth out the peaks and valleys inherent in generating electric power from the sun and the wind, utility companies want massive battery farms capable of storing the surplus energy from renewable power sources for use when the sun goes down and the wind isn’t blowing. One candidate for this application is a redox flow battery that uses liquids to store and release energy.

Redox flow batteries possess a number of features that make them attractive for large-scale energy storage for power girds. For instance, their cost per kilowatt-hour is lower than the lithium-ion batteries often used in mobile devices, and their overall energy capacity can easily be expanded by adding more fluid to match a grid's growing needs.

Heretofore, they’ve been limited by low energy density—that is, energy stored per unit volume. To offer the storage needed by a local or regional power grid, they would need a lot of space, which is often limited in the cities they are intended to power. For example, the energy density of the vanadium redox-flow battery, the most developed type of redox flow battery, is roughly one-tenth that of lithium-ion batteries.

But in a paper published in the 27 November online edition of the journal Science Advancesscientists in Singapore reported that they have developed new redox flow lithium batteries whose energy densities match those of their lithium-ion counterparts. “The energy density of redox flow lithium batteries can be about eight to 10 times as high as conventional redox flow batteries,” says Qing Wang, a materials scientist at the National University of Singapore who is a member of the team that made the breakthrough.

The key innovation: solid granules in the electrolyte tanks made from the same kinds of compounds that make up the anodes and cathodes in lithium-ion batteries. 

Previous research had explored using solid materials in redox flow batteries. But prior approaches used viscous slurries of solid materials, which can take a lot of energy to pump through a battery’s interior. The new redox flow lithium battery keeps the solid granules stationary, and only pumps the electrolytes around.

The scientists used granules of lithium iron phosphate for the cathode material and titanium dioxide for the anode material. The granules are porous, to increase the amount of surface area available for electricity-generating chemical reactions.

One challenge the scientists faced in developing this battery was fabricating the membrane separating the electrolytes. The membrane needed to possess high permeability to lithium ions, low permeability to other chemicals, and good mechanical and chemical stability. The researchers ultimately settled on a lithium-loaded composite membrane made of the commercially available electroactive polymer Nafion, which is commonly used in fuel cells, plus polyvinylidene difluoride, a tough plastic that is resistant to flame, electricity, and attack by most chemicals.

Still, says Wang, the membrane they used is not good enough for transporting lithium ions at the scale necessary for power storage applications. Future research is needed to improve the membrane and other parts of the battery before before the improved redox flow battery can be used by utilities.

Belgian Regulators Approve Restart of Flawed Reactors

Belgian nuclear authorities have authorized the restart of two reactors whose steel reactor pressure vessels (RPVs)—which contain the reactors' fissioning cores and primary coolant—are riddled with flaws. The flaws were discovered during routine maintenance in 2012. After followup ultrasonic imaging of the RPVs, experimental testing of steel samples, and extensive computational analyses, the regulators accepted the operator’s argument that the RPV flaws are decades old and do not compromise the vessels’ structural integrity.

The flaws in Belgium’s Doel 3 and Tihange 2 reactors idled the two 1,000-megawatt reactors in 2012 and again in 2014, prompting preparations for potential blackouts in Belgium and stymying European grid operators’ efforts to upgrade their system for coordinating cross-border power flows. They also prompted European regulators to call for expanded ultrasonic testing of all RPVs—a move resisted by the U.S. Nuclear Regulatory Commission.  

The Belgian reactors will take about four weeks to restart, according to World Nuclear News. There’s no word yet on whether Brussels-based reactor operator Electrabel will seek to extend the operation of Tihange 2 and Doel 3, which reach their 40-year original design lifespan in 2022 and 2023, respectively. However, regulators approved 10-year extensions for the Doel plant's two older reactors last month.

An independent structural analysis by Oak Ridge National Laboratory (ORNL) in the United States affirmed the structural integrity of the Tihange 2 and Doel 3 reactors, says Richard Bass, a corporate fellow at ORNL and coauthor of the review commissioned by Belgium's Federal Agency for Nuclear Control (FANC). “As far as we’re concerned, the flaw population meets the ASME pressure vessel requirements,” says Bass, referring to the American Society of Mechanical Engineers’ RPV codes.

ORNL, the principal contractor for the U.S. Nuclear Regulatory Commission on RPV integrity issues, applied that expertise to evaluate the safety case for the Belgian reactors put forward by Electrabel. “We had about two months total, so we did everything that we could reasonably do during that period,” says Bass. 

Bass and his colleagues examined the flaws—a total of 16,196 disc-shaped gaps detected in the RPVs' steel plates—and ran simulations meant to indicate whether the faults would initiate cracks under various stress scenarios. Simulations focused on the rapid temperature fluctuations that could happen, for example, in the case of a loss-of-coolant accident such as occurred at Fukushima Daiichi in 2011. They also projected the embrittlement of the RPV as it ages.

Of the thousands of flaws in the two reactors, four faults flunked ORNL’s initial simulations. Bass said that ORNL then accounted for the fact that the loading on the RPV would occur while it was warm, which makes the steel more robust during subsequent cooling—a metallurgical phenomenon that ORNL demonstrated experimentally in the 1970s and 1980s. 

Three of the Belgian reactors' four questionable flaws were deemed compliant with safety regulations under pre-stress warming conditions. The remaining flaw, labeled flaw #1660, was cleared after closer scrutiny of its geometry. 

The initial screenings were performed with a simplification of the shape, in which each was assumed to be a circular disc—an approach that Bass calls “very conservative." When ORNL modeled flaw #1660 and found that it is an elliptical disc (roughly 8.5 millimeters across in one direction and 10 mm across in the other), it passed muster. 

"You change the problem and go back to the original representation that’s much closer to reality,” says Bass. "When we did that we found that the real flaw met the ASME code acceptance criteria.”  

ORNL did not estimate how big the RPVs' margin of safety is, but it is “significant” in Bass’ expert opinion: ”There is significant margin between the driving forces on the flaws and the toughness of the material."

ORNL also concurred with Electrabel’s calculations regarding the risk posed by hydrogen diffusing into the steel and forcing open cracks during temperature swings. "We looked at what they did and it looked reasonable to us,” says Bass.

FANC, meanwhile, concurred with Electrabel’s assertion, based on ultrasonic inspections in 2012 and 2014, that the flaws were created when the RPVs were forged and are not growing over time. Still, it approved the reactors to restart on the condition that Electrabel must reinspect the RPVs when they are next shut down for refuelling.

Several independent experts argued in 2014 that FANC had overlooked the risks posed by ongoing hydrogen diffusion. Among them was Digby Macdonald, a corrosion expert at the University of California at Berkeley. (Spectrum highlighted Macdonald’s concerns in April of this year.) 

FANC addressed their concerns in a special report released this week. The report cites input from several independent experts, including two proposed by Macdonald’s colleague Walter Bogaerts, a Belgian materials science expert. 

The independent experts affirmed that “significant experiment and theoretical results” constrain the pressure caused by hydrogen within the RPV to low levels: about 200 kilopascals at 25 degrees Celsius and 35 kPa at 300 °C. To put that in context, computations by Electrabel suggest that even hydrogen exerting 10 megapascals of pressure within the flaws would have a “small impact” on RPV integrity. 

Macdonald told IEEE Spectrum that he remains concerned about the FANC experts’ failure to “correctly address” the potential production of hydrogen within the reactor via radiolysis—the splitting of water molecules by nuclear radiation. However, he says he has yet to publish his own analysis of radiolysis.


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