MIT researchers have found a way to substantially reduce metal air battery corrosion, making it possible for such batteries to have much longer shelf lives. Metal-air batteries are one of the lightest and most compact types of batteries available, but they can have a major limitation: When not in use, they degrade quickly, as corrosion eats away at their metal electrodes.

While typical rechargeable lithium-ion batteries only lose about 5 percent of their charge after a month of storage, they are too costly, bulky, or heavy for many applications. Primary (nonrechargeable) aluminum-air batteries are much less expensive and more compact and lightweight, but they can lose 80 percent of their charge a month.

The MIT design overcomes the problem of corrosion in aluminum-air batteries by introducing an oil barrier between the aluminum electrode and the electrolyte – the fluid between the two battery electrodes that eats away at the aluminum when the battery is on standby. The oil is rapidly pumped away and replaced with electrolyte as soon as the battery is used. As a result, the energy loss is cut to just 0.02 percent a month – more than a thousandfold improvement.

Metal Air Battery Corrosion Protection Demonstrated. Image Credit: Researchers at MIT. Click image for the largest view.

The findings have been published in the journal Science by former MIT graduate student Brandon J. Hopkins ’18, W.M. Keck Professor of Energy Yang Shao-Horn, and professor of mechanical engineering Douglas P. Hart.

While several other methods have been used to extend the shelf life of metal-air batteries (which can use other metals such as sodium, lithium, magnesium, zinc, or iron), these methods can sacrifice performance Hopkins said. Most of the other approaches involve replacing the electrolyte with a different, less corrosive chemical formulation, but these alternatives drastically reduce the battery power.

Other methods involve pumping the liquid electrolyte out during storage and back in before use. These methods still enable significant corrosion and can clog plumbing systems in the battery pack. Because aluminum is hydrophilic (water-attracting) even after electrolyte is drained out of the pack, the remaining electrolyte will cling to the aluminum electrode surfaces. “The batteries have complex structures, so there are many corners for electrolyte to get caught in,” which results in continued corrosion, Hopkins explained.

A key to the new system is a thin membrane placed between the battery electrodes. When the battery is in use, both sides of the membrane are filled with a liquid electrolyte, but when the battery is put on standby, oil is pumped into the side closest to the aluminum electrode, which protects the aluminum surface from the electrolyte on the other side of the membrane.

The new battery system also takes advantage of a property of aluminum called “underwater oleophobicity” – that is, when aluminum is immersed in water, it repels oil from its surface. As a result, when the battery is reactivated and electrolyte is pumped back in, the electrolyte easily displaces the oil from the aluminum surface, which restores the power capabilities of the battery. Ironically, the MIT method of corrosion suppression exploits the same property of aluminum that promotes corrosion in conventional systems.

The result is an aluminum-air prototype with a much longer shelf life than that of conventional aluminum-air batteries. The researchers showed that when the battery was repeatedly used and then put on standby for one to two days, the MIT design lasted 24 days, while the conventional design lasted for only three. Even when oil and a pumping system are included in scaled-up primary aluminum-air battery packs, they are still five times lighter and twice as compact as rechargeable lithium-ion battery packs for electric vehicles, the researchers report.

Hart explained that aluminum, besides being very inexpensive, is one of the “highest chemical energy-density storage materials we know of” – that is, it is able to store and deliver more energy per pound than almost anything else, with only bromines, which are expensive and hazardous, being comparable. He says many experts think aluminum-air batteries may be the only viable replacement for lithium-ion batteries and for gasoline in cars.

Aluminum-air batteries have been used as range extenders for electric vehicles to supplement built-in rechargeable batteries, to add many extra miles of driving when the built-in battery runs out. They are also sometimes used as power sources in remote locations or for some underwater vehicles. But while such batteries can be stored for long periods as long as they are unused, as soon as they are turned on for the first time, they start to degrade rapidly.

Such applications could greatly benefit from this new system, Hart explains, because with the existing versions, “you can’t really shut it off. You can flush it and delay the process, but you can’t really shut it off.” However, if the new system were used, for example, as a range extender in a car, “you could use it and then pull into your driveway and park it for a month, and then come back and still expect it to have a usable battery. . . I really think this is a game-changer in terms of the use of these batteries.”

With the greater shelf life that could be afforded by this new system, the use of aluminum-air batteries could “extend beyond current niche applications,” says Hopkins. The team has already filed for patents on the process.

This might be super news if the process technology gets to scale. There is also another metal air market that is being overlooked, the hearing aids. That markets doesn’t seem large and the batteries are tiny, but there are millions of them being sold. And the battery issue drives lots of users – nuts.

Harvard researchers have developed an improved system to use renewable electricity to reduce carbon dioxide into carbon monoxide to recycle carbon dioxide.

Imagine a day when – rather than being spewed into the atmosphere – the gases coming from power plants and heavy industry are instead captured and fed into catalytic reactors that chemically transform greenhouse gases like carbon dioxide into industrial fuels or chemicals and that emit only oxygen.

CO2 to CO Process Graph Rowland at Harvard. Image Credit: Haotian Wang, the Rowland Institute, Harvard University. Click image for the largest view.

It’s a future that Haotian Wang, a fellow at the Rowland Institute at Harvard, says may be closer than many realize.

Wang and his colleagues have developed an improved system to use renewable electricity to reduce carbon dioxide into carbon monoxide – a key commodity used in a number of industrial processes. The system is described in a paper published in Joule, a newly launched sister journal of Cell press.

Wang said, “The most promising idea may be to connect these devices with coal-fired power plants or other industry that produces a lot of CO2. About 20 percent of those gases are CO2, so if you can pump them into this cell. . . and combine it with clean electricity, then we can potentially produce useful chemicals out of these wastes in a sustainable way, and even close part of that CO2 cycle.”

The new system, Wang said, represents a dramatic step forward from the one he and colleagues first described in a 2017 paper in Chem.

Where that old system was barely the size of a cell phone and relied on two electrolyte-filled chambers, each of which held an electrode, the new system is cheaper and relies on high concentrations of CO2 gas and water vapor to operate more efficiently – just one 10-by-10-centimeter cell, Wang said, can produce as much as four liters of CO per hour.

The new system, Wang said, addresses the two main challenges – cost and scalability – that were seen as limiting the initial approach.

“In that earlier work, we had discovered the single nickel-atom catalysts which are very selective for reducing CO2 to CO. . . but one of the challenges we faced was that the materials were expensive to synthesize,” Wang said. “The support we were using to anchor single nickel atoms was based on graphene, which made it very difficult to scale up if you wanted to produce it at gram or even kilogram scale for practical use in the future.”

To address that problem, he said, his team turned to a commercial product that’s thousands of times cheaper than graphene as an alternative support – carbon black.

Using a process similar to electrostatic attraction, Wang and colleagues are able to absorb single nickel atoms (positively charged) into defects (negatively charged) in carbon black nanoparticles, with the resulting material being both low-cost and highly selective for CO2 reduction.

“Right now, the best we can produce is grams, but previously we could only produce milligrams per batch,” Wang said. “But this is only limited by the synthesis equipment we have; if you had a larger tank, you could make kilograms or even tons of this catalyst.”

The other challenge Wang and colleagues had to overcome was tied to the fact that the original system only worked in a liquid solution.

The initial system worked by using an electrode in one chamber to split water molecules into oxygen and protons. As the oxygen bubbled away, protons conducted through the liquid solution would move into the second chamber, where – with the help of the nickel catalyst – they would bind with CO2 and break the molecule apart, leaving CO and water. That water could then be fed back into the first chamber, where it would again be split, and the process would start again.

“The problem was that, the CO2 we can reduce in that system are only those dissolved in water; most of the molecules surrounding the catalyst were water,” he said. “There was only a trace amount of CO2, so it was pretty inefficient.”

While it may be tempting to simply increase the voltage applied on the catalyst to increase the reaction rate, that can have the unintended consequence of splitting water, not reducing CO2, Wang said.

“If you deplete the CO2 that’s close to the electrode, other molecules have to diffuse to the electrode, and that takes time,” Wang said. “But if you’re increasing the voltage, it’s more likely that the surrounding water will take that opportunity to react and split into hydrogen and oxygen.”

The solution proved to be relatively simple – to avoid splitting water, the team took the catalyst out of solution.

“We replaced that liquid water with water vapor, and feed in high-concentration CO2 gas,” he said. “So if the old system was more than 99 percent water and less than 1 percent CO2, now we can completely reverse that, and pump 97 percent CO2 gas and only 3 percent water vapor into this system. Before that liquid water also functions as ion conductors in the system, and now we use ion exchange membranes instead to help ions move around without liquid water.”

“The impact is that we can deliver an order of magnitude higher current density,” he continued. “Previously, we were operating at about ten milliamps-per-centimeter squared, but today we can easily ramp up to 100 milliamps.”

Going forward, Wang said, the system still has challenges to overcome – particularly related to stability.

“If you want to use this to make an economic or environmental impact, it needs to have a continuous operations of thousands of hours,” he said. “Right now, we can do this for tens of hours, so there’s still a big gap, but I believe those problems can be addressed with more detailed analysis of both the CO2 reduction catalyst and the water oxidation catalyst.”

Ultimately, Wang said, the day may come when industry will be able to capture the CO2 that is now released into the atmosphere and transform it into useful products.

“Carbon monoxide is not a particularly high value chemical product,” Wang said. “To explore more possibilities, my group has also developed several copper-based catalysts that can further reduce CO2 into products that are much more valuable.”

Wang credited the freedom he enjoyed at the Rowland Institute for helping lead to breakthroughs like the new system.

“Rowland has provided me, as an early career researcher, a great platform for independent research, which initiates a large portion of the research directions my group will continue to push forward,” said Wang, who recently accepted a position at Rice University. “I will definitely miss my days here.”

Good news followed by a career move that may close this research. Lets hope not. The energy economy needs to get further along in being part of the planet’s carbon cycle.

Dr. Michael Van Zeeland from General Atomics, led the research by international team that was composed of more than 30 scientists from across the globe who worked together to develop an approach to keep the fusion plasma in check.

To harness fusion energy fast plasma particles can be confined by a strong magnetic field, which guides the particles along a closed path. If the particles get knocked off their closed path, they make fusion less efficient and can even damage the fusion device. Scientists, therefore, are looking for ways to prevent the energetic particles from veering off course.

One way a particle can be kicked out of the fusion device is by interacting with waves. Just as a boat in a lake can be jostled by waves passing by, a particle in a plasma can get a boost of energy from waves moving along the magnetic field used to confine the plasma.

In the work here, the waves are called Alfvén waves named after the Nobel Prize winner Hannes Alfvén who discovered them. Such waves are problematic for future tokamak fusion reactors because they make it more challenging to keep the plasma hot and undergoing fusion.

Dr. Van Zeeland said, “Controlling these waves helps us hold onto the fast particles that heat fusion plasmas.”

The research, which was conducted at the DIII-D National Fusion Facility in San Diego, California, and the ASDEX-Upgrade facility in Germany, was presented at the American Physical Society Division of Plasma Physics meeting in Portland, Oregon. The scientists used a specific kind of microwaves, electron cyclotron waves, which they precisely directed near the location of the waves on the magnetic field. The microwaves were found to modify the wave activity significantly – in some cases completely removing them.

This research yielded insight into these particular microwaves and how they interact with waves on the magnetic fields. The researchers believe the results can lead to the development of approaches to control or reduce the presence of waves on the magnetic fields and could help chart a path to more efficient fusion energy.

The tokamak idea stays alive with another technology that may well have significant use in other fields. Oddly, the tokamak fusion concept is getting new technological results in close by and supporting fields. It looks more and more like the scenario that occurred in the sixties during the race to the moon. Maybe not an economic disrupter, more like a minor contributor so far.

Imagine building a machine so advanced and precise you need a supercomputer to help design it. That’s exactly what scientists and engineers in Germany did when building the Wendelstein 7-X experiment. The device, funded by the German federal and state governments and the European Union, is a type of fusion device called a stellarator. The new experiment’s goal is to contain a super-heated gas, called plasma, in a donut-shaped vessel using magnets that twist their way around the donut.

The team completed construction of Wendelstein 7-X, the world’s most advanced superconducting stellarator, in 2015 and, since then, scientists have been busy studying its performance.

Wendelstein 7-X Experiment Hall. Image Credit: Max Planck Institute For Plasma Physics. Click image for the largest view.

Dr. Novimir Pablant, a U.S. physicist from the Princeton Plasma Physics Laboratory, who works alongside a multinational team of scientists and engineers from Europe, Australia, Japan, and the United States (the U.S. collaboration is funded by the Department of Energy) said, “The advantage of stellarators over other types of fusion machines is that the plasmas produced are extremely stable and very high densities are possible.”

Using a tool called an X-ray spectrometer, Pablant studied the light given off by the plasma to answer an important question: Did the design of Wendelstein 7-X’s twisted magnetic field work? His results indicate that, indeed, the plasma temperatures and electric fields are already in the range required for peak performance. He will present his work at the American Physical Society Division of Plasma Physics conference in Portland, Oregon.

If the scientists working on Wendelstein 7-X are successful in optimizing the machine performance, the plasma contained in the donut will become even hotter than the sun. Atoms making up the plasma will fuse together, yielding safe, clean energy to be used for power. This achievement is a major milestone as it shows that it is possible to achieve temperatures of more than 10 million degrees in high-density plasmas using only microwaves to heat the electrons in the plasma. This achievement takes the research one step closer to making fusion power a reality.

Lets hope they get to net energy output soon. It seems like some group or another might get there next year. That might really ensure the economic success of the modern world. Energy is fundamental to modern economics and a low cost vast supply of electricity would assure the world continues to progress.

Ecole Polytechnique Fédérale de Lausanne (EPFL) researchers have developed a photocatalytic system based on a material in the class of metal-organic frameworks. The system can be used to degrade pollutants present in water while simultaneously producing hydrogen that can be captured and further used.

Simultaneous photocatalytic hydrogen generation and dye degradation using a visible light active metal–organic framework. Image Credit: Alina-Stavroula Kampouri/EPFL.  Click image for the largest view.

Some of the most useful and versatile materials today are the metal-organic frameworks (MOFs). MOFs are a class of materials demonstrating structural versatility, high porosity, fascinating optical and electronic properties, all of which makes them promising candidates for a variety of applications, including gas capture and separation, sensors, and photocatalysis.

Because MOFs are so versatile in both their structural design and usefulness, material scientists are currently testing them in a number of chemical applications. One of these is photocatalysis, a process where a light-sensitive material is excited with light. The absorbed excess energy dislocates electrons from their atomic orbits, leaving behind “electron holes”. The generation of such electron-hole pairs is a crucial process in any light-dependent energy process, and, in this case, it allows the MOF to affect a variety of chemical reactions.

A team of scientists at EPFL Sion led by Kyriakos Stylianou at the Laboratory of Molecular Simulation, have now developed a MOF-based system that can perform not one, but two types of photocatalysis simultaneously: production of hydrogen, and cleaning pollutants out of water. The material contains the abundantly available and cheap nickel phosphide (Ni2P), and was found to carry out efficient photocatalysis under visible light, which accounts to 44% of the solar spectrum.

The first type of photocatalysis, hydrogen production, involves a reaction called “water-splitting”. Like the name suggests, the reaction divides water molecules into their constituents: hydrogen and oxygen. One of the bigger applications here is to use the hydrogen for fuel cells, which are energy-supply devices used in a variety of technologies today, including satellites and space shuttles.

The second type of photocatalysis is referred to as “organic pollutant degradation,” which refers to processes breaking down pollutants present in water. The scientists investigated this innovative MOF-based photocatalytic system towards the degradation of the toxic dye rhodamine B, commonly used to simulate organic pollutants.

The scientists performed both tests in sequence, showing that the MOF-based photocatalytic system was able to integrate the photocatalytic generation of hydrogen with the degradation of rhodamine B in a single process. This means that it is now possible to use this photocatalytic system to both clean pollutants out of water, while simultaneously producing hydrogen that can be used as a fuel.

Kyriakos Stylianou said, “This noble-metal free photocatalytic system brings the field of photocatalysis a step closer to practical ‘solar-driven’ applications and showcases the great potential of MOFs in this field.”

Stylianou’s group has had their paper published in Advanced Functional Materials.

Its reasonable to expect this material or its derivatives will come to market. Perhaps not a direct hydrogen producer, but in combination with clean up efforts. Fuel cells are coming along pretty well, and this product also isn’t using noble metals, another huge plus. Now if someone can find the hydrogen storage materials . . .


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