University of Twente researchers have made significant efficiency improvements to the technology used to generate solar fuels. This involves the direct conversion of energy from sunlight into a usable fuel (in this case, hydrogen). Using only earth-abundant materials, they developed the most efficient conversion method to date. The trick was to decouple the site where sunlight is captured from the site where the conversion reaction takes place.

The study has been published in the journal Nature Energy.

Researchers around the world are working on the development of solar fuel technology. The research involves generating sustainable fuels using only sunlight, CO2 and water, the basic ingredients used by plants.

A group of researchers from the University of Twente’s MESA+ research institute are working on a solar-to-fuel device that produces hydrogen. They have now achieved a major breakthrough in this area of fundamental research. Using earth-abundant materials (i.e. avoiding the use of scarce and expensive precious metals), they have developed the most efficient method to date for converting light into hydrogen.

Microwires for solar fuel production. Image Credit: University of Twente. Click image for the largest view.

The system consists of silicon microwires less than one tenth of a millimeter long, the tops of which are coated with a catalyst. The photons (light particles) are collected between the microwires. The chemical reaction in which hydrogen is formed takes place on the catalyst at the tips of the microwires.

By varying the density and length of the microwires, the researchers ultimately achieved a maximum efficiency of 10.8 percent. They managed to achieve this by decoupling the site where the photons are collected from the site where the conversion reaction takes place. This is necessary because catalysts usually reflect light.

But, to make the conversion as efficient as possible you want them to absorb as much light as possible. It is important to achieve this decoupling at the microscale, because at larger scales the conductivity of the silicon microwires becomes the limiting factor.

Professor Jurriaan Huskens, one of the researchers involved, stated that 10.8 percent is the highest ever efficiency for a silicon-based design. However, a further increase in efficiency – to fifteen percent – is needed to make the technology economically viable.

Sounds great from a really brief press release. One suspects there is a rush to publish and a desire to get some patent work underway. 10.8 percent is a top of the line accomplishment suggesting the 15 percent line might be on its way. Lets hope they don’t stop there and the build costs are sensible.

Brookhaven National Laboratory scientists have observed an unexpected phenomenon in lithium-ion batteries – the most common type of battery used to power cell phones and electric cars. As a model battery generated electric current, the scientists witnessed the concentration of lithium inside individual nanoparticles reverse at a certain point, instead of constantly increasing.

This discovery, published in the journal Science Advances, is a major step toward improving the battery life of consumer electronics.

Esther Takeuchi, a SUNY distinguished professor at Stony Brook University and a chief scientist in the Energy Sciences Directorate at Brookhaven Lab said, “If you have a cell phone, you likely need to charge its battery every day, due to the limited capacity of the battery’s electrodes. The findings in this study could help develop batteries that charge faster and last longer.”

Inside every lithium-ion battery are particles whose atoms are arranged in a lattice – a periodic structure with gaps between the atoms. When a lithium-ion battery supplies electricity, lithium ions flow into empty sites in the atomic lattice.

This diagram shows the spread of positively charged lithium ions across the custom-built FeF2 nanoparticle. The conversion reaction sweeps rapidly across the surface before proceeding more slowly in a layer-by-layer fashion through the bulk of the particle. Image Credit: Brookhaven National Lab. Click image for the largest view.

Wei Zhang, a scientist at Brookhaven’s Sustainable Energy Technologies Department explained, “Previously, scientists assumed that the concentration of lithium would continuously increase in the lattice. But now, we have seen that this may not be true when the battery’s electrodes are made from nano-sized particles. We observed the lithium concentration within local regions of nanoparticles go up, and then down – it reversed.”

Electrodes are often made from nanoparticles in order to increase a battery’s power density. But scientists have not been able to fully understand how these electrodes function, due to a limited ability to watch them work in action. Now, with a unique combination of experimental tools, the scientists were able to image reactions inside the electrodes in real time.

Feng Wang, the leader of this study and a scientist in Brookhaven’s Sustainable Energy Technologies Department took the explanation further, “Similar to how a sponge soaks up water, we can see the overall level of lithium continuously increase inside the nano-sized particles. But unlike water, lithium may preferentially move out of some areas, creating inconsistent levels of lithium across the lattice.”

The scientists explained that uneven movement of lithium could have lasting, damaging effects because it strains the structure of the active materials in batteries and can lead to fatigue failure.

“Before lithium enters the lattice, its structure is very uniform,” Wang said. “But once lithium goes in, it stretches the lattice, and when lithium goes out, the lattice shrinks. So each time you charge and drain a battery, its active component will be stressed, and its quality will degrade over time. Therefore, it is important to characterize and understand how lithium concentration changes both in space and time.”

In order to make these observations, the scientists combined transmission electron microscopy (TEM) experiments, conducted at the Center for Functional Nanomaterials (CFN), a DOE Office of Science User Facility at Brookhaven Lab, and at Brookhaven’s Condensed Matter Physics and Materials Science Department, with x-ray analyses at the National Synchrotron Light Source (NSLS). NSLS is a DOE Office of Science user facility at Brookhaven that closed in 2014 when its successor, NSLS-II, opened.

Yimei Zhu, co-author of the study and a senior physicist at Brookhaven Lab said, “Wang’s team combined TEM with x-ray techniques. Both methods use a similar approach to analyze the structure of materials, but can provide complementary information. Electrons are sensitive to the local structure, while x-rays can probe a larger volume and enable much better statistics.”

The Brookhaven team also developed a nanoscale model battery that could mimic the function of lithium-ion batteries that would “fit” into a TEM. Computer simulations conducted at the University of Michigan further confirmed the surprising conclusions.

Katsuyo Thornton, a professor of materials science and engineering at the University of Michigan, Ann Arbor, who led the theoretical effort said, “We initially thought that the reversal mechanism was similar to those previously proposed, which stemmed from the interactions between nearby particles. However, it turned out a concentration reversal within a single particle could not be explained by existing theories, but rather, it arises from a different mechanism. Simulations were critical in this work because, without them, we would have made an incorrect conclusion.”

While the study focused on lithium-ion batteries, the scientists say the observed phenomenon may also occur in other high-performance battery chemistries.

Wang said, “Down the road, we plan to use the world-class facilities at CFN and NSLS-II to more closely examine how battery materials work, and to find solutions for building new batteries that can charge faster and last longer. These facilities offer the ideal tools for imaging the structure of battery materials in real time and under real-world conditions.”

It sure looks like some taxpayer money is paying off here. Portability of devices is just getting going and miniaturization is going to bring more tools and conveniences to us. Better batteries will get them here sooner and more powerful even faster.

Swiss EMPA researchers have succeeded in doubling the electrochemical stability of water with a special saline solution bringing us one step closer to using the technology commercially. This research could very well lead to a basis for a future with particularly inexpensive rechargeable batteries.

The press release begins by asking during the hunt to find safe, low-cost batteries for the future, eventually we have to ask ourselves a question: Why not simply use water as an electrolyte? Water is inexpensive, available everywhere, non-flammable and can conduct ions. However, water has one major drawback: It is chemically stable only up to a voltage of 1.23 volts. In other words, a water cell supplies three times less voltage than a customary lithium ion cell with 3.7 volts, which makes it poorly suited for applications in an electric car. A cost-effective, water-based battery, however, could be extremely interesting for stationary electricity storage applications.

Ruben-Simon Kühnel and David Reber, researchers in Empa’s Materials for Energy Conversion department, have now discovered a way to solve the problem: The salt containing electrolyte has to be liquid, but at the same time it has to be so highly concentrated that it does not contain any “excess” water.

Sodium bis(fluorosulfonyl)imide based aqueous electrolytes exhibit a wide electrochemical stability window of up to 2.6 V when the water-to-salt molar ratio falls below 2:1, enabling the fabrication of high-voltage rechargeable aqueous sodium-ion batteries. Image Credit EMPA. Click image for the largest view.

For their experiments, the two researchers used the special salt sodium FSI (precise name: sodium bis(fluorosulfonyl)imide). This salt is extremely soluble in water: seven grams of sodium FSI and one gram of water produce a clear saline solution (see video clip). In this liquid, all water molecules are grouped around the positively charged sodium cations in a hydrate shell, virtually no unbound water molecules remain. Thus making an aqueous sodium ion battery.

The research paper has been published in the American Chemical Society’s Energy Letters.

The researchers discovered that this saline solution displays an electrochemical stability of up to 2.6 volts – i.e. nearly twice as much as other aqueous electrolytes. The discovery could be the key to inexpensive, safe battery cells; inexpensive because, apart from anything else, the sodium FSI cells can be constructed more safely and thus more easily than the familiar lithium ion batteries.

The system has already withstood a series of charging and discharging cycles in the lab. Until now, however, the researchers have been testing the anodes and cathodes of their test battery separately – against a standard electrode as a partner. In the next step, the two half cells are to be combined into a single battery. Then additional charging and discharging cycles are scheduled.

Empa’s research activities on novel batteries for stationary electricity storage systems are embedded in the Swiss Competence Center for Heat and Electricity Storage (SCCER HaE), which coordinates research for new heat and electricity storage concepts on a national level and is led by the Paul Scherrer Institute (PSI). If the experiment succeeds, inexpensive water batteries will be within reaching distance.

This research may have immense implications for the intermittent energy producers. Storing the energy in the face of way too expensive production strongly needs full productive output and metered release to gain more credible traction in the market. For now these alternatives can only operate with government forcing, a prospect that can not last much longer with competitive pressure mounting.

National University of Singapore researchers have pioneered a new water-based air-conditioning system that cools air to as low as 18º C (64.4º F) without using energy-intensive compressors and environmentally harmful chemical refrigerants.

This disruptive type of technology could potentially replace the century-old air-cooling principle that is still being used in our modern-day air-conditioners. Suitable for both indoor and outdoor use, the novel system is portable and it can also be customized for all types of weather conditions.

NUS Engineering researchers developed a novel air cooling technology that could redefine the future of air-conditioning. Image Credit: National University of Singapore. Click image for the largest view.

Led by Associate Professor Ernest Chua from the Department of Mechanical Engineering at NUS Faculty of Engineering, the team’s novel air-conditioning system is cost-effective to produce, and it is also more eco-friendly and sustainable. The system consumes about 40 percent less electricity than current compressor-based air-conditioners used in homes and commercial buildings. This translates into more than a 40 percent reduction in carbon emissions. In addition, it adopts a water-based cooling technology instead of using chemical refrigerants such as chlorofluorocarbon and hydrochlorofluorocarbon for cooling, thus making it safer and more environmentally-friendly.

Adding another feather to its eco-friendliness cap, the novel system generates potable drinking water while it cools the ambient air.

Associate Prof Chua said, “For buildings located in the tropics, more than 40 percent of the building’s energy consumption is attributed to air-conditioning. We expect this rate to increase dramatically, adding an extra punch to global warming. First invented by Willis Carrier in 1902, vapor compression air-conditioning is the most widely used air-conditioning technology today. This approach is very energy-intensive and environmentally harmful. In contrast, our novel membrane and water-based cooling technology is very eco-friendly – it can provide cool and dry air without using a compressor and chemical refrigerants. This is a new starting point for the next generation of air-conditioners, and our technology has immense potential to disrupt how air-conditioning has traditionally been provided.”

Current air-conditioning systems require a large amount of energy to remove moisture and to cool the dehumidified air. By developing two systems to perform these two processes separately, the NUS Engineering team can better control each process and hence achieve greater energy efficiency.

The novel air-conditioning system first uses an innovative membrane technology – a paper-like material – to remove moisture from humid outdoor air. The dehumidified air is then cooled via a dew-point cooling system that uses water as the cooling medium instead of harmful chemical refrigerants. Unlike vapor compression air-conditioners, the novel system does not release hot air to the environment. Instead, a cool air stream that is comparatively less humid than environmental humidity is discharged – negating the effect of micro-climate. About 12 to 15 liters of potable drinking water can also be harvested after operating the air-conditioning system for a day.

Associate Prof Chua explained, “Our cooling technology can be easily tailored for all types of weather conditions, from humid climate in the tropics to arid climate in the deserts. While it can be used for indoor living and commercial spaces, it can also be easily scaled up to provide air-conditioning for clusters of buildings in an energy-efficient manner. This novel technology is also highly suitable for confined spaces such as bomb shelters or bunkers, where removing moisture from the air is critical for human comfort, as well as for sustainable operation of delicate equipment in areas such as field hospitals, armored personnel carriers, and operation decks of navy ships as well as aircraft.”

The research team is currently refining the design of the air-conditioning system to further improve its user-friendliness. The NUS researchers are also working to incorporate smart features such as pre-programmed thermal settings based on human occupancy and real-time tracking of its energy efficiency. The team hopes to work with industry partners to commercialize the technology.

Looks and sounds good. But that discharge temperature looks barely adequate for the developed world’s jaded consumers. Drying the air will make huge difference, cooling the circulating air far enough to condense out the water vapor is a big part of the A/C energy cost. So it looks like a sure half way, first step, kind of thing.

The approach is also a sophisticated look at A/C as its done now. Going to two steps with such impressive results is sure to cause an engineering rethink for current designs marketed in the developed world now. Is it a revolution or disruptive technology? Almost.

Where new installations with capital cost decisions are tight and running expense is a concern, this technology should find a warm reception.

Rice University scientists show in simulations how carbon nanomaterials may be optimized to replace the expensive platinum in cathodes for electricity-generating fuel cells. The plan is for nitrogen doped carbon nanotubes or modified graphene nanoribbons to be suitable replacements for platinum for fast oxygen reduction, the key reaction in fuel cells that transform chemical energy into electricity.

Simulations by Rice University scientists show how carbon nanomaterials may be optimized to replace expensive platinum in cathodes for electricity-generating fuel cells. Image Credit: Yakobson Research Group. Click image for the largest view.

The findings are from computer simulations by Rice scientists who set out to see how carbon nanomaterials can be improved for fuel-cell cathodes. Their study reveals the atom-level mechanisms by which doped nanomaterials catalyze oxygen reduction reactions (ORR).

The research paper has been published in the Royal Society of Chemistry journal Nanoscale.

Theoretical physicist Boris Yakobson and his Rice colleagues are among many looking for a way to speed up ORR for fuel cells, which were discovered in the 19th century but not widely used until the latter part of the 20th. They have since powered transportation modes ranging from cars and buses to spacecraft.

The Rice researchers, including lead author and former postdoctoral associate Xiaolong Zou and graduate student Luqing Wang, used computer simulations to discover why graphene nanoribbons and carbon nanotubes modified with nitrogen and/or boron, long studied as a substitute for expensive platinum, are so sluggish and how they can be improved.

Doping, or chemically modifying, conductive nanotubes or nanoribbons changes their chemical bonding characteristics. They can then be used as cathodes in proton-exchange membrane fuel cells. In a simple fuel cell, anodes draw in hydrogen fuel and separate it into protons and electrons. While the negative electrons flow out as usable current, the positive protons are drawn to the cathode, where they recombine with returning electrons and oxygen to produce water.

The models showed that thinner carbon nanotubes with a relatively high concentration of nitrogen would perform best, as oxygen atoms readily bond to the carbon atom nearest the nitrogen. Nanotubes have an advantage over nanoribbons because of their curvature, which distorts chemical bonds around their circumference and leads to easier binding, the researchers found.

The tricky bit is making a catalyst that is neither too strong nor too weak as it bonds with oxygen. The curve of the nanotube provides a way to tune the nanotubes’ binding energy, according to the researchers, who determined that “ultrathin” nanotubes with a radius between 7 and 10 angstroms would be ideal. (An angstrom is one ten-billionth of a meter; for comparison, a typical atom is about 1 angstrom in diameter.)

They also showed co-doping graphene nanoribbons with nitrogen and boron enhances the oxygen-absorbing abilities of ribbons with zigzag edges. In this case, oxygen finds a double-bonding opportunity. First, they attach directly to positively charged boron-doped sites. Second, they’re drawn by carbon atoms with high spin charge, which interacts with the oxygen atoms’ spin-polarized electron orbitals. While the spin effect enhances adsorption, the binding energy remains weak, also achieving a balance that allows for good catalytic performance.

The researchers showed the same catalytic principles held true, but to lesser effect, for nanoribbons with armchair edges.

“While doped nanotubes show good promise, the best performance can probably be achieved at the nanoribbon zigzag edges where nitrogen substitution can expose the so-called pyridinic nitrogen, which has known catalytic activity,” Yakobson said.

“If arranged in a foam-like configuration, such material can approach the efficiency of platinum,” Wang said. “If price is a consideration, it would certainly be competitive.”

Zou is now an assistant professor at Tsinghua-Berkeley Shenzhen Institute in Shenzhen City, China. Yakobson is the Karl F. Hasselmann Professor of Materials Science and NanoEngineering and a professor of chemistry.

Other than perhaps spacecraft, price is definitely a consideration. So, there is more to be done. We’ve seen several platinum replacement ideas over the years but there isn’t one blasting off commercially. There are lost of working ideas on coming up with hydrogen fuels and carriers for the fuel. We still need storage and economical fuel cells. Lets hope this team isn’t done with the research – no platinum is a big incentive.


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