Pusan National University researchers have invented a new sodium ion anode material. They are using a recently developed pyrolyzed quinacridones, new carbonaceous anode materials, that are efficient, easily prepared, and exhibit excellent electrochemical properties, including high sodium-ion storage performance and cycling stability.

Their study paper was made available online on October of 2022 and will be published in Volume 453, Part 1 of the Chemical Engineering Journal on 1 February 2023.

Pyrolyzed quinacridones-based carbonaceous sodium-ion battery anode infographic. Image Credit: Pusan National University. Click the press release link for a larger image.

Lithium-ion batteries have high energy density and a long cycle life, making them indispensable in portable electronics as well as electric vehicles. However, the high cost and limited supply of lithium necessitate the development of alternative energy storage systems. To this end, researchers have suggested sodium-ion batteries (SIBs) as a possible candidate.

However, sodium ions, being large and sluggish, hamper sodium-ion battery (SIB) anode performance.

Along with having physicochemical properties similar to that of lithium, sodium is both sustainable and cost-effective. However, its ions are large with sluggish diffusion kinetics, hindering their accommodation within the carbon microstructures of the commercialized graphite anodes. Consequently, SIB anodes suffer from structural instability and poor storage performance. In this regard, carbonaceous materials doped with heteroatoms are showing promise. However, their preparation is complicated, expensive, and time-consuming.

Recently, a team of researchers, led by Professor Seung Geol Lee from Pusan National University in Korea, used quinacridones as precursors to prepare carbonaceous SIB anodes.

Prof. Lee explained, “Organic pigments such as quinacridones have a variety of structures and functional groups. As a result, they develop different thermal decomposition behaviors and microstructures. When used as a precursor for energy storage materials, pyrolyzed quinacridones can greatly vary the performance of secondary batteries. Therefore, it is possible to implement a highly efficient battery by controlling the structure of organic pigments precursor.”

The researchers focused on 2,9-dimethylquinacridone (2,9-DMQA) in their study. 2,9-DMQA has a parallel molecular packing configuration. Upon pyrolysis (thermal decomposition) at 600° C, 2,9-DMQA turned from reddish to black with a high char yield of 61%. The researchers next performed a comprehensive experimental analysis to describe the underlying pyrolysis mechanism.

They proposed that the decomposition of methyl substituents generates free radicals at 450° C, which form polycyclic aromatic hydrocarbons with a longitudinally grown microstructure resulting from bond bridging along the parallel packing direction. Further, nitrogen- and oxygen-containing functional groups in 2,9-DMQA released gases, creating disordered domains in the microstructure. In contrast, pyrolyzed unsubstituted quinacridone developed highly aggregated structures. This suggested that the morphological development was significantly affected by the crystal orientation of the precursor.

In addition, 2,9-DMQA pyrolyzed at 600° C exhibited a high rate capability (290 mAh/g at 0.05 A/g ) and excellent cycle stability (134 mAh/g at 5 A/g for 1000 cycles) as an SIB anode. The nitrogen- and oxygen-containing groups further enhanced battery storage via surface confinement and interlayer distance increment.

Prof. Lee summed up with, “Organic pigments such as quinacridones can be used as anode materials in sodium-ion batteries. Given the high efficiency, they will provide an effective strategy for mass production of large-scale energy storage systems.”

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This could very well be a sodium battery milestone. A 1000 cycle test is impressive. What’s not been said is the capacity and weight projections, the operating voltage and temperature range. These things matter and one hopes that the study paper shows more info.

The press release is pretty technical and misses lots of the info the casual observer would like to know. For now, the sodium battery anode problem looks to have its first solution at hand. More to come across the entire sodium research field – that’s a sure thing.

Ecole Polytechnique Fédérale de Lausanne chemical engineers have invented a solar-powered artificial leaf, built on a novel electrode which is transparent and porous. The artificial leaf is capable of harvesting water from the atmosphere for conversion into hydrogen fuel. The semiconductor-based technology is scalable and easy to prepare.

The paper reporting the results has been published in Advanced Materials.

A device that can harvest water from the air and provide hydrogen fuel – entirely powered by solar energy – has been a dream for researchers for decades. Now, EPFL chemical engineer Kevin Sivula and his team have made a significant step towards bringing this vision closer to reality.

The team has developed an ingenious yet simple system that combines semiconductor-based technology with novel electrodes that have two key characteristics: they are porous, to maximize contact with water in the air; and transparent, to maximize sunlight exposure of the semiconductor coating. When the device is simply exposed to sunlight, it takes water from the air and produces hydrogen gas.

The prime invention is their novel gas diffusion electrodes, which are transparent, porous and conductive, enabling this solar-powered technology for turning water – in its gas state from the air – into hydrogen fuel.

Sivula of EPFL’s Laboratory for Molecular Engineering of Optoelectronic Nanomaterials and principal investigator of the study said, “To realize a sustainable society, we need ways to store renewable energy as chemicals that can be used as fuels and feedstocks in industry. Solar energy is the most abundant form of renewable energy, and we are striving to develop economically-competitive ways to produce solar fuels.”

Inspiration from a plant’s leaf

In their research for renewable fossil-free fuels, the EPFL engineers in collaboration with Toyota Motor Europe, took inspiration from the way plants are able to convert sunlight into chemical energy using carbon dioxide from the air. A plant essentially harvests carbon dioxide and water from its environment, and with the extra boost of energy from sunlight, can transform these molecules into sugars and starches, a process known as photosynthesis. The sunlight’s energy is stored in the form of chemical bonds inside of the sugars and starches.

The transparent gas diffusion electrodes developed by Sivula and his team, when coated with a light harvesting semiconductor material, indeed act like an artificial leaf, harvesting water from the air and sunlight to produce hydrogen gas. The sunlight’s energy is stored in the form of hydrogen bonds.

Instead of building electrodes with traditional layers that are opaque to sunlight, their substrate is actually a 3-dimensional mesh of felted glass fibers.

Marina Caretti, lead author of the work, said, “Developing our prototype device was challenging since transparent gas-diffusion electrodes have not been previously demonstrated, and we had to develop new procedures for each step. However, since each step is relatively simple and scalable, I think that our approach will open new horizons for a wide range of applications starting from gas diffusion substrates for solar-driven hydrogen production.”

From liquid water to humidity in the air

Sivula and other research groups have previously shown that it is possible to perform artificial photosynthesis by generating hydrogen fuel from liquid water and sunlight using a device called a photoelectrochemical (PEC) cell. A PEC cell is generally known as a device that uses incident light to stimulate a photosensitive material, like a semiconductor, immersed in liquid solution to cause a chemical reaction. But for practical purposes, this process has its disadvantages e.g. it is complicated to make large-area PEC devices that use liquid.

Sivula wanted to show that the PEC technology can be adapted for harvesting humidity from the air instead, leading to the development of their new gas diffusion electrode. Electrochemical cells (e.g. fuel cells) have already been shown to work with gases instead of liquids, but the gas diffusion electrodes used previously are opaque and incompatible with the solar-powered PEC technology.

Now, the researchers are focusing their efforts into optimizing the system. What is the ideal fiber size? The ideal pore size? The ideal semiconductors and membrane materials? These are questions that are being pursued in the EU Project “Sun-to-X,” which is dedicated to advance this technology, and develop new ways to convert hydrogen into liquid fuels.

Making transparent, gas-diffusion electrodes

In order to make transparent gas diffusion electrodes, the researchers start with a type of glass wool, which is essentially quartz (also known as silicon oxide) fibers and process it into felt wafers by fusing the fibers together at high temperature. Next, the wafer is coated with a transparent thin film of fluorine-doped tin oxide, known for its excellent conductivity, robustness and ease to scale-up.

These first steps result in a transparent, porous, and conducting wafer, essential for maximizing contact with the water molecules in the air and letting photons through. The wafer is then coated again, this time with a thin-film of sunlight-absorbing semiconductor materials. This second thin coating still lets light through, but appears opaque due to the large surface area of the porous substrate. As is, this coated wafer can already produce hydrogen fuel once exposed to sunlight.

The scientists went on to build a small chamber containing the coated wafer, as well as a membrane for separating the produced hydrogen gas for measurement. When their chamber is exposed to sunlight under humid conditions, hydrogen gas is produced, achieving what the scientists set out to do, showing that the concept of a transparent gas- diffusion electrode for solar-powered hydrogen gas production can be achieved.

While the scientists did not formally study the solar-to-hydrogen conversion efficiency in their demonstration, they acknowledge that it is modest for this prototype, and currently less than can be achieved in liquid-based PEC cells. Based on the materials used, the maximum theoretical solar-to-hydrogen conversion efficiency of the coated wafer is 12%, whereas liquid cells have been demonstrated up to 19% efficient.

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This is a major milestone. No preprocessing (cleaning the water) adding acid salts, etc. Probably sets up anywhere the sun shines and the humidity is high enough. The only missing piece is combining oxygen into O2.

This breakthrough is just a few weeks old. It would not be a surprise that research will massively increase the efficiency. We’re going to be watching. In some respects this technology makes more practical sense than generating electricity.

The ARC Centre of Excellence in Exciton Science demonstrated a new pathway to creating durable, efficient perovskite photovoltaics at industrial scale. The process uses the first effective use of lead acetate as a precursor in making formamidinium-caesium perovskite solar cells.

The team at Exciton Science, based at Monash University, were able to create perovskite solar cells with 21% efficiency, the best results ever recorded for a device made from a non-halide lead source.

The reporting paper has been published in the journal Energy & Environmental Science.

A miniature prototype solar panel featuring these cells achieved 18.8% efficiency. The large-area perovskite layer was fabricated in ambient atmosphere and was made via a single-step blade coating, demonstrating its potential viability for industrial-scale manufacturing.

Ammonium is the secret ingredient in stable, efficient & scalable perovskite solar cells. Image Credit: © ARC Centre of Excellence in Exciton Science. Click the press release link for a larger image.

The test devices also showed strong thermal stability, continuing to function with no efficiency loss after 3,300 hours running at 65° C (149° F).

First author Jie Zhao, a PhD student at Monash University, said, “We’ve been able to use lead acetate in a one-step, spin-coating process to get the perfect, high-quality formamidinium-caesium perovskite thin film. And because we don’t need an anti-solvent agent, we can do this via large-scale techniques, such as blade coating, which means it’s viable at industrial scale.”

Corresponding author and Monash University colleague Dr Wenxin Mao said, “The vast majority of perovskite solar cell research uses lead halides, particularly lead iodide. The lead iodide needs to be 99.99% pure and it’s very expensive to synthesize cells using lead iodide.””We’re the first group to make highly stable formamidinium-cesium perovskite solar cells using lead acetate rather than lead iodide. We have provided the entire research community a second way to make high-quality perovskite solar cells,” he added.

More about perovskites: Promise versus problems

Thin film solar cells made from perovskites have the potential to disrupt the solar energy sector, thanks to their relatively low manufacturing cost, flexibility and tunable band gap relative to silicon.

However, researchers are struggling to solve reliability issues, and they also need to find a way to create devices at a viable commercial scale. Perovskites are solution processed (made in liquid) using a variety of different ingredients.

Most approaches use lead halides and require the inclusion of strong polar solvents with high boiling points and antisolvent quenching agents to control the perovskite crystallization process. This complicated mechanism can lead to defects in the thin films, which causes the resulting device to rapidly lose efficiency. It’s also hard to control.

The chemical compound lead acetate has emerged as a promising alternative precursor, because it can create ultrasmooth thin films with fewer defects. Until now, lead acetate had only been used to make methylammonium or cesium-based perovskites, which are relatively unstable and not suitable for real-world applications.

A better candidate for commercial use can be found in perovskites made using formamidinium and caesium, thanks to their superior stability. Previous attempts to synthesize them using lead acetate as the precursor failed.

To investigate and solve this issue, the researchers, together with their collaborators at Wuhan University of Technology in China, examined the underlying molecular mechanisms.

Through X-ray diffraction and nuclear magnetic resonance spectroscopy, they identified the need to use ammonium as a volatile cation (positively charged ion) at a critical stage.

Contributing author Dr Sebastian Fürer said, “The presence of ammonium served to drive away the residual acetate during annealing, without forming unwanted side products.”

The researchers hope their work on the fundamental chemistry governing precursor behavior can encourage a greater focus on scalable synthesis and fabrication methods of metal halide perovskite devices.

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Perovskite based solar cells might be a step closer. So far the technology has been just as frustrating as promising. So now a team has innovated another process idea that seems to be workable both in manufacturing and in use. Perhaps this new tech will get some legs and we’ll see.

Argonne National Laboratory scientists explain upgrading the hunt for electrolytes with artificial intelligence that could enable revolutionary battery chemistries.

A new paper published in Science, Meng and colleagues laid out their vision for electrolyte design in future generations of batteries.

Designing a battery is a three-part process. You need a positive electrode, you need a negative electrode, and – for the critical connection – you need an electrolyte that works with both electrodes.

An electrolyte is the battery component that transfers ions – charge-carrying particles – back and forth between the battery’s two electrodes, causing the battery to charge and discharge. For today’s lithium-ion batteries, electrolyte chemistry is relatively well defined. For future generations of batteries being developed around the world and at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, however, the question of electrolyte design is wide open.

Shirley Meng, chief scientist at the Argonne Collaborative Center for Energy Storage Science (ACCESS) and professor of molecular engineering at the Pritzker School of Molecular Engineering of The University of Chicago explained, “While we are locked into a particular concept for electrolytes that will work with today’s commercial batteries, for beyond-lithium-ion batteries the design and development of different electrolytes will be crucial, Electrolyte development is one key to the progress we will achieve in making these cheaper, longer-lasting and more powerful batteries a reality, and taking one major step towards continuing to decarbonize our economy.”

Even relatively small departures from today’s batteries will require a rethinking of electrolyte design, according to Meng. Switching from a nickel-containing oxide to a sulfur-based material as the main constituent of a lithium-ion battery’s positive electrode could yield significant performance benefits and reduce costs if scientists can figure out how to rejigger the electrolyte, she noted.For the other beyond-lithium-ion battery chemistries, like rechargeable sodium-ion or lithium-oxygen, scientists will similarly have to devote considerable attention to the question of the electrolyte.

One major factor that scientists are considering in the development of new electrolytes is how they tend to form an intermediary layer called an interphase, which harnesses the reactivity of the electrodes. “Interphases are crucially important to the functioning of a battery because they control how the selective ions flow into and out of the electrodes,” Meng explained. “Interphases function like a gate to the rest of the battery; if your gate doesn’t function properly, the selective transport doesn’t work.”

The near-term goal, according to the team, is to design electrolytes with the right chemical and electrochemical properties to enable the optimal formation of interphases at both the battery’s positive and negative electrodes. Ultimately, however, researchers believe that they may be able to develop a group of solid electrolytes that would be stable at extreme (both high and low) temperatures and enable batteries with high energy to have much longer lifetimes.

Venkat Srinivasan, director of ACCESS, deputy director of the Joint Center for Energy Storage Research, and co-author on the paper added, “A solid-state electrolyte for an all-solid battery will be a game changer. The key to a solid-state battery is a metal anode, but its performance is currently limited by the formation of needle-like structures called dendrites that can short out the battery. By finding a solid electrolyte that prevents or inhibits dendrite formation, we may be able to realize the benefits of some really exciting battery chemistries.”

In order to speed up their hunt for electrolyte breakthroughs, scientists have turned to the power of advanced characterization and artificial intelligence (AI) to search digitally through many more possible candidates, accelerating what had been a slow and painstaking process of laboratory synthesis. “High performance computing and artificial intelligence are allowing us to identify the best descriptors and characteristics that will enable the tailored design of various electrolytes for specific uses,” Meng said. “Instead of looking at a few dozen electrolyte possibilities a year in the lab, we’re looking at many thousands with the aid of computation.”

“Electrolytes have billions of possible combinations of components – salts, solvents and additives – that we can play with,” Srinivasan said. “To make that number into something more manageable, we’re beginning to really use the power of AI, machine learning and automated laboratories.”

The automated laboratories to which Srinivasan referred will incorporate a robot-driven experimental regime. In this way, machines can perform unassisted ever more carefully refined and calibrated experiments to eventually determine which combination of components will form the perfect electrolyte. “Automated discovery can dramatically increase the power of our research, as machines can work around the clock and reduce the potential for human error,” Srinivasan said.

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That is quite a press release. One does appreciate the back grounding and forward look tied together in a smooth telescoping way.

While artificial intelligence is still just emerging, it is getting really good in some fields where the programming is fairly mature. Battery chemistry might be one, and as the effort to go to an artificial intelligence gets some legs, refinement will get better quickly.

Lets hope this team gets more funding and can show others how to use the path they’re making. We might find out sooner than thought not long ago that battery potential is much higher than we used to think.

University of Michigan scientists developed a new kind of solar panel achieving 9% efficiency in converting water into hydrogen and oxygen – mimicking a crucial step in natural photosynthesis. Outdoors, it represents a major leap in the technology, nearly 10 times more efficient than solar water-splitting experiments of its kind.

But the biggest benefit is driving down the cost of sustainable hydrogen. This is enabled by shrinking the semiconductor, typically the most expensive part of the device. The team’s self-healing semiconductor withstands concentrated light equivalent to 160 suns.

Currently, humans primarily produce hydrogen from the fossil fuel methane, using a great deal of fossil energy in the process. However, plants harvest hydrogen atoms from water using sunlight. As humanity tries to reduce its carbon emissions, hydrogen is attractive as both a standalone fuel and as a component in sustainable fuels made with recycled carbon dioxide. Likewise, it is needed for many chemical processes, producing fertilizers for instance.

Zetian Mi, U-M professor of electrical and computer engineering led the study as reported in the journal in Nature. Mi said, “In the end, we believe that artificial photosynthesis devices will be much more efficient than natural photosynthesis, which will provide a path toward carbon neutrality.”

The outstanding result comes from two advances.

The first is the ability to concentrate the sunlight without destroying the semiconductor that harnesses the light.

Peng Zhou, U-M research fellow in electrical and computer engineering and first author of the study said, “We reduced the size of the semiconductor by more than 100 times compared to some semiconductors only working at low light intensity. Hydrogen produced by our technology could be very cheap.”

The second is using both the higher energy part of the solar spectrum to split water and the lower part of the spectrum to provide heat that encourages the reaction. The magic is enabled by a semiconductor catalyst that improves itself with use, resisting the degradation that such catalysts usually experience when they harness sunlight to drive chemical reactions.

In addition to handling high light intensities, it can thrive in high temperatures that are punishing to computer semiconductors. Higher temperatures speed up the water splitting process, and the extra heat also encourages the hydrogen and oxygen to remain separate rather than renewing their bonds and forming water once more. Both of these helped the team to harvest more hydrogen.

For the outdoor experiment, Zhou set up a lens about the size of a house window to focus sunlight onto an experimental panel just a few inches across. Within that panel, the semiconductor catalyst was covered in a layer of water, bubbling with the hydrogen and oxygen gasses it separated.

The catalyst is made of indium gallium nitride nanostructures, grown onto a silicon surface. That semiconductor wafer captures the light, converting it into free electrons and holes – positively charged gaps left behind when electrons are liberated by the light. The nanostructures are peppered with nanoscale balls of metal, 1/2000th of a millimeter across, that use those electrons and holes to help direct the reaction.

A simple insulating layer atop the panel keeps the temperature at a toasty 75° Celsius, or 167° Fahrenheit, warm enough to help encourage the reaction while also being cool enough for the semiconductor catalyst to perform well. The outdoor version of the experiment, with less reliable sunlight and temperature, achieved 6.1% efficiency at turning the energy from the sun into hydrogen fuel. However, indoors, the system achieved 9% efficiency.

The next challenges the team intends to tackle are to further improve the efficiency and to achieve ultrahigh purity hydrogen that can be directly fed into fuel cells.

Some of the intellectual property related to this work has been licensed to NS Nanotech Inc. and NX Fuels Inc., which were co-founded by Mi. The University of Michigan and Mi have a financial interest in both companies.

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This is quite the improvement! 9% efficiency might be a new record. What is left to answer would be the costs. One would need a lens of some substantial size, likely a lens steering system and a controlled environment to make it “indoor”.

However the economics work out, this plus a super economical means to form up nitrogen fertilizer would be a huge contribution to the world economy. That would save the cost of trying to store the hydrogen thus simplify rapid adoption.

Lets hope the progress continues!


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