GT/ A sustainable battery with a biodegradable electrolyte made from crab shells
Energy & green technology biweekly vol.32, 26th August — 9th September
TL;DR
- Accelerating demand for renewable energy and electric vehicles is sparking a high demand for the batteries that store generated energy and power engines. But the batteries behind these sustainability solutions aren’t always sustainable themselves. Scientists have now create a zinc battery with a biodegradable electrolyte from an unexpected source — crab shells.
- Researchers have solved a key hurdle in greener manufacturing, carbon capture, energy storage and gas purification — using metal oxides.
- Solar cells manufactured from materials known as ‘perovskites’ are catching up with the efficiency of traditional silicon-based solar cells. At the same time, they have advantages of low cost and short energy payback time. However, such solar cells have problems with stability — something that researchers have now managed to solve. The results are a major step forwards in the quest for next-generation solar cells.
- Researchers describe a new wireless laser charging system that overcomes some of the challenges that have hindered previous attempts to develop safe and convenient on-the-go charging systems. With further development, the system could charge mobile devices like phones and laptops at 30 m distances.
- A method to convert a commonly thrown-away plastic to a resin used in 3D-printing could allow for making better use of plastic waste.
- Dye-sensitized solar cells (DSSCs) are a promising next-generation solar power technology, but they suffer from dye aggregation on electrodes, which reduces charge carriers and the conversion efficiency. Fortunately, scientists have now found a simple way to prevent the aggregation by modifying the electrode’s surface with ionic liquids. Stable and eco-friendly, these versatile compounds demonstrate excellent anti-aggregation effects, boosting the performance of DSSCs and opening doors to affordable green energy.
- Researchers have developed a new type of high-efficiency photodetector inspired by the photosynthetic complexes plants use to turn sunlight into energy. Photodetectors are used in cameras, optical communication systems and many other applications to turn photons into electrical signals. The new detector design uses unique quasiparticles known as polaritons to achieve long-range energy transport in an organic material.
- CO2 and methane can be turned into valuable products. But there is a problem with the catalysts required for this: They end up being covered in a layer of carbon, losing their effectivity. A new catalyst has now been developed which solves this problem and can be used for a long time.
- Housing a growing population in homes made out of wood instead of conventional steel and concrete could avoid more than 100 billion tons of emissions of the greenhouse gas CO2 until 2100, a new study shows. These are about 10 percent of the remaining carbon budget for the 2°C climate target. Besides the harvest from natural forests, newly established timber plantations are required for supplying construction wood.
- And more!
Green Technology Market
Green technology is an applicable combination of advanced tools and solutions to conserve natural resources and environment, minimize or mitigate negative impacts from human activities on the environment, and ensure sustainability development. Green technology is also referred to as clean technology or environmental technology which includes technologies, such as IoT, AI, analytics, blockchain, digital twin, security, and cloud, which collect, integrate, and analyze data from various real-time data sources, such as sensors, cameras, and Global Positioning System (GPS).
Green technology, also known as sustainable technology, protects the environment by using various forms of sustainable energy. Some of the best examples of green technologies include solar panels, LED lighting, wind energy, electric vehicles, vertical farming, and composting.
The global Green Technology and Sustainability market size to grow from USD 11.2 billion in 2020 to USD 36.6 billion by 2025, at a Compound Annual Growth Rate (CAGR) of 26.6% during the forecast period. The growing consumer and industrial interest for the use of clean energy resources to conserve environment and increasing use of Radio Frequency Identification sensors across industries are driving the adoption of green technology and sustainability solutions and services in the market.
The blockchain segment is estimated to grow at the highest CAGR: Energy-intensive cryptocurrency mining has caused a spike in carbon emission, and hence blockchain is capable of driving innovation in the field of green technology.
Latest Research
A sustainable chitosan-zinc electrolyte for high-rate zinc-metal batteries
by Meiling Wu, Ye Zhang, Lin Xu, Chunpeng Yang, Min Hong, Mingjin Cui, Bryson C. Clifford, Shuaiming He, Shuangshuang Jing, Yan Yao, Liangbing Hu in Matter
Accelerating demand for renewable energy and electric vehicles is sparking a high demand for the batteries that store generated energy and power engines. But the batteries behind these sustainability solutions aren’t always sustainable themselves. In a paper, scientists create a zinc battery with a biodegradable electrolyte from an unexpected source — crab shells.
“Vast quantities of batteries are being produced and consumed, raising the possibility of environmental problems,” says lead author Liangbing Hu, director of the University of Maryland’s Center for Materials Innovation. “For example, polypropylene and polycarbonate separators, which are widely used in Lithium-ion batteries, take hundreds or thousands of years to degrade and add to environmental burden.”
Batteries use an electrolyte to shuttle ions back and forth between positively and negatively charged terminals. An electrolyte can be a liquid, paste, or gel, and many batteries use flammable or corrosive chemicals for this function. This new battery, which could store power from large-scale wind and solar sources, uses a gel electrolyte made from a biological material called chitosan.
“Chitosan is a derivative product of chitin. Chitin has a lot of sources, including the cell walls of fungi, the exoskeletons of crustaceans, and squid pens,” says Hu. “The most abundant source of chitosan is the exoskeletons of crustaceans, including crabs, shrimps and lobsters, which can be easily obtained from seafood waste. You can find it on your table.”
A biodegradable electrolyte means that about two thirds of the battery could be broken down by microbes — this chitosan electrolyte broke down completely within five months. This leaves behind the metal component, in this case zinc, rather than lead or lithium, which could be recycled.
“Zinc is more abundant in earth’s crust than lithium,” says Hu. “Generally speaking, well-developed zinc batteries are cheaper and safer.” This zinc and chitosan battery has an energy efficiency of 99.7% after 1000 battery cycles, making it a viable option for storing energy generated by wind and solar for transfer to power grids.
Hu and his team hope to continue working on making batteries even more environmentally friendly, including the manufacturing process.
“In the future, I hope all components in batteries are biodegradable,” says Hu. “Not only the material itself but also the fabrication process of biomaterials.”
Precursor engineering of hydrotalcite-derived redox sorbents for reversible and stable thermochemical oxygen storage
by Michael High, Clemens F. Patzschke, Liya Zheng, Dewang Zeng, Oriol Gavalda-Diaz, Nan Ding, Ka Ho Horace Chien, Zili Zhang, George E. Wilson, Andrey V. Berenov, Stephen J. Skinner, Kyra L. Sedransk Campbell, Rui Xiao, Paul S. Fennell, Qilei Song in Nature Communications
Metal oxides are compounds that play a crucial role in processes that reduce carbon dioxide (CO2) emissions. These processes include carbon capture, utilisation and storage (CCUS), purifying and recycling inert gases in solar panel manufacturing, thermochemical energy storage, and producing hydrogen for energy.
These processes are based on reactions where metal oxides gain and lose electrons, known as redox reactions. However, the performance of metal oxides suffers under redox reactions at the high temperatures required for chemical manufacturing. Now, a team led by Imperial College London has developed a new materials design strategy that produces copper-based metal oxides that perform better under high temperatures. The technology is already having a global impact on argon recycling in solar panel manufacturing and is expected to help unleash even more power from existing energy technologies that fight the climate crisis.
Senior author Dr Qilei Song, of Imperial’s Department of Chemical Engineering, said: “As the world transitions to net zero, we need more innovative industrial processes for decarbonisation. To enhance energy security, we must diversify the electricity supply, from renewable energy generation and storage to clean use of fossil fuels with CCUS technologies. Our improved metal oxides hold great potential for use in the energy processes that are helping us reach net zero.”
Metal oxides are key players in a relatively new process called chemical looping combustion (CLC). CLC is an alternative way of burning fossil fuels that uses metal oxides, such as copper oxides, to transport oxygen from the air to react with the fuel. The reaction produces CO2 and steam, which is condensed to allow the efficient capture of CO2 to prevent it entering the atmosphere By capturing the CO2 that is produced, CLC can help people to use fossil fuels in a cleaner way, and is already used in the EU, USA, and China.
However, a key issue that has held back CLC from use on a larger scale is metal oxides’ inability to maintain good oxygen-releasing performance over multiple redox cycles at high temperatures. To solve the problem, the researchers examined the fundamental structures of the metal oxides used in CLC, reasoning that the precursor chemistry to metal oxides was poorly understood, which limited their rational design.
Co-lead author Michael High, PhD candidate at Imperial’s Department of Chemical Engineering, said: “To solve the question of how metal oxides maintain their performance, we looked to the basics of the chemical processes involved in CLC. This is a key example of combining fundamental research and smart design to produce a strategy that’s applicable to a wide range of engineering processes.”
They used an alternative way to engineer the metal oxide structure from a well-known precursor composed of copper-magnesium-aluminium layered double hydroxides (LDHs). By tailoring the chemistry of LDH precursors, researchers found they could produce metal oxides that could still perform well under remarkably high temperatures. They demonstrated this by putting the oxides through 100 chemical cycles in a widely used type of reactor, known as a fluidised bed reactor, for 65 hours.
Their greater ability to withstand heat means that metal oxides produced in this way can be used to unleash more power from purifying and recycling inert gases like argon in manufacturing solar panels, capturing and storing carbon, chemical energy storage, and producing clean hydrogen. To show this, the researchers scaled up the production of metal oxides for use in fluidised bed reactors. They found that creating these materials is simple and readily suitable for upscaling using existing industrial manufacturing methods.
Senior author Professor Paul Fennell, also of the Department of Chemical Engineering, said: “The world must reach net zero carbon emissions by 2050. Renewable energies are developing rapidly, but in the short term we need to develop cost-effective carbon capture technologies that can be applied to decarbonise the industry. Our work will help solve this global challenge.”
Next, the researchers will study the long-term stability of the materials during the combustion of different types of fuels, explore new applications for thermochemical energy storage, and extend the approach to other metal oxide systems for producing clean hydrogen via thermochemical redox cycles.
Improvements in photoelectric performance of dye-sensitised solar cells using ionic liquid-modified TiO2 electrodes
by Tomohiko Inomata, Ayaka Matsunaga, Guangzhu Jin, Takuma Kitagawa, Mizuho Muramatsu, Tomohiro Ozawa, Hideki Masuda in RSC Advances
Solar cells are quickly becoming one of the main ways to produce clean electricity in many countries in the world. Over the past few decades, a tremendous amount of effort has been dedicated to making solar power more prominent. However, the technology currently faces several challenges that limit their widespread application.
In the case of dye-sensitized solar cells (DSSCs) — a highly promising photovoltaic technology — one of the main problems is dye aggregation. By design, DSSCs are electrochemical systems that mimic photosynthesis in plants; they rely on special photosensitive dyes to convert sunlight into electricity. Ideally, the dye should be applied evenly over the surface of an oxide electrode behind a transparent layer so that energy from absorbed sunlight can be transferred easily to the dye’s electrons. This process generates free electrons that power an external circuit. However, most dyes tend to aggregate over the electrode surface in a way that hinders the desired flow of both light and electric charges. This takes a toll on the performance of DSSCs that has proven difficult to overcome.
Fortunately, a team of scientists led by Associate Professor Tomohiko Inomata of Nagoya Institute of Technology, Japan, may have just found a solution to this problem. In their recent study, they showed that certain ionic liquids (molten salts that are in liquid state at relatively low temperatures) can suppress dye aggregation to an impressive degree. Other members of this research team included Ms. Ayaka Matsunaga and Prof. Tomohiro Ozawa from Nagoya Institute of Technology, and Prof. Hideki Masuda from Aichi Institute of Technology, Japan.
But, how do ionic liquids achieve this feat? To shed light on the exact mechanism at play, the researchers focused on two ionic liquids with markedly different molecular sizes and two types of dyes. Both the ionic liquids had a similar molecular structure comprising an anchor that binds well to the electrode (titanium dioxide, TiO2), a main polymer chain linking this anchor to a phosphor atom, and three additional short polymer chains protruding from the phosphor atom and away from the main “vertical” chain.
The researchers submerged the TiO2 electrodes in solutions with different dye-to-ionic-liquid proportions and carefully analyzed how the different molecules adhered to them. After optimizing the synthesis procedure, they found that DSSCs made using the ionic liquid with a longer molecular structure had a remarkably better performance than their counterparts with non-modified oxide electrodes.
“The spatially bulky molecular structure of ionic liquids acts as an effective anti-aggregation agent without significantly impacting the amount of dye adsorbed into the electrode,” explains Dr. Inomata. “Most importantly, the introduction of the larger ionic liquid improves all the photovoltaic parameters of the DSSCs.”
Needless to say, improving solar cell technology could give us an edge in the fight against the ongoing energy and climate crisis. Although ionic liquids are typically expensive, the way it is used by the team is, in fact, cost-effective. “Put simply, the idea is to apply ionic liquids only at the required part of the device — in this case, the electrode’s surface,” states Dr. Inomata.
The team believes that the widespread use of electrodes modified with ionic liquids could pave the way for highly functional yet affordable materials for solar cells and catalytic systems. Since the structure of ionic liquids can be tuned during their synthesis, they offer a much-needed versatility as anti-aggregation agents.
Ion-modulated radical doping of spiro-OMeTAD for more efficient and stable perovskite solar cells
by Tiankai Zhang, Feng Wang, Hak-Beom Kim, In-Woo Choi, et al in Science
Solar cells manufactured from materials known as “perovskites” are catching up with the efficiency of traditional silicon-based solar cells. At the same time, they have advantages of low cost and short energy payback time. However, such solar cells have problems with stability — something that researchers at Linköping University, together with international collaborators, have now managed to solve. The results, published in Science, are a major step forwards in the quest for next-generation solar cells.
“Our results open new possibilities to develop efficient and stable solar cells. Further, they provide new insights into how the doping of organic semiconductors works,” says Feng Gao, professor in the Department of Physics, Chemistry and Biology (IFM) at Linköping University.
Perovskites are crystalline materials with huge potential to contribute to solving the world’s energy shortage. They are cheap to manufacture, with high efficiency and low weight. However, the perovskite solar cells can degrade quickly, and it has not been possible to build high-efficiency perovskite-based solar cells with the required stability.
“There seems to be a trade-off between high efficiency and stability in perovskite-based solar cells. High-efficiency perovskite solar cells tend to show low stability, and vice versa,” says Tiankai Zhang, a postdoc at IFM and one of the principal authors of the article.
When solar energy is converted into electricity in perovskite-based solar cells, one or more charge transport layers are usually needed. These lie directly next to the perovskite layer in the solar cell. The organic charge transport layers often need auxiliary molecules in order to function as intended. The material is described as being “doped.” One doped transport layer called Spiro-OMeTAD is a benchmark in perovskite solar cells, and delivers record power conversion efficiencies. But the present method used to dope Spiro-OMeTAD is slow, and causes the stability issue of perovskite solar cells.
“We have now managed to eliminate the trade-off that has hindered development, using a new doping strategy for Spiro-OMeTAD. This makes it possible for us to obtain both high efficiency and good stability,” says Tiankai Zhang.
Another principal author of the article, Feng Wang, is a junior lecturer at IFM. He points out that perovskite-based solar cells can be used in many ways, and have many areas of applications.
“One advantage of using perovskites is that the solar cells made are thin, which means that they are light and flexible. They can also be semi-transparent. It would be possible, for example, to apply perovskite-based solar cells onto large windows, or building façades. Silicon-based solar cells are too heavy to be used in this way,” says Feng Wang.
Long-range wireless optical power transfer system using an EDFA.
by Nadeem Javed, Ngoc-Luu Nguyen, Syed Farhan Ali Naqvi, Jinyong Ha in Optics Express
Imagine walking into an airport or grocery store and your smartphone automatically starts charging. This could be a reality one day, thanks to a new wireless laser charging system that overcomes some of the challenges that have hindered previous attempts to develop safe and convenient on-the-go charging systems.
“The ability to power devices wirelessly could eliminate the need to carry around power cables for our phones or tablets,” said research team leader Jinyong Ha from Sejong University in South Korea. “It could also power various sensors such as those in Internet of Things (IoT) devices and sensors used for monitoring processes in manufacturing plants.”
The researchers describe their new system, which uses infrared light to safely transfer high levels of power. Laboratory tests showed that it could transfer 400 mW light power over distances of up to 30 meters. This power is sufficient for charging sensors, and with further development, it could be increased to levels necessary to charge mobile devices. Several techniques have been studied for long-range wireless power transfer. However, it has been difficult to safely send enough power over meter-level distances. To overcome this challenge, the researchers optimized a method called distributed laser charging, which has recently gained more attention for this application because it provides safe high-power illumination with less light loss.
“While most other approaches require the receiving device to be in a special charging cradle or to be stationary, distributed laser charging enables self-alignment without tracking processes as long as the transmitter and receiver are in the line of sight of each other,” said Ha. “It also automatically shifts to a safe low power delivery mode if an object or a person blocks the line of sight.”
Distributed laser charging works somewhat like a traditional laser but instead of the optical components of the laser cavity being integrated into one device, they are separated into a transmitter and receiver. When the transmitter and receiver are within a line of sight, a laser cavity is formed between them over the air — or free space — which allows the system to deliver light-based power. If an obstacle cuts the transmitter-receiver line of sight, the system automatically switches to a power-safe mode, achieving hazard-free power delivery in the air
In the new system, the researchers used an erbium-doped fiber amplifier optical power source with a central wavelength of 1550 nm. This wavelength range is in the safest region of the spectrum and poses no danger to human eyes or skin at the power used. Another key component was a wavelength division multiplexing filter that created a narrowband beam with optical power within the safety limits for free space propagation.
“In the receiver unit, we incorporated a spherical ball lens retroreflector to facilitate 360-degree transmitter-receiver alignment, which maximized the power transfer efficiency,” said Ha. “We experimentally observed that the system’s overall performance depended on the refractive index of the ball lens, with a 2.003 refractive index being the most effective.”
To demonstrate the system, the researchers set up a 30-meter separation between a transmitter and a receiver. The transmitter was made of the erbium-doped fiber amplifier optical source, and the receiver unit included a retroreflector, a photovoltaic cell that converts the optical signal to electrical power and an LED that illuminates when power is being delivered. This receiver, which is about 10 by 10 millimeters, could easily be integrated into devices and sensors.
The experimental results showed that a single-channel wireless optical power transfer system could provide an optical power of 400 mW with a channel linewidth of 1 nm over a distance of 30 meters. The photovoltaic converted this to an electrical power of 85 mW. The researchers also showed that the system automatically shifted to a safe power transfer mode when the line of sight was interrupted by a human hand. In this mode, the transmitter produced an incredibly low intensity light that did not pose any risk to people.
“Using the laser charging system to replace power cords in factories could save on maintenance and replacement costs,” said Ha. “This could be particularly useful in harsh environments where electrical connections can cause interference or pose a fire hazard.”
Now that they have demonstrated the system, the researchers are working to make it more practical. For example, the efficiency of the photovoltaic cell could be increased to better convert light into electrical power. They also plan to develop a way to use the system to charge multiple receivers simultaneously.
Photocurrent generation following long-range propagation of organic exciton–polaritons
by Bin Liu, Xinjing Huang, Shaocong Hou, Dejiu Fan, Stephen R. Forrest in Optica
Researchers have developed a new type of high-efficiency photodetector inspired by the photosynthetic complexes plants use to turn sunlight into energy. Photodetectors are used in cameras, optical communication systems and many other applications to turn photons into electrical signals.
“Our devices combine long-range transport of optical energy with long-range conversion to electrical current,” said research team leader Stephen Forrest from the University of Michigan. “This arrangement, analogous to what is seen in plants, has the potential to greatly enhance the power generation efficiency of solar cells, which use devices similar to photodetectors to convert sunlight into energy.”
The photosynthetic complexes found in many plants consist of a large light absorbing region that delivers molecular excited state energy to a reaction center where the energy is converted to a charge. While this setup is very efficient, mimicking it requires achieving long-range energy transport in an organic material, which has proven difficult to accomplish. To achieve this seemingly impossible task, the researchers used unique quasiparticles known as polaritons. Forrest and colleagues report their new detector, which generates polaritons in an organic thin film.
“A polariton combines a molecular excited state with a photon, giving it both light-like and matter-like properties that allow long-range energy transport and conversion,” said Forrest. “This photodetector is one of the first demonstrations of a practical optoelectronic device based on polaritons.”
The researchers envisioned the new detector several years ago while looking for ways to make better solar cells. “After observing polariton propagation over long distances in simple structures such as a mirror with an organic film on its surface, we thought it might be possible to make a photosynthetic analog using polaritons,” said Forrest. “However, it was quite difficult to figure out how to build such a device.” To create a photodetector based on polaritons, the researchers had to design structures that allow polariton propagation over long distances in an organic semiconductor thin film. They also had to figure out how to integrate a simple organic detector into the propagation region in a way that would produce efficient polariton-to-charge conversion.
“We borrowed from structures that we previously designed to create efficient organic photovoltaic cells,” said Forrest. “It was a bit fortuitous that these structures allowed efficient harvesting of the energy carried by polaritons. Polaritons still hold some mysteries, and this is a new way of using them, so we weren’t sure if it would work.”
The researchers analyzed their new device by using a special Fourier plane microscope to observe polariton propagation. Due to the unusual structure of the detector they had to develop a way to accurately quantify the results and put them in the context of conventional detectors well known to the optics community. The results showed that the new photodetector is more efficient at converting light to electrical current than a comparable silicon photodiode. It can also gather light from areas about 0.01 mm2 and achieve conversion of light to electrical current over exceptionally long distances of 0.1 nm. This distance is three orders larger than the energy transfer distance of photosynthetic complexes. Until now, most polaritons have been observed as stationary quasiparticles in closed cavities with highly reflective mirrors on both top and bottom. The new work revealed important insights into how polaritons propagate in open structures with a single mirror. The new device also allowed the first measurements of how efficiently incident photons can be converted to polaritons.
“Our work shows that polaritons, in addition to being interesting science, are also a goldmine of applications yet to be discovered,” said Forrest. “Devices such as ours provide an unusual, and possibly unique, method to understand the fundamental properties of polaritons and to enable yet to be imagined ways to manipulate light and charge.”
A chemical approach for the future of PLA upcycling: from plastic wastes to new 3D printing materials
by Lin Shao, Yu-Chung Chang, Cheng Hao, Ming-en Fei, Baoming Zhao, Brian J. Bliss, Jinwen Zhang in Green Chemistry
A method to convert a commonly thrown-away plastic to a resin used in 3D-printing could allow for making better use of plastic waste.
A team of Washington State University researchers developed a simple and efficient way to convert polylactic acid (PLA), a bio-based plastic used in products such as filament, plastic silverware and food packaging to a high-quality resin.
“We found a way to immediately turn this into something that’s stronger and better, and we hope that will provide people the incentive to upcycle this stuff instead of just toss it away,” said Yu-Chung Chang, a postdoctoral researcher in the WSU School of Mechanical and Materials Engineering and a co-corresponding author on the work. “We made stronger materials just straight out of trash. We believe this could be a great opportunity.”
About 300,000 tons of PLA are produced annually, and its use is increasing dramatically. Although it’s bio-based, PLA, which is categorized as a number seven plastic, doesn’t break down easily. It can float in fresh or salt water for a year without degrading. It is also rarely recycled because like many plastics, when it’s melted down and re-formed, it doesn’t perform as well as the original version and becomes less valuable.
“It’s biodegradable and compostable, but once you look into it, it turns out that it can take up to 100 years for it to decompose in a landfill,” Chang said. “In reality, it still creates a lot of pollution. We want to make sure that when we do start producing PLA on the million-tons scale, we will know how to deal with it.”
In their study, the researchers, led by Professor Jinwen Zhang in the School of Mechanical and Materials Engineering, developed a fast and catalyst-free method to recycle the PLA, breaking the long chain of molecules down into simple monomers — the building blocks for many plastics. The entire chemical process can be done at mild temperatures in about two days. The chemical they used to break down the PLA, aminoethanol, is also inexpensive.
“If you want to rebuild a Lego castle into a car, you have to break it down brick by brick,” Chang said. “That’s what we did. The aminoethanol precision-cut the PLA back to a monomer, and once it’s back to a monomer, the sky’s the limit because you can re-polymerize it into something stronger.”
Once the PLA was broken down to its basic building blocks, the researchers rebuilt the plastic and created a type of photo-curable liquid resin that is commonly used as printing “ink” for 3D printers. When it was used in a 3D printer and cured into plastic pieces, the product showed equal or better mechanical and thermal properties than commercially available resins. While the researchers focused on PLA for the study, they hope to apply the work to polyethylene terephthalate (PET), which is more common than PLA, has a similar chemical structure and presents a bigger waste problem.
Impact of nanoparticle exsolution on dry reforming of methane: Improving catalytic activity by reductive pre-treatment of perovskite-type catalysts
by F. Schrenk, L. Lindenthal, H. Drexler, G. Urban, R. Rameshan, H. Summerer, T. Berger, T. Ruh, A.K. Opitz, C. Rameshan in Applied Catalysis B: Environmental
Wherever the production of harmful greenhouse gases cannot be prevented, they should be converted into something useful: this approach is called “carbon capture and utilisation.” Special catalysts are needed for this. Until now, however, the problem has been that a layer of carbon quickly forms on these catalysts — this is called “coking” — and the catalyst loses its effect. At TU Wien, a new approach was taken: tiny metallic nanoparticles were produced on perovskite crystals through special pre-treatment. The interaction between the crystal surface and the nanoparticles then ensures that the desired chemical reaction takes place without the dreaded coking effect.
Carbon dioxide (CO2) and methane are the two human-made greenhouse gases that contribute most to climate change. Both gases often occur in combination, for example in biogas plants.
“So-called methane dry reforming is a method that can be used to convert both gases into useful synthesis gas at the same time,” says Prof. Christoph Rameshan from the Institute of Materials Chemistry at TU Wien. “Methane and carbon dioxide are turned into hydrogen and carbon monoxide — and it is then relatively easy to produce other hydrocarbons from them, right up to biofuels.”
The big problem here is the stability of the catalysts: “The metal catalysts that have been used for this process so far tend to produce tiny carbon nanotubes,” explains Florian Schrenk, who is currently working on his dissertation in Rameshan’s team. These nanotubes deposit as a black film on the surface of the catalyst and block it.
The TU Wien team has now created a catalyst with fundamentally different properties: “We use perovskites, which are crystals containing oxygen, which can be doped with various metal atoms,” says Christoph Rameshan. “You can insert nickel or cobalt, for example, into the perovskite — metals that have also been used in catalysis before.”
A special pre-treatment of the crystal with hydrogen at around 600 °C allows the nickel or cobalt atoms to migrate to the surface and form nanoparticles there. The size of the nanoparticles is crucial: Success has been achieved with nanoparticles with a diameter of 30 to 50 nanometres. The desired chemical reaction then takes place on these tiny grains, but at the same time the oxygen contained in the perovskite prevents the formation of carbon nanotubes.
“We were able to show in our experiments: If you choose the right size of nanoparticles, no carbon film is created — coking is no longer a danger,” says Florian Schrenk. “Moreover, the nanoparticles are stable, the structure of the catalyst does not change, it can be used permanently.”
The novel perovskite catalysts could be used wherever methane and carbon dioxide are produced simultaneously — this is often the case when dealing with biological substances, for example in biogas plants. Depending on the selected reaction temperature, one can influence the composition of the resulting synthesis gas. In this way, the further processing of climate-damaging greenhouse gases into valuable products could become an important building block for a sustainable circular economy.
Land use change and carbon emissions of a transformation to timber cities
by Abhijeet Mishra, Florian Humpenöder, Galina Churkina, Christopher P. O. Reyer, Felicitas Beier, Benjamin Leon Bodirsky, Hans Joachim Schellnhuber, Hermann Lotze-Campen, Alexander Popp in Nature Communications
Housing a growing population in homes made out of wood instead of conventional steel and concrete could avoid more than 100 billion tons of emissions of the greenhouse gas CO2 until 2100, a new study by the Potsdam Institute for Climate Impact Research shows. These are about 10 percent of the remaining carbon budget for the 2°C climate target. Besides the harvest from natural forests, newly established timber plantations are required for supplying construction wood. While this does not interfere with food production, a loss of biodiversity may occur if not carefully managed, according to the scientists. The study is the first to analyze the impacts of a large-scale transition to timber cities on land use, land-use change emissions, and long-term carbon storage in harvested wood products.
“More than half the world’s population currently lives in cities, and by 2100 this number will increase significantly. This means more homes will be built with steel and concrete, most of which have a serious carbon footprint,” says Abhijeet Mishra, scientist from the Potsdam Institute for Climate Impact Research (PIK) and lead author of the study. “But we have an alternative: We can house the new urban population in mid-rise buildings — that is 4 to 12 stories — made out of wood.”
Wood is known as a renewable resource that carries the lowest carbon footprint of any comparable building material as the trees take up CO2 from the atmosphere to grow. Mishra explains: “Production of engineered wood releases much less CO2 than production of steel and cement. Engineered wood also stores carbon, making timber cities a unique long-term carbon sink — by 2100, this could save more than 100Gt of additional CO2 emissions, equivalent to 10% of the remaining carbon budget for the 2°C target.”
In the paper, with the help of the open-source global land use allocation model MAgPIE, the scientists looked at four different land-use scenarios: One with conventional building materials like cement and steel, three with additional timber demand on top of the regular timber demand. They also analysed how the additional high demand for wooden construction materials could be satisfied, where it could come from and what the consequences could be in direct and indirect carbon emissions from land-use.
“Our simulation shows that sufficient wood for new mid-rise urban buildings can be produced without major repercussion on food production,” explains PIK scientist Florian Humpenöder, co-author of the study. “Wood is sourced from timber plantations as well as natural forests. Most of the additional timber plantations needed — we are talking about roughly 140 million hectares — are established on harvested forest areas and thus not at the cost of agricultural land,” as Humpenöder underlines. “We need farm land to grow food for the people — using it to grow trees could potentially cause competition for the limited land resources.”
The scientists also looked at biodiversity impacts that occur when natural ecosystems are replaced with timber plantations. Alexander Popp, head of the landuse management group at PIK scientist and co-author of the study, explains: “The question of how and from where to source the wood for the construction of timber cities is crucial. In our computer simulations, we have set a clear limit to timber extraction and for adding new tree plantations: Nothing can be cut off in pristine forests and biodiversity conservation areas.” In fact, Popp underlines: “The explicit safeguarding of these protected areas is key, but still, the establishment of timber plantations at the cost of other non-protected natural areas could thereby further increase a future loss of biodiversity.” Other studies indicate that measures such as a transition to healthy diets with less meat consumption could help to free-up land for wood and food production while conserving biodiversity.
Mishra concludes: “Our study underlines that urban homes made out of wood could play a vital role in climate change mitigation due to their long-term carbon storage potential. Strong governance and careful planning are required to limit negative impacts on biodiversity and to ensure a sustainable transition to timber cities.”
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