GT/ Clean fuels made ‘from thin air’ and plastic waste
Energy & green technology biweekly vol.52, 22nd June — 7th July
TL;DR
- Researchers have demonstrated how carbon dioxide can be captured from industrial processes — or even directly from the air — and transformed into clean, sustainable fuels using just the energy from the Sun.
- New carbon capture technology can generate a continuous, high-purity carbon dioxide stream from diluted, or low-concentration, gas streams using only electricity and a water-and-oxygen-based reaction.
- Perovskite solar cells have attained now attained an extremely high-efficiency rate of 24.35% with an active area of 1 cm2. This ground-breaking achievement in maximizing power generation from next-generation renewable energy sources will be crucial to securing the world’s energy future.
- Demand for modern biofuels is expected to grow substantially in order to mitigate climate emissions. However, they are far from being a climate-neutral alternative to gasoline and diesel. A new study shows that under current land-use regulations, CO2 emission factors for biofuels might even exceed those for fossil diesel combustion due to large-scale land clearing related to growing biomass. Before bioenergy can effectively contribute to achieving carbon neutrality, international agreements need to ensure the effective protection of forests and other natural lands by introducing carbon pricing, the expert team argues.
- Tidal range schemes are financially viable and could lower energy bills say researchers. The research combined a tidal range power generation model with its cost model to demonstrate the viability of tidal power. The study demonstrates the benefits of tidal energy, which does not suffer from unpredictable intermittency as power is generated both day and night and in windy or calm weather. The creation of a tidal barrage could operate for 120 years or more to meet future demand and storage problems.
- The quest to develop hydrogen as a clean energy source that could curb our dependence on fossil fuels may lead to an unexpected place — coal. Scientists have found that coal may represent a potential way to store hydrogen gas, much like batteries store energy for future use, addressing a major hurdle in developing a clean energy supply chain.
- When it comes to supplying energy for space exploration and settlements, commonly available solar cells made of silicon or gallium arsenide are still too heavy to be feasibly transported by rocket. To address this challenge, a wide variety of lightweight alternatives are being explored, including solar cells made of a thin layer of molybdenum selenide, which fall into the broader category of 2D transition metal dichalcogenide (2D TMDC) solar cells. Researchers propose a device design that can take the efficiencies of 2D TMDC devices from 5%, as has already been demonstrated, to 12%.
- Researchers are exploring the different ways of harvesting materials from water.
- A new class of materials that can absorb low-energy light and transform it into higher-energy light might lead to more efficient solar panels, more accurate medical imaging, and better night vision goggles.
- A team of researchers has created a new supply chain model which could empower the international hydrogen renewable energy industry.
- 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
Integrated capture and solar-driven utilization of CO2 from flue gas and air
by Sayan Kar, Motiar Rahaman, Virgil Andrei, Subhajit Bhattacharjee, Souvik Roy, Erwin Reisner in Joule
Researchers have demonstrated how carbon dioxide can be captured from industrial processes — or even directly from the air — and transformed into clean, sustainable fuels using just the energy from the Sun.
The researchers, from the University of Cambridge, developed a solar-powered reactor that converts captured CO2 and plastic waste into sustainable fuels and other valuable chemical products. In tests, CO2 was converted into syngas, a key building block for sustainable liquid fuels, and plastic bottles were converted into glycolic acid, which is widely used in the cosmetics industry.
Unlike earlier tests of their solar fuels technology however, the team took CO2 from real-world sources — such as industrial exhaust or the air itself. The researchers were able to capture and concentrate the CO2 and convert it into sustainable fuel. Although improvements are needed before this technology can be used at an industrial scale, the results represent another important step toward the production of clean fuels to power the economy, without the need for environmentally destructive oil and gas extraction.
For several years, Professor Erwin Reisner’s research group, based in the Yusuf Hamied Department of Chemistry, has been developing sustainable, net-zero carbon fuels inspired by photosynthesis — the process by which plants convert sunlight into food — using artificial leaves. These artificial leaves convert CO2 and water into fuels using just the power of the sun. To date, their solar-driven experiments have used pure, concentrated CO2 from a cylinder, but for the technology to be of practical use, it needs to be able to actively capture CO2 from industrial processes, or directly from the air. However, since CO2 is just one of many types of molecules in the air we breathe, making this technology selective enough to convert highly diluted CO2 is a huge technical challenge.
“We’re not just interested in decarbonisation, but de-fossilisation — we need to completely eliminate fossil fuels in order to create a truly circular economy,” said Reisner. “In the medium term, this technology could help reduce carbon emissions by capturing them from industry and turning them into something useful, but ultimately, we need to cut fossil fuels out of the equation entirely and capture CO2 from the air.”
The researchers took their inspiration from carbon capture and storage (CCS), where CO2 is captured and then pumped and stored underground.
“CCS is a technology that’s popular with the fossil fuel industry as a way to reduce carbon emissions while continuing oil and gas exploration,” said Reisner. “But if instead of carbon capture and storage, we had carbon capture and utilisation, we could make something useful from CO2 instead of burying it underground, with unknown long-term consequences, and eliminate the use of fossil fuels.”
The researchers adapted their solar-driven technology so that it works with flue gas or directly from the air, converting CO2 and plastics into fuel and chemicals using only the power of the sun. By bubbling air through the system containing an alkaline solution, the CO2 selectively gets trapped, and the other gases present in air, such as nitrogen and oxygen, harmlessly bubble out. This bubbling process allows the researchers to concentrate the CO2 from air in solution, making it easier to work with.
The integrated system contains a photocathode and an anode. The system has two compartments: on one side is captured CO2 solution that gets converted into syngas, a simple fuel. On the other plastics are converted into useful chemicals using only sunlight.
“The plastic component is an important trick to this system,” said co-first author Dr Motiar Rahaman. “Capturing and using CO2 from the air makes the chemistry more difficult. But, if we add plastic waste to the system, the plastic donates electrons to the CO2. The plastic breaks down to glycolic acid, which is widely used in the cosmetics industry, and the CO2 is converted into syngas, which is a simple fuel.”
“This solar-powered system takes two harmful waste products — plastic and carbon emissions — and converts them into something truly useful,” said co-first author Dr Sayan Kar.
“Instead of storing CO2 underground, like in CCS, we can capture it from the air and make clean fuel from it,” said Rahaman. “This way, we can cut out the fossil fuel industry from the process of fuel production, which can hopefully help us avoid climate destruction.”
“The fact that we can effectively take CO2 from air and make something useful from it is special,” said Kar. “It’s satisfying to see that we can actually do it using only sunlight.”
The scientists are currently working on a bench-top demonstrator device with improved efficiency and practicality to highlight the benefits of coupling direct air capture with CO2 utilisation as a path to a zero-carbon future.
Continuous carbon capture in an electrochemical solid-electrolyte reactor
by Peng Zhu, Zhen-Yu Wu, Ahmad Elgazzar, Changxin Dong, Tae-Ung Wi, Feng-Yang Chen, Yang Xia, Yuge Feng, Mohsen Shakouri, Jung Yoon Kim, Zhiwei Fang, T. Alan Hatton, Haotian Wang in Nature
New technology developed by Rice University engineers could lower the cost of capturing carbon dioxide from all types of emissions, a potential game-changer for both industries looking to adapt to evolving greenhouse gas standards and for the emergent energy-transition economy.
According to a study, the system from the lab of chemical and biomolecular engineer Haotian Wang can directly remove carbon dioxide from sources ranging from flue gas to the atmosphere by using electricity to induce a water-and-oxygen-based electrochemical reaction. This technological feat could turn direct air capture from fringe industry ⎯ there are only 18 plants currently in operation worldwide ⎯ into a promising front for climate change mitigation. Most carbon-capture systems involve a two-step process: First, high-pH liquids are used to separate the carbon dioxide, which is acidic, from mixed-gas streams such as flue gas. Next, the carbon dioxide is regenerated from the solution through heating or by injecting a low-pH liquid.
“Once the carbon dioxide is trapped in these solvents, you have to regenerate it,” Wang said. “Traditional amine scrubbing methods require temperatures of 100–200 degrees Celsius (212–392 Fahrenheit). For calcium carbonate-based processes you need temperatures as high as 900 Celsius (1652 Fahrenheit).
“There are literally no chemicals produced or consumed with our process. We also don’t need to heat up or pressurize our device, we just need to plug it into a power outlet and it will work.”
Another drawback of current carbon-capture technologies is their reliance on large-scale, centralized infrastructure. By contrast, the system developed in the Wang lab is a scalable, modular, point-of-use concept that can be adapted to a variety of scenarios.
“The technology can be scaled up to industrial settings ⎯ power plants, chemical plants ⎯ but the great thing about it is that it allows for small-scale use as well: I can even use it in my office,” Wang said. “We could, for example, pull carbon dioxide from the atmosphere and continuously inject that concentrated gas into a greenhouse to stimulate plant growth. We’ve heard from space technology companies interested in using the device on space stations to remove the carbon dioxide astronauts exhale.”
The reactor developed by Wang and his team can continuously remove carbon dioxide from a simulated flue gas with efficiency above 98% using a relatively low electricity input.
“The electricity used to power a 50-watt lightbulb for an hour will yield 10 to 25 liters of high-purity carbon dioxide,” said Peng Zhu, a chemical and biomolecular engineering graduate student and lead author on the study.
Wang noted that the process has “no carbon footprint or a very limited footprint” if powered by electricity from renewable sources such as solar or wind.
“This is great news considering that renewable electricity is becoming more and more cost-effective,” Wang said.
The reactor consists of a cathode set up to perform oxygen reduction, an oxygen evolution reaction-performing anode and a compact yet porous solid-electrolyte layer that allows efficient ion conduction. An earlier version of the reactor was used to reduce carbon dioxide into pure liquid fuels and reduce oxygen into pure hydrogen peroxide solutions.
“Previously, our group focused mainly on carbon dioxide utilization,” Zhu said. “We worked on producing pure liquid products like acetic acid, formic acid, etc.”
According to Wang, Zhu observed during the research process that gas bubbles flowed out of the reactor’s middle chamber along with the liquids.
“At the beginning, we didn’t pay a lot of attention to this phenomenon,” Wang said. “However, Peng observed that if we applied more current there were more bubbles. That’s a direct correlation, which means that something not random is happening.”
The researchers realized that the alkaline interface generated during reduction reactions at the reactor’s cathode side interacted with carbon dioxide molecules to form carbonate ions . The carbonate ions migrate into the reactor’s solid-electrolyte layer where they combine with protons resulting from water oxidation at the anode side, forming a continuous flow of high-purity carbon dioxide.
“We randomly discovered this phenomenon during our previous studies,” Wang said. “We then tuned and optimized the technology for this new project and new application. We’ve spent years of continuous work on this type of electrochemical device.
“Scientific discovery often requires this patient, continuous observation and the curiosity to learn what’s really going on, the choice not to neglect those phenomena that don’t necessarily fit in the experimental frame.”
Solar cell efficiency tables
by Martin A. Green, Ewan D. Dunlop, Masahiro Yoshita, Nikos Kopidakis, Karsten Bothe, Gerald Siefer, Xiaojing Hao in Progress in Photovoltaics Research and Applications
Perovskite solar cells designed by a team of scientists from the National University of Singapore (NUS) have attained a world record efficiency of 24.35% with an active area of 1 cm2. This achievement paves the way for cheaper, more efficient and durable solar cells.
To facilitate consistent comparisons and benchmarking of different solar cell technologies, the photovoltaic (PV) community uses a standard size of at least 1 cm2 to report the efficiency of one-sun solar cells. Prior to the record-breaking feat by the NUS team, the best 1-cm2 perovskite solar cell recorded a power conversion efficiency of 23.7%. This ground-breaking achievement in maximising power generation from next-generation renewable energy sources will be crucial to securing world’s energy future.
Perovskites are a class of materials that exhibit high light absorption efficiency and ease of fabrication, making them promising for solar cell applications. In the past decade, perovskite solar cell technology has achieved several breakthroughs, and the technology continues to evolve.
“To address this challenge, we undertook a dedicated effort to develop innovative and scalable technologies aimed at improving the efficiency of 1-cm2 perovskite solar cells. Our objective was to bridge the efficiency gap and unlock the full potential of larger-sized devices,” said Assistant Professor Hou Yi, leader of the NUS research team comprising scientists from the Department of Chemical and Biomolecular Engineering under the NUS College of Design and Engineering as well as the Solar Energy Research Institute of Singapore (SERIS), a university-level research institute in NUS.
He added, “Building on more than 14 years of perovskite solar cell development, this work represents the first instance of an inverted-structure perovskite solar cell exceeding the normal structured perovskite solar cells with an active area of 1 cm2, and this is mainly attributed to the innovative charge transporting material incorporated in our perovskite solar cells. Since inverted-structure perovskite solar cells always offer excellent stability and scalability, achieving a higher efficiency than for normal-structured perovskite cells represents a significant milestone in commercialising this cutting-edge technology.”
The record-breaking accomplishment was made by successfully incorporating a novel interface material into perovskite solar cells.
“The introduction of this novel interface material brings forth a range of advantageous attributes, including excellent optical, electrical, and chemical properties. These properties work synergistically to enhance both the efficiency and longevity of perovskite solar cells, paving the way for significant improvements in their performance and durability,” explained team member Dr Li Jia, postdoctoral researcher at SERIS.
The promising results reported by the NUS team mark a pivotal milestone in advancing the commercialisation of a low-cost, efficient, stable perovskite solar cell technology. “Our findings set the stage for the accelerated commercialisation and integration of solar cells into various energy systems. We are excited by the prospects of our invention that represents a major contribution to a sustainable and renewable energy future,” said team member Mr Wang Xi, an NUS doctoral student.
Building upon this exciting development, Asst Prof Hou and his team aim to push the boundaries of perovskite solar cell technology even further. Another key area of focus is to improve the stability of perovskite solar cells, as perovskite materials are sensitive to moisture and can degrade over time. Asst Prof Hou commented, “We are developing a customised accelerating aging methodology to bring this technology from the lab to the fab. One of our next goals is to deliver perovskite solar cells with 25 years of operational stability.” The team is also working to scale up the solar cells to modules by expanding the dimensions of the perovskite solar cells and demonstrating their viability and effectiveness on a larger scale.
“The insights gained from our current study will serve as a roadmap for developing stable, and eventually, commercially-viable perovskite solar cell products that can serve as sustainable energy solutions to help reduce our reliance on fossil fuels,” Asst Prof Hou added.
Bioenergy-induced land-use-change emissions with sectorally fragmented policies
by Leon Merfort, Nico Bauer, Florian Humpenöder, David Klein, Jessica Strefler, Alexander Popp, Gunnar Luderer, Elmar Kriegler in Nature Climate Change
Demand for modern biofuels is expected to grow substantially in order to mitigate climate emissions. However, they are far from being a climate neutral alternative to gasoline and diesel. A new study shows that under current land-use regulations, CO2 emission factors for biofuels might even exceed those for fossil diesel combustion due to large-scale land clearing related to growing biomass. Before bioenergy can effectively contribute to achieving carbon neutrality, international agreements need to ensure the effective protection of forests and other natural lands by introducing carbon pricing, the expert team from the Potsdam Institute for Climate Impact Research (PIK) argues.
“Our results show: The state of current global land regulation is inadequate to control land-use-change emissions from modern biofuels,” lead author Leon Merfort explains. “If cultivation for bioenergy grasses is not strictly limited to marginal or abandoned land, food production could shift and agricultural land use expand into natural land. This would cause substantial carbon dioxide emissions due to forest clearing in regions with weak or no land regulation.” These indirect effects of bioenergy use are a challenge for policy makers, as food and bioenergy markets are globally connected but beyond the control of individual national policies. Tragically, the regulatory gap in the land-use sector would keep bioenergy supply cheap, while pushing the energy sector to phase-out fossil fuels even faster to compensate for additional emissions from land-use change. This spiral in turn increases the demand for bioenergy.
To investigate the implications of bioenergy induced land-use change emissions under sectorally fragmented policies, the researchers coupled energy and land system models to derive alternative transformation pathways consistent with limiting global warming to well below 2 °C. These pathways include varying assumptions on land-use and energy policies, as these have a large influence on CO2 emissions from land-use change and also affect the amount of bioenergy used to fulfill the global energy demand. By comparing these scenarios with a corresponding counterfactual scenario with no bioenergy production and hence lower land-use-change emissions, the researchers were able to derive emission factors, which attribute CO2 emissions from land-use change to bioenergy production in the light of different policy frameworks.
“We find that without additional land-use regulation, land clearing related to the production of modern biofuels results in CO2 emission factors — averaged over a 30-year period — that are higher than those from burning fossil diesel,” co-author Florian Humpenöder says. These results underline the need for a paradigm shift in land-use policy. “Our results show that a globally comprehensive land protection or carbon pricing scheme would avoid high CO2 emissions from land-use change related to the production of modern biomass.”
“Phasing out fossil fuels will generate demands of bioenergy worth hundreds of billions of Dollars by mid-century ,” co-author Nico Bauer highlights. “The agricultural sector will try to take advantage of these new opportunities, but potential expansion into high-yield areas often coincides with high upfront CO2 emissions from land conversion. Only reducing the demand for bioenergy will not solve this problem. Surprisingly, we also find that the protection of 90% of all global forest areas is not enough because the remaining 10% would still be too big of a loophole.”
Crucial is not the price level itself, but the comprehensiveness to cover near 100% of all forests and other natural lands, the research team finds. Pricing all emissions from land-use change with only 20% of the CO2 price in the energy system is more effective than a protection scheme covering 90% of all forests globally. The protection of carbon stored in existing forests should be placed high on the international policy agenda as fossil fuel phase-out progresses and regulations in the land-use sector lag behind, Bauer stresses: “Our results show that bioenergy can be produced with limited emissions under effective land-use regulations. Yet, if the regulatory gap remains wide open, bioenergy will not be part of the solution to mitigate climate change, but part of the problem.”
Tidal range generation: combining the Lancaster zero-dimension generation and cost models
by David Vandercruyssen, Simon Baker, David Howard, George Aggidis in Proceedings of the Institution of Civil Engineers — Energy
Tidal range schemes are financially viable and could lower energy bills say researchers.
Research by Lancaster University’s School of Engineering and the UK Centre for Ecology and Hydrology combined a tidal range power generation model with its cost model to demonstrate the viability of tidal power.
Professor George Aggidis, Head of Energy Engineering at Lancaster University, said: “The obvious question for the UK, with one of the best tidal resources globally, is why haven’t we already got a tidal barrage scheme?”
The research demonstrates the benefits of tidal energy, which does not suffer from unpredictable intermittency as power is generated both day and night. The creation of a tidal barrage could operate for 120 years or more to meet future demand and storage problems.
Professor Aggidis said: “There is an urgent need to kick-start the selection and development of schemes around Britain. Tidal range generation is predictable renewable energy driven by the gravitational pull of the moon and sun. The environmental and economic benefits are huge as barrages can protect coastal areas from flooding and sea level rise. With two-way generation and pumping, the full range of existing tides can be maintained within impoundments to protect and support low-lying intertidal areas such as saltmarshes and mudflats.
Our studies show that with modern technology and operating procedures, estuarine barrages are the only practical way to protect these vital habitats. Coastal lagoons have also been proposed for several locations around Britain’s coast. Schemes will provide jobs in construction and manufacturing for generations to come as well as opportunities for transport, communication, conservation, and recreation. In the long-term they will provide reliable power with reduced costs.”
The UK has the second highest tidal range in the world and offers the UK a level of independence from global prices and in the long-term cheap clean power.
Hydrogen sorption and diffusion in coals: Implications for hydrogen geo-storage
by Ang Liu, Shimin Liu in Applied Energy
The quest to develop hydrogen as a clean energy source that could curb our dependence on fossil fuels may lead to an unexpected place — coal. A team of Penn State scientists found that coal may represent a potential way to store hydrogen gas, much like batteries store energy for future use, addressing a major hurdle in developing a clean energy supply chain.
“We found that coal can be this geological hydrogen battery,” said Shimin Liu, associate professor of energy and mineral engineering at Penn State. “You could inject and store the hydrogen energy and have it there when you need to use it.”
Hydrogen is a clean burning fuel and shows promise for use in the most energy intensive sectors of our economy — transportation, electricity generation and manufacturing. But much work remains to build a hydrogen infrastructure and make it an affordable and reliable energy source, the scientists said. This includes developing a way to store hydrogen, which is currently expensive and inefficient. Geologic formations are an intriguing option, the scientists said, because they can store large amounts of hydrogen to meet the peaks and valleys as energy demand changes daily or seasonally.
“Coal is well-studied, and we have been commercially producing gas from coal for almost a half century,” Liu said. “We understand it. We have the infrastructure. I think coal would be the logical place to do geological hydrogen storage.”
To put this to the test, the scientists analyzed eight types of coals from coalfields across the United States to better understand their sorption and diffusion potential, or how much hydrogen they can hold. All eight coals showed considerable sorption properties, with low-volatile bituminous coal from eastern Virgina and anthracite coal from eastern Pennsylvania performing the best in tests, the scientists reported in the journal Applied Energy.
“I think it’s highly possible that coal could be the very top selection for geological storage from a scientific perspective,” said Liu. “We find that coal outperforms other formations because it can hold more, it has existing infrastructure and is widely available across the country and near populated areas.”
Depleted coalbed methane reservoirs may be the best candidates. These seams contain unconventional natural gas like methane and have become an important source of fossil fuel energy over the last several decades. The methane sticks to the surface of the coal, in a process called adsorption. Similarly, injecting hydrogen into coal would cause that gas to absorb or stick to the coal. These formations often have a layer of shale or mudstone on top that act as a seal keeping methane, or in this case hydrogen, sealed until it is needed and pumped back out, the scientists said.
“A lot of people define coal as a rock, but it’s really a polymer,” Liu said. “It has high carbon content with a lot of small pores that can store much more gas. So coal is like a sponge that can hold many more hydrogen molecules compared to other non-carbon materials.”
The scientists designed special equipment to conduct the experiments. Coal has a weaker affinity with hydrogen compared to other sorbing gases like methane and carbon dioxide, so traditional pressurized equipment for determining sorption would not have worked.
“We did a very novel and very challenging design,” Liu said. “It took years to figure out how to do this properly. We had to properly design an experiment system, trial and error based on our previous experience with coals and shales.”
Based on their results, the scientists determined anthracite and semi-anthracite coals are good candidates for hydrogen storage in depleted coal seams, and low-volatile bituminous coal are better candidates for gassy coal seams. Developing hydrogen storage in coal mining communities could bring new economic opportunities to these regions while also helping create the nation’s hydrogen infrastructure.
“In the energy transition, it’s really coal communities that have been the most impacted economically,” Liu said. “This is certainly an opportunity to repurpose the coal region. They already have the expertise — the energy engineer and skills. If we can build an infrastructure and change their economic opportunities — I think that’s something we should consider.”
How Good Can 2D Excitonic Solar Cells Be?
by Zekun Hu, Da Lin, Jason Lynch, Kevin Xu, Deep Jariwala in Device
When it comes to supplying energy for space exploration and settlements, commonly available solar cells made of silicon or gallium arsenide are still too heavy to be feasibly transported by rocket. To address this challenge, a wide variety of lightweight alternatives are being explored, including solar cells made of a thin layer of molybdenum selenide, which fall into the broader category of 2D transition metal dichalcogenide (2D TMDC) solar cells. Researchers propose a device design that can take the efficiencies of 2D TMDC devices from 5%, as has already been demonstrated, to 12%.
“I think people are slowly coming to the realization that 2D TMDCs are excellent photovoltaic materials, though not for terrestrial applications, but for applications that are mobile — more flexible, like space-based applications,” says lead author. “The weight of 2D TMDC solar cells is 100 times less than silicon or gallium arsenide solar cells, so suddenly these cells become a very appealing technology.”
While 2D TMDC solar cells are not as efficient as silicon solar cells, they produce more electricity per weight, a property known as “specific power.” This is because a layer that is just 3–5 nanometers thick — or over a thousand times thinner than a human hair — absorbs an amount of sunlight comparable to commercially available solar cells. Their extreme thinness is what earns them the label of “2D” — they are considered “flat” because they are only a few atoms thick.
“High specific power is actually one of the greatest goals of any space-based light harvesting or energy harvesting technology,” says Jariwala. “This is not just important for satellites or space stations but also if you want real utility-scaled solar power in space.”
“The number of solar cells you would have to ship up is so large that no space vehicles currently can take those kinds of materials up there in an economically viable way. So, really the solution is that you double up on lighter weight cells, which give you much more specific power.”
The full potential of 2D TMDC solar cells has not yet been fully realized, so Jariwala and his team have sought to raise the efficiency of the cells even further. Typically, the performance of this type of solar cell is optimized through the fabrication of a series of test devices, but Jariwala’s team believes it is important to do so through modeling it computationally. Additionally, the team thinks that to truly push the limits of efficiency, it is essential to properly account for one of the device’s defining — and challenging to model — features: excitons.
Excitons are produced when the solar cell absorbs sunlight, and their dominant presence is the reason why a 2D TMDC solar cell has such high solar absorption. Electricity is produced by the solar cell when the positively and negatively charged components of an exciton are funneled off to separate electrodes. By modeling the solar cells in this way, the team was able to devise a design with double the efficiency compared to what has already been demonstrated experimentally.
“The unique part about this device is its superlattice structure, which essentially means there are alternating layers of 2D TMDC separated by a spacer or non-semiconductor layer,” says Jariwala. “Spacing out the layers allows you to bounce light many, many times within the cell structure, even when the cell structure is extremely thin.”
“We were not expecting cells that are so thin to see a 12% value. Given that the current efficiencies are less than 5%, my hope is that in the next 4 to 5 years people can actually demonstrate cells that are 10% and upwards in efficiency.”
Jariwala says the next step is to think about how to achieve large, wafer-scale production for the proposed design. “Right now, we are assembling these superlattices by transferring individual materials one on top of the other, like sheets of paper. It’s as if you’re tearing them off from one book, and then pasting them together like a stack of sticky notes,” says Jariwala. “We need a way to grow these materials directly one on top of the other.”
Material Design Strategies for Recovery of Critical Resources from Water
by Omar A. Kazi, Wen Chen, Jamila G. Eatman, Feng Gao, Yining Liu, Yuqin Wang, Zijing Xia, Seth B. Darling in Advanced Materials
For many materials critical to supply chains that will help enable America’s decarbonization transition, resources are limited. Traditional mining is fraught with challenges, so advancing clean energy depends on finding new ways to reliably access critical materials.
Promoting national security and economic competitiveness will require America’s researchers to find new ways to obtain the materials that we need for many technologies. These include batteries, magnets in electric motors, catalysts, nuclear reactors and other essential carbon-free energy technologies. Water represents one underexplored avenue of acquiring these materials. Scientists at the U.S. Department of Energy’s Argonne National Laboratory have recently published a comprehensive review detailing the various mechanisms by which critical materials can be extracted from diverse water streams.
Different types of water offer different kinds of material resources, said Seth Darling, chief science and technology officer for Argonne’s Advanced Energy Technologies directorate.
”The oceans are such a tremendous resource because the total quantities of many valuable and important materials are vast, but they are also highly dilute,” he said. ”Wastewater has also been in need of reframing — we want people to see that wastewater is not truly waste, rather, it’s rich with all sorts of valuable stuff.”
Darling also pointed to groundwater aquifers and geothermal brines as other possible sources of valuable materials. These materials include lithium, which is increasingly in demand for electric vehicle batteries and could be used to help decarbonize our economy.
”Lithium is in the ocean and in geothermal brines; you’d extract it differently from these two sources but it’s important to understand which is cheapest, has the smallest environmental impact, and enables secure supply chains,” Darling said. ”For many other materials, water is underexplored as a source, and that’s something we’re paying increasingly more attention to.”
The technologies that Darling and his colleagues are exploring to extract critical materials from different types of water range from the traditional (like membranes) to the innovative (like interfacial solar steam generators).
Omar Kazi, a Ph.D. student in molecular engineering at the University of Chicago working with Darling, is studying methods to concentrate wastewater streams to recover valuable materials.
”Getting rid of the water through evaporation is an energy-intensive and slow process,” Kazi said. ”In geothermal brines, it can take years for water to evaporate to be able to recover the lithium that’s contained in them, which creates a huge bottleneck. The question we are asking is ’how we can make the water evaporate faster?’”
One way to do that could be through the use of porous photothermal materials, which convert light to heat efficiently. These light absorbers act like a black T-shirt that heats up on a sunny day. That heat is transferred to the water directly at the interface with the surrounding air, significantly accelerating evaporation. Overall, Darling noted, Argonne has rich capabilities in supply chain, life cycle and technoeconomic analyses. In addition, the laboratory specializes in the materials, chemistry and process engineering relevant to critical material extraction. This uniquely positions the lab to help achieve a more secure and circular economy of materials, especially when it comes to getting more out of water streams.
Efficient photon upconversion enabled by strong coupling between silicon quantum dots and anthracene
by Kefu Wang, R. Peyton Cline, Joseph Schwan, Jacob M. Strain, Sean T. Roberts, Lorenzo Mangolini, Joel D. Eaves, Ming Lee Tang in Nature Chemistry
A group of scientists and engineers that includes researchers from The University of Texas at Austin have created a new class of materials that can absorb low energy light and transform it into higher energy light. The new material is composed of ultra-small silicon nanoparticles and organic molecules closely related to ones utilized in OLED TVs. This new composite efficiently moves electrons between its organic and inorganic components, with applications for more efficient solar panels, more accurate medical imaging and better night vision goggles.
“This process gives us a whole new way of designing materials,” said Sean Roberts, an associate professor of chemistry at UT Austin. “It allows us to take two extremely different substances, silicon and organic molecules, and bond them strongly enough to create not just a mixture, but an entirely new hybrid material with properties that are completely distinct from each of the two components.”
Composites are composed of two or more components that adopt unique properties when combined. For example, composites of carbon fibers and resins find use as lightweight materials for airplane wings, racing cars and many sporting products. In the paper co-authored by Roberts, the inorganic and organic components are combined to show unique interaction with light.
Among those properties are the ability to turn long-wavelength photons — the type found in red light, which tends to travel well though tissue, fog and liquids — into short-wavelength blue or ultraviolet photons, which are the type that usually make sensors work or produce a wide range of chemical reactions. This means the material could prove useful in new technologies as diverse as bioimaging, light-based 3D printing and light sensors that can be used to help self-driving cars travel through fog.
“This concept may be able to create systems that can see in near infrared,” Roberts said. “That can be useful for autonomous vehicles, sensors and night vision systems.”
Taking low energy light and making it higher energy also can potentially help to boost the efficiency of solar cells by allowing them to capture near-infrared light that would normally pass through them. When the technology is optimized, capturing low energy light could reduce the size of solar panels by 30%.
Members of the research team, which includes scientists from the University of California Riverside, University of Colorado Boulder and University of Utah, have been working on light conversion of this type for several years. In a previous paper, they described successfully connecting anthracene, an organic molecule that can emit blue light, with silicon, a material used in solar panels and in many semiconductors. Seeking to amplify the interaction between these materials, the team developed a new method for forging electrically conductive bridges between anthracene and silicon nanocrystals. The resulting strong chemical bond increases the speed with which the two molecules can exchange energy, almost doubling the efficiency in converting lower energy light to higher energy light, compared with the team’s previous breakthrough.
Evaluation of alternative power-to-chemical pathways for renewable energy exports
by Muhammad Aadil Rasool, Kaveh Khalilpour, Ahmad Rafiee, Iftekhar Karimi, Reinhard Madlener in Energy Conversion and Management
A team of researchers has created a new supply chain model which could empower the international hydrogen renewable energy industry.
Hydrogen has been touted as the clean fuel of the future; it can be generated from water and produces zero carbon emissions. However, it is currently expensive to transport over long distances, and currently no infrastructure is in place to do so.
The new supply chain model, created by researchers in Australia, Singapore and Germany, successfully guides the development of international transport of hydrogen and its embodied energy. Associate Professor Kaveh Khalilpour, from the University of Technology Sydney (UTS) and lead of the report, said supply chain design is critical for making hydrogen economic.
“We looked at the renewable hydrogen export from Australia to Singapore, Japan, and Germany. Surprisingly, the analysis revealed that it matters whether the goal is to export ‘hydrogen the atom’ or ‘hydrogen the energy’. Each choice leads to a different supply chain system.
“Therefore, a thorough understanding of the whole system is necessary for correct decision making,” said Associate Professor Khalilpour.
“The abundance of renewable energy resources in Australia, as well as its stable economy, means the country can attract investments in building these green value chains in our region and even as far away as Europe.”
Hydrogen is expected to help diversify Australia’s renewable energy resource beyond solar and wind power. This is seen as critical to the country’s energy security, as well as necessary for climate change mitigation. Hydrogen is just an energy carrier, i.e. not a primary energy source, and thus only a means to an end for transporting renewable energy from one place to another.
“The key business question around the emerging hydrogen economy is whether commodities such as green hydrogen, methanol or ammonia can be exported profitably and competitively also over long distances and across the oceans, thus bringing green energy to other places in the world. “If this is so, this will also have major international energy and climate policy implications,” said Professor Reinhard Madlener, co-lead of the project, from RWTH Aachen University, Germany.
“Our model suggests that methanol shows great promise as a chemical carrier for exporting renewable energy from Australia at low costs,” said Professor Iftekhar Karimi, from the National University of Singapore, and co-lead of the project.
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