GT/ Harnessing low-grade heat for energy conversion
Energy & green technology biweekly vol.57, 13th September — 28th September
TL;DR
- A research team has achieved significant breakthroughs in harnessing low-grade heat sources (<100 °C) for efficient energy conversion.
- Scientists and industry leaders worldwide are looking for answers on how to make aviation sustainable by 2050 and choosing a viable sustainable fuel is a major sticking point. Aerospace engineers took a full inventory of the options to make a data-driven assessment about how they stack up in comparison.
- A scientific breakthrough brings mass production of the next generation of cheaper and lighter perovskite solar cells one step closer.
- Researchers have genetically engineered a marine microorganism to break down plastic in salt water. Specifically, the modified organism can break down polyethylene terephthalate (PET), a plastic used in everything from water bottles to clothing that is a significant contributor to microplastic pollution in oceans.
- A chemist envisions a future where every house is powered by renewable energy stored in batteries. He has created a new battery that could have profound implications for the large-scale energy storage needed by wind and solar farms.
- The output of wind turbines can rise or fall by 50 per cent in a matter of seconds. Such fluctuations in the megawatt range put a strain on both power grids and the turbines themselves. A new study presents a new stochastic method that could help to mitigate these sudden swings and achieve a more consistent electricity production.
- Researchers discover excellent thermoelectric properties of nickel-gold alloys. These can be used to efficiently convert heat into electrical energy.
- Scientists have found a way to harvest hydrogen from plastic waste using a low-emissions method that generates graphene as a by-product, which could help offset production costs.
- A research team has achieved a significant breakthrough in the development of a hybrid silicon photocatalyst.
- Achieving photochemical upconversion in a solid state is a step closer to reality, thanks to a new technique that could unlock vital innovations in renewable energy, water purification and advanced healthcare.
- 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
Enhancing Efficiency of Low‐Grade Heat Harvesting by Structural Vibration Entropy in Thermally Regenerative Electrochemical Cycles
by Ahreum Choi, You‐Yeob Song, Juyoung Kim, Donghyeon Kim, Min‐Ho Kim, Seok Woo Lee, Dong‐Hwa Seo, Hyun‐Wook Lee in Advanced Materials
A team of researchers, jointly led by Professor Hyun-Wook Lee and Professor Dong-Hwa Seo from the School of Energy and Chemical Engineering at the Ulsan National Institute of Science and Technology (UNIST), in collaboration with Professor Seok Woo Lee from Nanyang Technological University in Singapore, has achieved significant breakthroughs in harnessing low-grade heat sources (<100 °C) for efficient energy conversion. Their groundbreaking work focuses on developing a highly efficient Thermally Regenerative Electrochemical Cycle (TREC) system capable of converting small temperature differences into usable energy.
Conventional energy-harvesting systems face challenges when it comes to effectively utilizing low-grade heat sources. However, TREC systems offer an attractive solution as they integrate battery functionality with thermal-energy-harvesting capabilities. In this study, the research team delved into the role of structural vibration modes to enhance the efficacy of TREC systems.
By analyzing how changes in covalent bonding influence vibration modes — specifically affecting structural water molecules — the researchers discovered that even minute amounts of water induce strong structural vibrations within cyanide ligands’ A1g stretching mode. These vibrations substantially contribute to a larger temperature coefficient (ɑ) within a TREC system. Based on these insights, the team designed and implemented a highly efficient TREC system using a sodium-ion-based aqueous electrolyte.
“This study provides valuable insights into how structural vibration modes can enhance the energy-harvesting capabilities of TREC systems,” explained Professor Hyun-Wook Lee. “Our findings deepen our understanding of Prussian Blue analogs’ intrinsic properties regulated by these vibration modes — opening up new possibilities for improved energy conversion.”
The potential applications for TREC systems are vast, particularly in wearable technologies and other devices where small temperature differentials exist. By effectively capturing and converting low-grade heat into usable energy, TREC systems offer a promising pathway towards the development of next-generation secondary batteries.
Review of sustainable energy carriers for aviation: Benefits, challenges, and future viability
by Phillip J. Ansell in Progress in Aerospace Sciences
Scientists and industry leaders worldwide are looking for answers on how to make aviation sustainable by 2050 and choosing a viable sustainable fuel is a major sticking point. Phil Ansell, aerospace engineer at the University of Illinois Urbana-Champaign, took a full inventory of the options to make a data-driven assessment about how they stack up in comparison. He reviewed over 300 research projects from across different sectors, not just aerospace, to synthesize the ideas and draw conclusions to help direct the dialogue about sustainable aviation toward a permanent solution.
Ansell said several key energy carriers emerged, including bio jet fuel pathways for synthetic kerosene, power-to-liquid pathways for synthetic kerosene, liquid hydrogen, ammonia, liquid natural gas, ethanol, methanol, and battery electric systems. Ansell compared each of them to conventional fossil-derived aviation turbine fuel. For each of the alternate fuels Ansell addressed factors such as how their material properties impact aircraft performance and fuel handling, emissions, cost and scalability, and resource and land requirements, as well as social impacts, which can be difficult to measure.
“Let’s face it, if we want to do this at scale, we need all three pillars of the environmental, economic, and societal contributions, to make that energy carrier sustainable, and every stakeholder in the value chain sees the challenges differently,” Ansell said. “Because the production and infrastructure costs required to adopt an alternative fuel source are significant, people think we can only pick one, the biggest contenders being bio jet fuel and hydrogen,” Ansell said. “But the choice doesn’t have to be mutually exclusive. For example, we can use hydrogen to produce synthetic aviation fuels like the power-to-liquid pathway or use biomass to produce hydrogen.”
Ansell admitted this is not what he typically studies, but his research and teaching areas in aircraft design and aerodynamics must consider where the energy will come from to make flight possible. So, for any fuel associated with a bio aspect Ansell had to look at the stresses it might create for crops.
“I leaned on a lot of the observations from the community, especially for the land use change question,” he said. “It is so driven case by case. Making a broad assessment doesn’t do it justice, because land use changes depend on their location.”
Ansell said he has been working with hydrogen for several years and battery/electric systems before that, so he needed to remain objective and all the data to drive the conclusion.
“About eight years ago, I realized that battery systems are a pie-in-the-sky solution. The technology challenge is insurmountable. The weight and volume required for batteries is too difficult to close. I think my biases were from the fact that I’ve been studying hydrogen for a long time, and I think it has real potential. That’s one of the conclusions I arrived at from the data, and I think I would have learned that independently.”
Ansell said hydrogen presents infrastructural and integration challenges, unique to the aircraft platform and unique to the cryogenic handling of fuel on aircraft.
“The technological challenges of hydrogen are very solvable. And I can say that with confidence because we’ve done it as a society.” He referred to Tupolev 155, a commercial scale aircraft which was flown by the former Soviet Union with liquid hydrogen in the 1980s on a relevant airframe. Even earlier experimental studies were conducted by NASA. “It will take a bit longer to implement at scale, but it’s doable.”
In the study, Ansell examined numerous options to produce biofuel from just about anything, from municipal waste to seaweed and algae.
“Basically, anything that you can burn, create energy from, decompose, can be turned into a jet fuel. We’ve already been using corn to produce ethanol. But if you were to take corn, ferment it, then turn that ethanol into jet fuel, you now have lost the ability to feed people or animals that corn. This is one of the challenges of all first-generation biofuels.”
He said people are trying to use the stover, the parts of a corn plant left on the ground after harvesting to make fuel. Corn stover is full of sugar but it’s difficult to extract.
Modification of Hydrophobic Self‐Assembled Monolayers with Nanoparticles for Improved Wettability and Enhanced Carrier Lifetimes Over Large Areas in Perovskite Solar Cells
by W. Hashini K. Perera, Mateus G. Masteghin, Hongjae Shim, Joshua D. Davies, Joshua L. Ryan, Steven J. Hinder, Jae S. Yun, Wei Zhang, K. D. G. Imalka Jayawardena, S. Ravi P. Silva in olar RRL
A scientific breakthrough brings mass production of the next generation of cheaper and lighter perovskite solar cells one step closer thanks to researchers at the University of Surrey’s Advanced Technology Institute (ATI).
A nanoscale ‘ink’ coating of aluminium oxide on metal halide perovskite improves the potential of this emerging photovoltaic technology and stabilises the drop in energy output which currently plagues perovskite technology.
Hashini Perera, lead author of the study at the University of Surrey said: “In the past, metal oxides have been shown to either benefit or degrade the performance of perovskite solar cells. We’ve identified aluminium oxide which can improve performance and minimises the drop in efficiency during conditioning of perovskite solar cells. We show that this nano-oxide allows a uniform coating of perovskite material on highly promising organic molecules that self-assemble on a surface and improve device output.”
Dr Imalka Jayawardena, from the University of Surrey’s Advanced Technology Institute said: “Performance limits of traditional solar cells are why researchers are switching to examining perovskite as the next-generation solar technology, especially as applications both terrestrial and in space are rapidly growing. Our key development in solar panel technology shows a cost-effective approach to scaling of perovskite solar cells, a development which could help countries around the world to reach their net zero targets faster.”
Prof. Ravi Silva, corresponding author from the ATI, University of Surrey said: “Solar and wind energy costs are rapidly decreasing based on technology improvements, to the level where worldwide over 80% of all new additional power generation capacity is based on renewables. The levelised cost of solar electricity is now cheaper than most other power generating sources. With the maturing of perovskite solar modules, the levelised cost of electricity will significantly decrease further, and that is why this is such an exciting area to work.”
Breakdown of polyethylene therepthalate microplastics under saltwater conditions using engineered Vibrio natriegens
by Tianyu Li, Stefano Menegatti, Nathan Crook in AIChE Journal
Researchers have genetically engineered a marine microorganism to break down plastic in salt water. Specifically, the modified organism can break down polyethylene terephthalate (PET), a plastic used in everything from water bottles to clothing that is a significant contributor to microplastic pollution in oceans.
“This is exciting because we need to address plastic pollution in marine environments,” says Nathan Crook, corresponding author of a paper on the work and an assistant professor of chemical and biomolecular engineering at North Carolina State University.
“One option is to pull the plastic out of the water and put it in a landfill, but that poses challenges of its own. It would be better if we could break these plastics down into products that can be re-used. For that to work, you need an inexpensive way to break the plastic down. Our work here is a big step in that direction.”
To address this challenge, the researchers worked with two species of bacteria. The first bacterium, Vibrio natriegens, thrives in saltwater and is remarkable — in part — because it reproduces very quickly. The second bacterium, Ideonella sakaiensis, is remarkable because it produces enzymes that allow it to break down PET and eat it.
The researchers took the DNA from I. sakaiensis that is responsible for producing the enzymes that break down plastic, and incorporated that genetic sequence into a plasmid. Plasmids are genetic sequences that can replicate in a cell, independent of the cell’s own chromosome. In other words, you can sneak a plasmid into a foreign cell, and that cell will carry out the instructions in the plasmid’s DNA. And that’s exactly what the researchers did here. By introducing the plasmid containing the I. sakaiensis genes into V. natriegens bacteria, the researchers were able to get V. natriegens to produce the desired enzymes on the surface of their cells. The researchers then demonstrated that V. natriegens was able to break down PET in a saltwater environment at room temperature.
“This is scientifically exciting because this is the first time anyone has reported successfully getting V. natriegens to express foreign enzymes on the surface of its cells,” Crook says.
“From a practical standpoint, this is also the first genetically engineered organism that we know of that is capable of breaking down PET microplastics in saltwater,” says Tianyu Li, first author of the paper and a Ph.D. student at NC State. “That’s important, because it is not economically feasible to remove plastics from the ocean and rinse high concentration salts off before beginning any processes related to breaking the plastic down.”
“However, while this is an important first step, there are still three significant hurdles,” Crook says. “First, we’d like to incorporate the DNA from I. sakaiensis directly into the genome of V. natriegens, which would make the production of plastic-degrading enzymes a more stable feature of the modified organisms. Second, we need to further modify V. natriegens so that it is capable of feeding on the byproducts it produces when it breaks down the PET. Lastly, we need to modify the V. natriegens to produce a desirable end product from the PET — such as a molecule that is a useful feedstock for the chemical industry.
“Honestly, that third challenge is the easiest of the three,” says Crook. “Breaking down the PET in saltwater was the most challenging part.
Development of high-voltage and high-energy membrane-free nonaqueous lithium-based organic redox flow batteries
by Rajeev K. Gautam, Xiao Wang, Amir Lashgari, Soumalya Sinha, Jack McGrath, Rabin Siwakoti, Jianbing “Jimmy” Jiang in Nature Communications
Jimmy Jiang envisions a future where every house is powered by renewable energy stored in batteries. In his chemistry lab, Jiang and his students at the University of Cincinnati have created a new battery that could have profound implications for the large-scale energy storage needed by wind and solar farms.
Innovations such as UC’s will have profound effects on green energy, Jiang said. Batteries store renewable energy for when it’s needed, not just when it’s produced. This is crucial for getting the most out of wind and solar power, he said.
“Energy generation and energy consumption is always mismatched,” he said. “That’s why it’s important to have a device that can store that energy temporarily and release it when it’s needed.”
Traditional car batteries contain a mix of sulfuric acid and water. And while they are inexpensive and made from readily available materials, they have severe drawbacks for industrial or large-scale use. They have a very low energy density, which isn’t useful for storing megawatts of power needed to power a city. And they have a low threshold for electrochemical stability. Jiang said that means they can blow up.
“Water has a voltage limit. Once the voltage of an aqueous battery exceeds the stability window of 1.5 volts, the water can decompose or be split into hydrogen and oxygen, which is explosive,” he said.
But Jiang and his students have developed a battery without water that can generate nearly 4 volts of power. Jiang’s novel design does so without a membrane-separator, which are among the priciest parts of these kinds of batteries, he said.
“Membranes are super expensive,” Jiang said. “We developed a new type of energy storage material that improves performance at a lower cost.” Likewise, membranes are inefficient, he said. “They can’t separate the positive and negative sides completely, so there is always crossover,” he said.
The group has submitted provisional patent applications, he said.
“There is still a long way to go,” Jiang said. But he said we are hurtling toward a battery revolution in the next 20 years. “I am confident about that. There is a lot of intense research going into pushing the boundaries of battery performance,” he said.
His students are equally enthusiastic. Doctoral student and study co-author Rabin Siwakoti said the battery offers higher energy density.
“So even a small battery can give you more energy,” he said. “We’ve managed to eliminate the membrane in a battery, which is a huge component of upfront costs. It’s as much as 30% of the cost of the battery,” co-author and doctoral student Jack McGrath said.
Discontinuous Jump Behavior of the Energy Conversion in Wind Energy Systems
by Pyei Phyo Lin, Matthias Wächter, M. Reza Rahimi Tabar, Joachim Peinke in PRX Energy
The power output of wind turbines can go up or down by 50 percent within seconds. Such fluctuations in the megawatt range put a strain on both power grids and the turbines themselves. A new study by researchers from the University of Oldenburg in Germany and the Sharif University of Technology in Tehran (Iran) presents a method that could help to prevent these power swings.
According to the study, it is the control systems of wind turbines that are mainly responsible for short-term fluctuations in electrical output. The research results also point to how these systems can be optimised to ensure that the turbines’ energy output is more consistent.
The research team led by lead author Dr Pyei Phyo Lin from the University of Oldenburg analysed data from several turbines in a wind farm. “Because wind turbines operate under turbulent wind conditions — similar to a plane landing in strong winds — all the measured data display multiple fluctuations and no clear signal can be detected. We refer to this as ‘noise’,” Lin explained. The physics engineer and his colleagues applied stochastic methods to analyse time series of the wind speed, the electrical output of the turbines and the rotational speed of the generator.
Using this innovative mathematical approach, they were able to disentangle the noise in the data and separate it into two different components, one of which one is caused by the wind while the other results from the reactions of the turbine’s control system.
“Noise is often considered an unpleasant effect that interferes with measurements,” said Lin. “Now the noise provides us with new information about the system — that’s a new quality,” added co-author Dr Matthias Wächter, who heads the Stochastic Analysis research group at the University of Oldenburg.
As the team explains, the results of its study indicate that the reactions of wind turbine control systems to abrupt wind fluctuations are often suboptimal: these systems tend to switch control strategies, which can lead to the observed strong fluctuations in electrical output. The new findings pave the way for turbulent wind phenomena to be decoupled from the control systems’ reactions: “In this way, it will be possible to refine the control systems to ensure that wind turbines generate power more consistently,” said turbulence expert Professor Dr Joachim Peinke from the University of Oldenburg, who was also involved in the study. This would also boost the efficiency of wind turbines and extend their lifespans, he added.
High thermoelectric performance in metallic NiAu alloys via interband scattering
by Fabian Garmroudi, Michael Parzer, Alexander Riss, Cédric Bourgès, Sergii Khmelevskyi, Takao Mori, Ernst Bauer, Andrej Pustogow in Science Advances
Thermoelectrics enable the direct conversion of heat into electrical energy — and vice versa. This makes them interesting for a range of technological applications. In the search for thermoelectric materials with the best possible properties, a research team at TU Wien investigated various metallic alloys. A mixture of nickel and gold proved particularly promising.
Using thermoelectrics to generate electricity is nothing new. Since the middle of the 20th century, they have been used to generate electrical energy in space exploration, but thermoelectrics are also used in everyday applications such as portable refrigerators. Moreover, they could also be used in industrial environments to convert waste heat into green electricity, to name just one of the potential applications.
The thermoelectric effect is based on the movement of charged particles that migrate from the hotter to the colder side of a material. This results in an electrical voltage — the so-called thermoelectric voltage — which counteracts the thermally excited movement of the charge carriers. The ratio of the built-up thermoelectric voltage and the temperature difference defines the Seebeck coefficient, named after the German physicist Thomas Johann Seebeck, which is an important parameter for the thermoelectric performance of a material. The important requirement here is that there is an imbalance between positive and negative charges, as they compensate each other.
“Although Seebeck discovered the thermoelectric effect in common metals more than 200 years ago, nowadays metals are hardly considered as thermoelectric materials because they usually have a very low Seebeck coefficient,” explains Fabian Garmroudi, first author of the study. On the one hand, metals such as copper, silver or gold have extremely high electrical conductivity; on the other hand, their Seebeck coefficient is vanishingly small in most cases.
Physicists from the Institute of Solid State Physics (TU Wien) have now succeeded in finding metallic alloys with high conductivity and an exceptionally large Seebeck coefficient. Mixing the magnetic metal nickel with the noble metal gold radically changes the electronic properties. As soon as the yellowish colour of gold disappears when about 10 % nickel is added, the thermoelectric performance increases rapidly. The physical origin for the enhanced Seebeck effect is rooted in the energy-dependent scattering behavior of the electrons — an effect fundamentally different from semiconducting thermoelectrics. Due to the particular electronic properties of the nickel atoms, positive charges are scattered more strongly than negative charges, resulting in the desired imbalance and hence a high thermoelectric voltage.
“Imagine a race between two runners, where one person runs on a free track, but the other person has to get through many obstacles. Of course, the person on the free track advances faster than the opponent, who has to slow down and change direction much more often,” compares Andrej Pustogow, senior author of the study, the flow of electrons in metallic thermoelectrics. In the alloys studied here, the positive charges are strongly scattered by the nickel electrons, while the negative charges can move practically undisturbed.
The combination of extremely high electrical conductivity and simultaneously a high Seebeck coefficient leads to record thermoelectric power factor values in nickel-gold alloys, which exceed those of conventional semiconductors by far.
“With the same geometry and fixed temperature gradient, many times more electrical power could be generated than in any other known material,” explains Fabian Garmroudi. In addition, the high power density may enable everyday applications in the large-scale sector in the future. “Already with the current performance, smartwatches, for instance, could already be charged autonomously using the wearer’s body heat,” Andrej Pustogow gives as an example.
“Even though gold is an expensive element, our work represents a proof of concept. We were able to show that not only semiconductors, but also metals can exhibit good thermoelectric properties that make them relevant for diverse applications. Metallic alloys have various advantages over semiconductors, especially in the manufacturing process of a thermoelectric generator,” explains Michael Parzer, one of the lead authors of the study.
The fact that the researchers were able to experimentally show that nickel-gold alloys are extremely good thermoelectrics is no coincidence. “Even before starting our experimental work, we calculated with theoretical models which alloys were most suitable,” reveals Michael Parzer. Currently, the group is also investigating other promising candidates that do not require the expensive element gold.
Synthesis of Clean Hydrogen Gas from Waste Plastic at Zero Net Cost
by Kevin M. Wyss, Karla J. Silva, Ksenia V. Bets, Wala A. Algozeeb, Carter Kittrell, Carolyn H. Teng, Chi Hun Choi, Weiyin Chen, Jacob L. Beckham, Boris I. Yakobson, James M. Tour in Advanced Materials
Hydrogen is viewed as a promising alternative to fossil fuel, but the methods used to make it either generate too much carbon dioxide or are too expensive. Rice University researchers have found a way to harvest hydrogen from plastic waste using a low-emissions method that could more than pay for itself.
“In this work, we converted waste plastics — including mixed waste plastics that don’t have to be sorted by type or washed — into high-yield hydrogen gas and high-value graphene,” said Kevin Wyss, a Rice doctoral alumnus and lead author on a study. “If the produced graphene is sold at only 5% of current market value — a 95% off sale! — clean hydrogen could be produced for free.”
By comparison, ‘green’ hydrogen — produced using renewable energy sources to split water into its two component elements — costs roughly $5 for just over two pounds. Though cheaper, most of the nearly 100 million tons of hydrogen used globally in 2022 was derived from fossil fuels, its production generating roughly 12 tons of carbon dioxide per ton of hydrogen.
“The main form of hydrogen used today is ‘gray’ hydrogen, which is produced through steam-methane reforming, a method that generates a lot of carbon dioxide” said James Tour, Rice’s T. T. and W. F. Chao Professor of Chemistry and a professor of materials science and nanoengineering. “Demand for hydrogen will likely skyrocket over the next few decades, so we can’t keep making it the same way we have up until now if we’re serious about reaching net zero emissions by 2050.”
The researchers exposed plastic waste samples to rapid flash Joule heating for about four seconds, bringing their temperature up to 3100 degrees Kelvin. The process vaporizes the hydrogen present in plastics, leaving behind graphene — an extremely light, durable material made up of a single layer of carbon atoms.
“When we first discovered flash Joule heating and applied it to upcycle waste plastic into graphene, we observed a lot of volatile gases being produced and shooting out of the reactor,” Wyss said. “We wondered what they were, suspecting a mix of small hydrocarbons and hydrogen, but lacked the instrumentation to study their exact composition.”
Using funding from the United States Army Corps of Engineers, the Tour lab acquired the necessary equipment to characterize the vaporized contents.
“We know that polyethylene, for example, is made of 86% carbon and 14% hydrogen, and we demonstrated that we are able to recover up to 68% of that atomic hydrogen as gas with a 94% purity,” Wyss said. “Developing the methods and expertise to characterize and quantify all the gases, including hydrogen, produced by this method was a difficult but rewarding process for me.
“I am glad that techniques I learned and used in this work — specifically life-cycle assessment and gas chromatography — can be applied to other projects in our group. I hope that this work will allow for the production of clean hydrogen from waste plastics, possibly solving major environmental problems like plastic pollution and the greenhouse gas-intensive production of hydrogen by steam methane reforming.”
Solar Biomass Reforming and Hydrogen Production with Earth‐Abundant Si‐Based Photocatalysts
by Yuri Choi, Sungho Choi, Inhui Lee, Trang Vu Thien Nguyen, Sanghyun Bae, Yong Hwan Kim, Jaegeon Ryu, Soojin Park, Jungki Ryu in Advanced Materials
A team of researchers, led by Professor Jungki Ryu in the School of Energy and Chemical Engineering at UNIST and Professor Soojin Park from Pohang University of Science and Technology (POSTECH), have achieved a significant breakthrough in the development of a hybrid silicon photocatalyst. This innovative catalyst utilizes solar power to produce hydrogen and high-value compounds efficiently, marking a major step forward in green hydrogen production technology.
The newly developed photocatalyst is both non-toxic and eco-friendly, addressing the limitations associated with previous catalysts that were not sunlight-responsive or posed toxicity concerns. Silicon-based photocatalysts demonstrate excellent light absorption properties, making them highly efficient in utilizing solar energy. Moreover, these non-toxic materials do not emit harmful chemicals during their production process.
Previous research faced challenges in achieving continuous production of hydrogen alongside high-value compounds due to a lack of suitable catalysts. Toxic catalysts used under strong base conditions often led to environmental pollution issues. Additionally, as oxide layers formed on traditional silicon photocatalysts during reactions, it negatively impacted hydrogen production efficiency over time.
To overcome these obstacles, the research team developed a hybrid silicon photocatalyst by uniformly coating nickel-doped graphene quantum dots onto the surface of 2 to 3 nm thick silicon flakes. The modified surface enabled significantly higher hydrogen production efficiency compared to conventional silicon photocatalysts — achieving an impressive rate of 14.2 mmol gcat−1 h−1 — a substantial improvement equating to approximately 28 times higher performance.
Furthermore, through oxidation reactions using biomass instead of water — an organic substance derived from biological sources — the hybrid silicon photocatalyst demonstrated its capability for producing high-value compounds alongside hydrogen production. The catalyst also maintained 98% of its original form, ensuring long-term stability.
Professor Ryu stated, “Previous research on hydrogen production has been limited to photocatalysts that absorb ultraviolet rays or involve toxic catalysts. Our non-toxic and cost-effective silicon photocatalyst is a significant advancement as it enables high-efficiency hydrogen production through superior solar absorption.”
Professor Park added, “The surface modification technique utilizing nickel-doped graphene quantum dots can be applied not only to silicon photocatalysts but also to various other types of photocatalysts, opening up new possibilities in energy applications.”
Nanoporous Solid-State Sensitization of Triplet Fusion Upconversion
by Thilini Ishwara, Jiale Feng, Damon M. de Clercq, Rugang Geng, Jessica Alves, Dane R. McCamey, Michael. P. Nielsen, Timothy W. Schmidt in ACS Energy Letters
Achieving photochemical upconversion in a solid state is a step closer to reality, thanks to a new technique that could unlock vital innovations in renewable energy, water purification and advanced healthcare.
Exciton Science researchers based at UNSW Sydney have demonstrated that a key stage in the upconversion process can be achieved in the solid state, making it more likely that a functioning device can be manufactured at commercial scale. Possible applications include hydrogen catalysis and solar energy generation. Their work is likely to drive major changes in the approach of scientists around the world researching this challenging but potentially transformational field.
Professor Tim Schmidt of UNSW Sydney, an Exciton Science Chief Investigator and the senior author on the paper, said: “I think people are going to immediately start copying us. I consider this a breakthrough because this approach can be adapted to upconverting into the ultraviolet or from the infrared. There’s so much we can do with it.”
Upconversion involves gluing two low-energy photons of light together to create more energetic, visible light, which can be captured by solar cells or harnessed for other purposes. The technical term for the gluing process is ‘triplet-triplet annihilation’, which produces a ‘singlet exciton’. An exciton is a quasiparticle which exists when an electron and the hole it is bound to becomes excited by light or another source of energy. Controlled and reliable triplet-triplet annihilation and the photochemical upconversion it enables could raise the efficiency limit of solar energy devices from 33.7% to 40% or beyond. Much of the fundamental research on upconversion is performed with liquid samples. For the mechanism to be useful in real-world devices applications, it must be effectively demonstrated in a solid state.
In this work, Exciton Science Research Fellow Dr Thilini Ishwara and her colleagues created a thin film of nanostructured alumina stained with a sensitizer. The pores of the structure are filled with emitter molecules in concentrated solution, which allows a highly promising photon generation quantum yield of 9.4%. The next step for the researchers is to move beyond the concentrated solution used in this approach and to achieve similar results in an entirely solid state, potentially by using a gel-like substance.
“If you can make it small enough, you could use it for even doing chemistry in the body,” Thilini said. “You can generate higher energy light at a targeted place inside the body to treat tumors or create medicines with laser precision.
“Water purification is another use for upconversion. If you can upconvert the visible spectrum into quite a harsh UV, you can kill bugs and save millions of lives each year in the developing world.”
Other applications potentially able to be powered by new upconversion techniques include infrared technology like night vision, and even 3D printing.
MISC
Subscribe to Paradigm!
Medium. Twitter. Telegram. Telegram Chat. Reddit. LinkedIn.
Main Sources
Research articles
