TL;DR

• Chemical engineers have invented a solar-powered artificial leaf, built on a novel electrode which is transparent and porous, capable of harvesting water from the air for conversion into hydrogen fuel. The semiconductor-based technology is scalable and easy to prepare.
• A new kind of solar panel has achieved 9% efficiency in converting water into hydrogen and oxygen — mimicking a crucial step in natural photosynthesis. Outdoors, it represents a major leap in the technology, nearly 10 times more efficient than solar water-splitting experiments of its kind.
• Researchers have developed a system that can transform plastic waste and greenhouse gases into sustainable fuels and other valuable products — using just the energy from the Sun.
• A new model quantifies emissions that will be generated by computers on fully autonomous vehicles. If self-driving cars are widely adopted, their emissions will rival those generated by all the data centers in the world today. Keeping emissions at or below those levels would require hardware efficiency to improve more rapidly than its current pace.
• The conversion of solar energy into hydrogen energy represents a promising and green technique for addressing the energy shortage and reducing fossil fuel emissions. A research team recently developed a lead-free perovskite photocatalyst that delivers highly efficient solar energy-to-hydrogen conversion.
• Synthesizing ammonia, the key ingredient in fertilizer, is energy intensive and a significant contributor to greenhouse gas warming of the planet. Chemists designed and synthesized porous materials — metal-organic frameworks, or MOFs — that bind and release ammonia at more moderate pressures and temperatures than the standard Haber-Bosch process for making ammonia. The MOF doesn’t bind to any of the reactants, making capture and release of ammonia less energy intensive and greener.
• A novel technique called Underground Gravity Energy Storage turns decommissioned mines into long-term energy storage solutions, thereby supporting the sustainable energy transition.
• The existing flow battery technologies cost more than $200/kilowatt hour and are too expensive for practical application, but engineers have now developed a more compact flow battery cell configuration that reduces the size of the cell by 75%, and correspondingly reduces the size and cost of the entire flow battery. The work could revolutionize how everything from major commercial buildings to residential homes are powered.
• Environmental scientists calculate that about two percent of visibly floating plastic may disappears from the ocean surface by UV light from the sun each year.
• Chemical and environmental engineers detailed a method to convert plastic waste into a highly porous form of charcoal that has a whopping surface area of about 400 square meters per gram of mass. It could potentially be added to soil to improve water retention and aeration of farmlands.
• 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

Transparent Porous Conductive Substrates for Gas‐Phase Photoelectrochemical Hydrogen Production

by Marina Caretti, Elizaveta Mensi, Raluca‐Ana Kessler, Linda Lazouni, Benjamin Goldman, Loï Carbone, Simon Nussbaum, Rebekah A. Wells, Hannah Johnson, Emeline Rideau, Jun‐ho Yum, Kevin Sivula in Advanced Materials

A device that can harvest water from the air and provide hydrogen fuel — entirely powered by solar energy — has been a dream for researchers for decades. Now, EPFL chemical engineer Kevin Sivula and his team have made a significant step towards bringing this vision closer to reality. They have developed an ingenious yet simple system that combines semiconductor-based technology with novel electrodes that have two key characteristics: they are porous, to maximize contact with water in the air; and transparent, to maximize sunlight exposure of the semiconductor coating. When the device is simply exposed to sunlight, it takes water from the air and produces hydrogen gas.

What’s new? It’s their novel gas diffusion electrodes, which are transparent, porous and conductive, enabling this solar-powered technology for turning water — in its gas state from the air — into hydrogen fuel.

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

Photographs of the a) fused SiO2 fiber felt (TPS) and b) the FTO-coated TPCS qualitatively show the substrate transparency. Scanning electron micrographs show c) top-down and d) cross-sectional morphology. Note that the FTO coating appears as a lighter shade than the SiO2. e) UV–vis total transmittance (red curves) and total reflectance (blue curves) of the TPS (solid lines) and TPCS (dashed lines). f) Typical stress-strain curves from the biaxial flexure test on a TPS and a TPCS. All data correspond to substrates with a SiO2 fiber loading of 4 mg cm−2 (10 min FTO deposition for TPCS).

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

The transparent gas diffusion electrodes developed by Sivula and his team, when coated with a light harvesting semiconductor material, indeed act like an artificial leaf, harvesting water from the air and sunlight to produce hydrogen gas. The sunlight’s energy is stored in the form of hydrogen bonds. Instead of building electrodes with traditional layers that are opaque to sunlight, their substrate is actually a 3-dimensional mesh of felted glass fibers.

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

Scanning electron micrographs (a–e) of the TPCS coated with various semiconductors: (a,b) show coating with CuSCN via electrodeposition, (c) shows a Cu2O/TPCS cross-section (electro-converted from CuSCN), and (d,e) show the BHJ coating on the CuSCN/TPCS prepared by dip coating. The inset photographs in (a, c, e) show optical images of the coated TPCSs. f) linear-scanning voltammetry of a TPCS/CuSCN/BHJ PBDTTTPD:P(NDI2HD-T) (1.5:1 w:w) photocathode in sacrificial aqueous electrolyte (1.2 m Eu(NO3)3, pH 2) under intermittent 1-sun simulated solar illumination.

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

Sivula wanted to show that the PEC technology can be adapted for harvesting humidity from the air instead, leading to the development of their new gas diffusion electrode. Electrochemical cells (e.g. fuel cells) have already been shown to work with gases instead of liquids, but the gas diffusion electrodes used previously are opaque and incompatible with the solar-powered PEC technology. Now, the researchers are focusing their efforts into optimizing the system. What is the ideal fiber size? The ideal pore size? The ideal semiconductors and membrane materials? These are questions that are being pursued in the EU Project “Sun-to-X,” which is dedicated to advance this technology, and develop new ways to convert hydrogen into liquid fuels.

Photograph of the expanded view a) and cross-sectional schematic b) of the gas-phase half-cell employed in this work. c) initial LSV of a PEM/Pt/(PTB7-Th:PC61BM) /CuSCN/TPCS photoelectrode membrane assembly under intermittent simulated 1-sun illumination. d) CA of the photocathode membrane assembly from (c) at 0 V versus RHE for a 5 min time scale under continuous 1-sun illumination. e) 1 h CA of the photocathode membrane assembly at 0 V versus RHE with simultaneous H2 gas measurements.

In order to make transparent gas diffusion electrodes, the researchers start with a type of glass wool, which is essentially quartz (also known as silicon oxide) fibers and process it into felt wafers by fusing the fibers together at high temperature. Next, the wafer is coated with a transparent thin film of fluorine-doped tin oxide, known for its excellent conductivity, robustness and ease to scale-up. These first steps result in a transparent, porous, and conducting wafer, essential for maximizing contact with the water molecules in the air and letting photons through. The wafer is then coated again, this time with a thin-film of sunlight-absorbing semiconductor materials. This second thin coating still lets light through, but appears opaque due to the large surface area of the porous substrate. As is, this coated wafer can already produce hydrogen fuel once exposed to sunlight.

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

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

Solar-to-hydrogen efficiency of more than 9% in photocatalytic water splitting

by Peng Zhou, Ishtiaque Ahmed Navid, Yongjin Ma, Yixin Xiao, Ping Wang, Zhengwei Ye, Baowen Zhou, Kai Sun, Zetian Mi in Nature

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

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

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

Temperature-controllable photocatalytic OWS system and reaction condition optimization.

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

The outstanding result comes from two advances. The first is the ability to concentrate the sunlight without destroying the semiconductor that harnesses the light.

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

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

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

For the outdoor experiment, Zhou set up a lens about the size of a house window to focus sunlight onto an experimental panel just a few inches across. Within that panel, the semiconductor catalyst was covered in a layer of water, bubbling with the hydrogen and oxygen gasses it separated. The catalyst is made of indium gallium nitride nanostructures, grown onto a silicon surface. That semiconductor wafer captures the light, converting it into free electrons and holes — positively charged gaps left behind when electrons are liberated by the light. The nanostructures are peppered with nanoscale balls of metal, 1/2000th of a millimeter across, that use those electrons and holes to help direct the reaction.

A simple insulating layer atop the panel keeps the temperature at a toasty 75 degrees Celsius, or 167 degrees Fahrenheit, warm enough to help encourage the reaction while also being cool enough for the semiconductor catalyst to perform well. The outdoor version of the experiment, with less reliable sunlight and temperature, achieved 6.1% efficiency at turning the energy from the sun into hydrogen fuel. However, indoors, the system achieved 9% efficiency. The next challenges the team intends to tackle are to further improve the efficiency and to achieve ultrahigh purity hydrogen that can be directly fed into fuel cells.

Photoelectrochemical CO2-to-fuel conversion with simultaneous plastic reforming

by Subhajit Bhattacharjee, Motiar Rahaman et al. in Nature Synthesis

Researchers have developed a system that can transform plastic waste and greenhouse gases into sustainable fuels and other valuable products — using just the energy from the Sun. The researchers, from the University of Cambridge, developed the system, which can convert two waste streams into two chemical products at the same time — the first time this has been achieved in a solar-powered reactor.

The reactor converts the carbon dioxide (CO2) and plastics into different products that are useful in a range of industries. 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. The system can easily be tuned to produce different products by changing the type of catalyst used in the reactor.

Converting plastics and greenhouse gases — two of the biggest threats facing the natural world — into useful and valuable products using solar energy is an important step in the transition to a more sustainable, circular economy.

“Converting waste into something useful using solar energy is a major goal of our research,” said Professor Erwin Reisner from the Yusuf Hamied Department of Chemistry, the paper’s senior author. “Plastic pollution is a huge problem worldwide, and often, many of the plastics we throw into recycling bins are incinerated or end up in landfill.”

Reisner also leads the Cambridge Circular Plastics Centre (CirPlas), which aims to eliminate plastic waste by combining blue-sky thinking with practical measures. Other solar-powered ‘recycling’ technologies hold promise for addressing plastic pollution and for reducing the amount of greenhouse gases in the atmosphere, but to date, they have not been combined in a single process.

“A solar-driven technology that could help to address plastic pollution and greenhouse gases at the same time could be a game-changer in the development of a circular economy,” said Subhajit Bhattacharjee, the paper’s co-first author.

“We also need something that’s tuneable, so that you can easily make changes depending on the final product you want,” said co-first author Dr Motiar Rahaman.

The researchers developed an integrated reactor with two separate compartments: one for plastic, and one for greenhouse gases. The reactor uses a light absorber based on perovskite — a promising alternative to silicon for next-generation solar cells. The team designed different catalysts, which were integrated into the light absorber. By changing the catalyst, the researchers could then change the end product. Tests of the reactor under normal temperature and pressure conditions showed that the reactor could efficiently convert PET plastic bottles and CO2 into different carbon-based fuels such as CO, syngas or formate, in addition to glycolic acid. The Cambridge-developed reactor produced these products at a rate that is also much higher than conventional photocatalytic CO2 reduction processes.

“Generally, CO2 conversion requires a lot of energy, but with our system, basically you just shine a light at it, and it starts converting harmful products into something useful and sustainable,” said Rahaman. “Prior to this system, we didn’t have anything that could make high-value products selectively and efficiently.”

“What’s so special about this system is the versatility and tuneability — we’re making fairly simple carbon-based molecules right now, but in future, we could be able to tune the system to make far more complex products, just by changing the catalyst,” said Bhattacharjee.

Reisner recently received new funding from the European Research Council to help the development of their solar-powered reactor. Over the next five years, they hope to further develop the reactor to produce more complex molecules. The researchers say that similar techniques could someday be used to develop an entirely solar-powered recycling plant.

“Developing a circular economy, where we make useful things from waste instead of throwing it into landfill, is vital if we’re going to meaningfully address the climate crisis and protect the natural world,” said Reisner. “And powering these solutions using the Sun means that we’re doing it cleanly and sustainably.”

Data Centers on Wheels: Emissions From Computing Onboard Autonomous Vehicles

by Soumya Sudhakar, Vivienne Sze, Sertac Karaman in IEEE Micro

In the future, the energy needed to run the powerful computers on board a global fleet of autonomous vehicles could generate as many greenhouse gas emissions as all the data centers in the world today. That is one key finding of a new study from MIT researchers that explored the potential energy consumption and related carbon emissions if autonomous vehicles are widely adopted.

The data centers that house the physical computing infrastructure used for running applications are widely known for their large carbon footprint: They currently account for about 0.3 percent of global greenhouse gas emissions, or about as much carbon as the country of Argentina produces annually, according to the International Energy Agency. Realizing that less attention has been paid to the potential footprint of autonomous vehicles, the MIT researchers built a statistical model to study the problem. They determined that 1 billion autonomous vehicles, each driving for one hour per day with a computer consuming 840 watts, would consume enough energy to generate about the same amount of emissions as data centers currently do.

The researchers also found that in over 90 percent of modeled scenarios, to keep autonomous vehicle emissions from zooming past current data center emissions, each vehicle must use less than 1.2 kilowatts of power for computing, which would require more efficient hardware. In one scenario — where 95 percent of the global fleet of vehicles is autonomous in 2050, computational workloads double every three years, and the world continues to decarbonize at the current rate — they found that hardware efficiency would need to double faster than every 1.1 years to keep emissions under those levels.

“If we just keep the business-as-usual trends in decarbonization and the current rate of hardware efficiency improvements, it doesn’t seem like it is going to be enough to constrain the emissions from computing onboard autonomous vehicles. This has the potential to become an enormous problem. But if we get ahead of it, we could design more efficient autonomous vehicles that have a smaller carbon footprint from the start,” says first author Soumya Sudhakar, a graduate student in aeronautics and astronautics.

The researchers built a framework to explore the operational emissions from computers on board a global fleet of electric vehicles that are fully autonomous, meaning they don’t require a back-up human driver. The model is a function of the number of vehicles in the global fleet, the power of each computer on each vehicle, the hours driven by each vehicle, and the carbon intensity of the electricity powering each computer.

“On its own, that looks like a deceptively simple equation. But each of those variables contains a lot of uncertainty because we are considering an emerging application that is not here yet,” Sudhakar says.

For instance, some research suggests that the amount of time driven in autonomous vehicles might increase because people can multitask while driving and the young and the elderly could drive more. But other research suggests that time spent driving might decrease because algorithms could find optimal routes that get people to their destinations faster. In addition to considering these uncertainties, the researchers also needed to model advanced computing hardware and software that doesn’t exist yet.

To accomplish that, they modeled the workload of a popular algorithm for autonomous vehicles, known as a multitask deep neural network because it can perform many tasks at once. They explored how much energy this deep neural network would consume if it were processing many high-resolution inputs from many cameras with high frame rates, simultaneously. When they used the probabilistic model to explore different scenarios, Sudhakar was surprised by how quickly the algorithms’ workload added up. For example, if an autonomous vehicle has 10 deep neural networks processing images from 10 cameras, and that vehicle drives for one hour a day, it will make 21.6 million inferences each day. One billion vehicles would make 21.6 quadrillion inferences. To put that into perspective, all of Facebook’s data centers worldwide make a few trillion inferences each day (1 quadrillion is 1,000 trillion).

“After seeing the results, this makes a lot of sense, but it is not something that is on a lot of people’s radar. These vehicles could actually be using a ton of computer power. They have a 360-degree view of the world, so while we have two eyes, they may have 20 eyes, looking all over the place and trying to understand all the things that are happening at the same time,” Karaman says.

Autonomous vehicles would be used for moving goods, as well as people, so there could be a massive amount of computing power distributed along global supply chains, he says. And their model only considers computing — it doesn’t take into account the energy consumed by vehicle sensors or the emissions generated during manufacturing.

To keep emissions from spiraling out of control, the researchers found that each autonomous vehicle needs to consume less than 1.2 kilowatts of energy for computing. For that to be possible, computing hardware must become more efficient at a significantly faster pace, doubling in efficiency about every 1.1 years. One way to boost that efficiency could be to use more specialized hardware, which is designed to run specific driving algorithms. Because researchers know the navigation and perception tasks required for autonomous driving, it could be easier to design specialized hardware for those tasks, Sudhakar says. But vehicles tend to have 10- or 20-year lifespans, so one challenge in developing specialized hardware would be to “future-proof” it so it can run new algorithms.

In the future, researchers could also make the algorithms more efficient, so they would need less computing power. However, this is also challenging because trading off some accuracy for more efficiency could hamper vehicle safety. Now that they have demonstrated this framework, the researchers want to continue exploring hardware efficiency and algorithm improvements. In addition, they say their model can be enhanced by characterizing embodied carbon from autonomous vehicles — the carbon emissions generated when a car is manufactured — and emissions from a vehicle’s sensors. While there are still many scenarios to explore, the researchers hope that this work sheds light on a potential problem people may not have considered.

“We are hoping that people will think of emissions and carbon efficiency as important metrics to consider in their designs. The energy consumption of an autonomous vehicle is really critical, not just for extending the battery life, but also for sustainability,” says Sze.

Unravelling the Interfacial Dynamics of Bandgap Funneling in Bismuth‐Based Halide Perovskites

by Yunqi Tang, Chun Hong Mak, Jun Zhang, Guohua Jia, Kuan‐Chen Cheng, Haisheng Song, Mingjian Yuan, Shijun Zhao, Ji‐Jung Kai, Juan Carlos Colmenares, Hsien‐Yi Hsu in Advanced Materials

The conversion of solar energy into hydrogen energy represents a promising and green technique for addressing the energy shortage and reducing fossil fuel emissions. A research team from City University of Hong Kong (CityU) recently developed a lead-free perovskite photocatalyst that delivers highly efficient solar energy-to-hydrogen conversion.

Most importantly, they unveiled the interfacial dynamics of solid-solid (between halide perovskite molecules) and solid-liquid (between a halide perovskite and an electrolyte) interfaces during photoelectrochemical hydrogen production. The latest findings open up an avenue to develop a more efficient solar-driven method for producing hydrogen fuel in the future.

Hydrogen is considered to be a better and more promising renewable energy alternative due to its abundance, high energy density, and environmental friendliness. Apart from photoelectrochemical water splitting, another promising method of producing hydrogen is by splitting hydrohalic acid using solar-driven photocatalysts. But the long-term stability of photocatalysts is a critical challenge, as most catalysts made of transition metal oxides or metal are unstable under acidic conditions.

a) Powder X-ray diffraction (XRD) patterns of MBI and MBCl-I. b,c) SEM image of MBCl-I (b) and MBI (c) photoelectrodes. d) Crystal-structural model of the MBI. e,f) Band structure of MBCl-I (e) and MBI (f). g) UV–vis diffuse reflectance spectra of MBCl-I and MBI. h,i) Density of states (DOS) of MBCl-I (h) and MBI (i).

“Lead-based hybrid perovskites are used to overcome this stability issue, but the high solubility in water and toxicity of lead limits their potential for widespread applications,” explained Dr Sam Hsu Hsien-Yi, Assistant Professor in the School of Energy and Environment and the Department of Materials Science and Engineering at CityU. “Bismuth-based perovskites, in contrast, have been confirmed to provide a non-toxic, chemically stable alternative for solar-fuel applications, but the photocatalytic efficiency needs to be enhanced.”

Motivated to design an efficient and stable photocatalyst, Dr Hsu and his collaborators recently developed a bismuth-based halide perovskite with a structure of bandgap funneling for highly efficient charge-carrier transport. It is a mixed-halide perovskite, in which the distribution of iodide ions gradually decreases from the surface to the interior, forming a bandgap funnel structure, which promotes a photo-induced charge transfer from the interior to the surface for an efficient photocatalytic redox reaction. This newly designed perovskite has high solar energy conversion efficiency, exhibiting a hydrogen generation rate enhanced up to about 341 ± 61.7 µmol h−1 with a platinum co-catalyst under visible light irradiation. The findings were published half a year ago.

But Dr Hsu’s team did not stop there. “We wanted to explore the dynamic interactions between the halide perovskite molecules and those at the interface between the photoelectrode and the electrolyte, which remained unknown,” said Dr Hsu. “Since photoelectrochemical hydrogen production involves a catalytic process, highly effective hydrogen generation can be achieved by intense light absorption using a semiconductor as a photocatalyst with a suitable energy band structure and efficient charge separation, facilitated by an external electrical field formed near the semiconductor-liquid interface.”

Cyclic voltammogram of a) MBCl-I and d) MBI in CH2Cl2 with 1 × 10−3 m TBAPF6 at various scan rates. Reduction peak current vs ν1/2 of b) MBCl-I and e) MBI. Oxidation peak current versus ν1/2 of c) MBCl-I and f) MBI.

To discover the exciton transfer dynamics, the team utilised temperature-dependent time-resolved photoluminescence to analyse the energy transportation of electron-hole pairs between the perovskite molecules. They also evaluated the diffusion coefficient and electron transfer rate constant of halide perovskite materials in the solution to illustrate the effectiveness of electron transport through the solid-liquid interfaces between a perovskite-based photoelectrode and the electrolyte. “We demonstrated how our newly designed photocatalyst can effectively achieve high-performance photoelectrochemical hydrogen generation as a result of efficient charge transfer,” said Dr Hsu.

In the experiment, the team also proved that bandgap funneling structured halide perovskites had a more efficient charge separation and transfer process between the interface of the electrode and electrolyte. The improved charge separation can drive the migration of charge carriers onto the surface of halide perovskites deposited on the conductive glasses as the photoelectrode, allowing faster photoelectrochemical activity on the photoelectrode’s surface. Consequently, the effective charge transfer inside the bandgap funnel structured halide perovskites exhibited enhanced photocurrent density under light irradiation.

“Uncovering the interfacial dynamics of these novel materials during the process of photoelectrochemical hydrogen generation is a crucial breakthrough,” explained Dr Hsu. “An in-depth understanding of the interfacial interactions between halide perovskites and liquid electrolytes can build a scientific foundation for researchers in this field to further investigate the development of alternative and useful materials for solar-induced hydrogen production.”

A ligand insertion mechanism for cooperative NH3 capture in metal–organic frameworks

by Benjamin E. R. Snyder, Ari B. Turkiewicz, Hiroyasu Furukawa, Maria V. Paley, Ever O. Velasquez, Matthew N. Dods, Jeffrey R. Long in Nature

Industrial production of ammonia, primarily for synthetic fertilizer — the fuel for last century’s Green Revolution — is one of the world’s largest chemical markets, but also one of the most energy intensive.

Globally, the Haber-Bosch process for making ammonia uses about 1% of all fossil fuels and produces 1% of all carbon dioxide emissions, making it a major contributor to climate change. Now, University of California, Berkeley, chemists have taken a big step toward making ammonia production more environmentally friendly: a “greener” ammonia for “greener” fertilizer.

A major stumbling block to making ammonia with less energy input has been separating the ammonia from the reactants — primarily nitrogen and hydrogen — without the large temperature and pressure swings required by the Haber-Bosch process. That reaction takes place between about 300 and 500 degrees Celsius, but ammonia is removed by cooling the gas to approximately -20 C, at which point the gaseous ammonia condenses as a liquid. The process also requires pressurizing the reactants to about 150–300 times atmospheric pressure. All this takes fossil fuel energy.

Alternative methods for ammonia separation could open the door to alternative processes operating under less extreme conditions. To address this problem, UC Berkeley chemists designed and synthesized porous materials — metal-organic frameworks, or MOFs — that bind and release ammonia at moderate pressures and temperatures around 175 C. Because the MOF doesn’t bind to any of the reactants, the capture and release of ammonia can be accomplished with smaller temperature swings, thus saving energy.

“A big challenge to decarbonizing fertilizer production is finding a material where you can capture and then release very large quantities of ammonia, ideally with a minimal input of energy,” said UC Berkeley postdoctoral fellow Benjamin Snyder, who led the research. “That is to say, you don’t want to have to put a lot of heat in your material to force the ammonia to come off, and likewise, when the ammonia absorbs, you don’t want that to generate a lot of waste heat.”

One key advantage of a process that operates at lower temperatures and pressures is that ammonia, and thus fertilizer, could be produced at smaller facilities closer to farmers — even onsite at the farm — rather than at large, centralized chemical plants.

“The dream here would be enabling a technology where a farmer in some economically disadvantaged area of the world now has much more ready access to the ammonia that they need to grow their crops,” Snyder said. “To be clear, our material hasn’t gone and solved that problem outright. But we’ve put forward a new way of thinking about how you can use metal-organic frameworks in the context of ammonia capture for a modified Haber-Bosch process. I think this study represents a really important conceptual advance in that direction.”

Snyder and Jeffrey Long, the paper’s senior author and a UC Berkeley professor of chemistry of chemical and biomolecular engineering, will publish the details of their study.

“This work is of fundamental importance because it reveals a new cooperative mechanism for selective gas capture,” said Long, the C. Judson King Distinguished Professor at UC Berkeley and a faculty scientist at Lawrence Berkeley National Laboratory. “We are optimistic that the mechanism will extend to other molecules of industrial significance that have a strong affinity for binding metals.”

A cross-section through a porous metal-organic framework, showing the copper atoms (orange) that are constrained in a rigid structure by organic linker molecules, cyclohexanedicarboxylate, that contain oxygen (red) and carbon (gray). Ammonia cleaves the copper-oxygen bonds in this 3D framework, causing it to transform into a one-dimensional polymer. The porous, 3D framework then reassembles itself as ammonia is driven off. (Image credit: Jeffrey Long lab, UC Berkeley)

According to Snyder, many researchers are working on ways to make the Haber-Bosch process — which dates from the early 20th century — more sustainable. This includes producing one major reactant, hydrogen, using solar power to split water into hydrogen and oxygen. Today, hydrogen is typically obtained from natural gas, which is mostly methane, in a reaction that releases carbon dioxide, the dominant greenhouse gas. Other green modifications include novel catalysts that operate at lower temperatures and pressures to react hydrogen with nitrogen — typically captured from the air — to form ammonia, NH3.

But removing ammonia from the mixture after the reaction has remained difficult. Other porous materials, such as zeolites, are unable to absorb and release large quantities of ammonia. And other MOFs that people tried often disintegrated in the presence of ammonia, which is highly corrosive. Snyder’s innovation was to try a relatively new variety of MOF that employs copper atoms linked by organic molecules called cyclohexanedicarboxylate to create the rigid and highly porous MOF structure. To his surprise, ammonia didn’t destroy this MOF, but converted it into strands of a copper and ammonia-containing polymer that has an extremely high density of stored ammonia. Moreover, the polymer strands easily gave up their bound ammonia at relatively low temperatures, restoring the material to its initial rigid, porous MOF structure in the process.

“When you expose this framework to ammonia, it completely changes its structure,” he said. “It starts as a porous, three-dimensional material, and upon being exposed to ammonia, it actually unweaves itself and forms what I would call a one-dimensional polymer. Think of it like a bundle of strings. This really unusual adsorption mechanism allows us to uptake huge quantities of ammonia.”

In the reverse process, he added, “the polymer somehow will weave itself back into a three-dimensional framework when you remove the ammonia, which I think is one of the most arresting features of this material.” Snyder found that the MOF could be tuned to absorb and release ammonia under a large range of pressures, making it more adaptable to whatever reaction conditions turn out to be best for producing ammonia most efficiently from sustainable reactants.

“The benefit of our MOFs is that we’ve discovered that they can be rationally tuned, which means that if you end up locking in on a certain set of reaction conditions in a specific process, we can modify the MOF’s performance parameters — the temperature that you use and the pressure that you use for this adsorbent — to closely match up with the specific application.”

Snyder emphasized that ammonia capture is just one part of any modified process to make greener ammonia, which is still a work in progress.

“There are lots of smart people thinking about catalyst and reactor design for a modified Haber Bosch process that’s designed to operate under more moderate temperatures and pressures,” Snyder said. “Where we come in is, after you’ve made the ammonia, our materials are what you would try to use to separate and capture the ammonia under these new reaction conditions.”

Underground Gravity Energy Storage: A Solution for Long-Term Energy Storage

by Julian David Hunt, Behnam Zakeri, Jakub Jurasz, Wenxuan Tong, Paweł B. Dąbek, Roberto Brandão, Epari Ritesh Patro, Bojan Đurin, Walter Leal Filho, Yoshihide Wada, Bas van Ruijven, Keywan Riahi in Energies

A novel technique called Underground Gravity Energy Storage turns decommissioned mines into long-term energy storage solutions, thereby supporting the sustainable energy transition.

Renewable energy sources are central to the energy transition toward a more sustainable future. However, as sources like sunshine and wind are inherently variable and inconsistent, finding ways to store energy in an accessible and efficient way is crucial. While there are many effective solutions for daily energy storage, the most common being batteries, a cost-effective long-term solution is still lacking.

In a new IIASA-led study, an international team of researchers developed a novel way to store energy by transporting sand into abandoned underground mines. The new technique called Underground Gravity Energy Storage (UGES) proposes an effective long-term energy storage solution while also making use of now-defunct mining sites, which likely number in the millions globally.

Underground Gravity Energy Storage system: A schematic of different system sections.

UGES generates electricity when the price is high by lowering sand into an underground mine and converting the potential energy of the sand into electricity via regenerative braking and then lifting the sand from the mine to an upper reservoir using electric motors to store energy when electricity is cheap. The main components of UGES are the shaft, motor/generator, upper and lower storage sites, and mining equipment. The deeper and broader the mineshaft, the more power can be extracted from the plant, and the larger the mine, the higher the plant’s energy storage capacity.

“When a mine closes, it lays off thousands of workers. This devastates communities that rely only on the mine for their economic output. UGES would create a few vacancies as the mine would provide energy storage services after it stops operations,” says Julian Hunt, a researcher in the IIASA Energy, Climate, and Environment Program and the lead author of the study. “Mines already have the basic infrastructure and are connected to the power grid, which significantly reduces the cost and facilitates the implementation of UGES plants.”

Other energy storage methods, like batteries, lose energy via self-discharge over long periods. The energy storage medium of UGES is sand, meaning that there is no energy lost to self-discharge, enabling ultra-long time energy storage ranging from weeks to several years.

A submillimeter bundled microtubular flow battery cell with ultrahigh volumetric power density

by Yutong Wu, Fengyi Zhang, Ting Wang, Po-Wei Huang, Alexandros Filippas, Haochen Yang, Yanghang Huang, Chao Wang, Huitian Liu, Xing Xie, Ryan P. Lively, Nian Liu in Proceedings of the National Academy of Sciences

Clean energy is the leading solution for climate change. But solar and wind power are inconsistent at producing enough energy for a reliable power grid. Alternatively, lithium-ion batteries can store energy but are a limited resource.

“The advantage of a coal power plant is it’s very steady,” said Nian Liu, an assistant professor at the Georgia Institute of Technology. “If the power source fluctuates like it does with clean energy, it makes it more difficult to manage, so how can we use an energy storage device or system to smooth out these fluctuations?”

Flow batteries offer a solution. Electrolytes flow through electrochemical cells from storage tanks in this rechargeable battery. The existing flow battery technologies cost more than $200/kilowatt hour and are too expensive for practical application, but Liu’s lab in the School of Chemical and Biomolecular Engineering (ChBE) developed a more compact flow battery cell configuration that reduces the size of the cell by 75%, and correspondingly reduces the size and cost of the entire flow battery. The work could revolutionize how everything from major commercial buildings to residential homes are powered.

Liu’s lab in the School of Chemical and Biomolecular Engineering (ChBE) developed a more compact flow battery cell configuration that reduces the size of the cell by 75%, and correspondingly reduces the size and cost of the entire flow battery.

Flow batteries get their name from the flow cell where electron exchange happens. Their conventional design, the planar cell, requires bulky flow distributors and gaskets, increasing size and cost but decreasing overall performance. The cell itself is also expensive. To reduce footprint and cost, the researchers focused on improving the flow cell’s volumetric power density (W/L-of-cell). They turned to a configuration commonly used in chemical separation — sub-millimeter, bundled microtubular (SBMT) membrane — made of a fiber-shaped filter membrane known as a hollow fiber. This innovation has a space-saving design that can mitigate pressure across the membranes that ions pass through without needing additional support infrastructure.

“We were interested in the effect of the battery separator geometry on the performance of flow batteries,” said Ryan Lively, a professor in ChBE. “We were aware of the advantages that hollow fibers imparted on separation membranes and set out to realize those same advantages in the battery field.”

Applying this concept, the researchers developed an SMBT that reduces membrane-to-membrane distance by almost 100 times. The microtubular membrane in the design works as an electrolyte distributor at the same time without the need for large supporting materials. The bundled microtubes create a shorter distance between electrodes and membranes, increasing the volumetric power density. This bundling design is the key discovery for maximizing flow batteries’ potential.

To validate their new battery configuration, the researchers used four different chemistries: vanadium, zinc-bromide, quinone-bromide, and zinc-iodide. Although all chemistries are functional, two were most promising. Vanadium was the most mature chemistry, but also less accessible, and the reduced form of it is unstable in air. They found zinc iodide was the most energy-dense option, making it the most effective for residential units. Zinc-iodide offered many advantages even compared to lithium: It has less of a supply chain issue and also can be turned into zinc oxide and dissolve in acid, making it much easier to recycle. This electrochemical solution for this unique shape of the flow battery proved more powerful than conventional planar cells.

“The superior performance of the SMBT was also demonstrated by finite element analysis,” said Xing Xie, an assistant professor in the School of Civil and Environmental Engineering. “This simulation method will also be applied in our future study for cell performance optimization and scaling up.”

With zinc-iodide chemistry, the battery could run for more than 220 hours, or to > 2,500 cycles at off-peak conditions. It could also potentially reduce the cost from $800 to less than $200 per kilowatt hour by using recycled electrolyte.

The researchers are already working on commercialization, focusing on developing batteries with different chemistries like vanadium and scaling up their size. Scaling will require coming up with an automated process to manufacture a hollow fiber module, which now is done manually, fiber by fiber. They eventually hope to deploy the battery in Georgia Tech’s 1.4-megawatt microgrid in Tech Square, a project that tests microgrid integration into the power grid and offers living laboratory for professors and students. The SBMT cells could also be applied to different energy storage systems like electrolysis and fuel cells. The technology could even be strengthened with advanced materials and different chemistry in various applications.

“This innovation is very application driven,” Liu said. “We have the need to reach carbon neutrality by increasing the percentage of renewable energy in our energy generation, and right now, it’s less than 15% in the U.S. Our research could change this.”

Plastic photodegradaton under simulated marine concitions

by Annalisa Delre, Maaike Goudriaan, et al in Marine Pollution Bulletin

UV light from the sun slowly breaks down plastics on the ocean’s surfaces. Floating microplastic is broken down into ever smaller, invisible nanoplastic particles that spread across the entire water column, but also to compounds that can then be completely broken down by bacteria. This is shown by experiments in the laboratory of the Royal Netherlands Institute for Sea Research, NIOZ, on Texel. PhD student Annalisa Delre and colleagues calculate that about two percent of visibly floating plastic may disappears from the ocean surface in this way each year.

“This may seem small, but year after year, this adds up. Our data show that sunlight could thus have degraded a substantial amount of all the floating plastic that has been littered into the oceans since the 1950s,” says Delre.

Since the mass production of plastics began in the 1950s, a significant portion of plastic waste has made its way to the ocean via rivers, blown of from land by winds or directly dumped from ships. But the amount of plastic that is actually found in the ocean is only a fraction of what has entered the ocean. The majority is literally lost. In science, this problem is known as the Missing Plastic Paradox. To investigate if degradation by UV light can explain some of the vanished plastic, Delre and colleagues conducted experiments in the laboratory.

In a container filled with simulated seawater, the researchers mixed small plastic pieces. They then stirred this plastic soup automatically under a lamp that mimiced UV light from the sun. Gases and dissolved compounds including nanoplastics that leached from the degrading plastic pieces were then captured and analysed.

From these measurements, the researchers measured that at least 1.7 percent of (visible) microplastics break down annually. For the most part it breaks down into ever smaller pieces including the (invisible) nanoplastics as well as into molecules that one also finds in crude oil. Potentially, some of these can be broken down further by bacteria. Only a small fraction is fully oxidized to the relatively harmless CO2. Fed into a more complex calculation, accounting for the release of floating plastic to the ocean, beaching and ongoing photodegradation at the ocean surface, the breakdown by sunlight could have transformed a fifth (22%) of all floating plastic that has ever been released to the ocean, mostly to smaller, dissolved particles and compounds.

“With these calculations, we put an important piece in the jigsaw of the Missing Plastic Paradox in place,” says Helge Niemann, researcher at NIOZ and professor at Utrecht University and one of the supervisors of PhD student Delre.

Release of photodegradation products from PE (A, B, C), PP (D, E), PS (F) and PET (G) upon irradiation with UV light.

Potentially, there may be good news in this research, says Niemann. “In part, the plastic breaks down into substances that can be completely broken down by bacteria. But for another part, the plastic remains in the water as invisible nanoparticles.” In an earlier study with ‘real’ Wadden Sea water and North Sea water, Niemann and colleagues already showed that a substantial part of the missing plastics floats in the oceans as invisible nanoparticles.

“The precise effects of these particles on algae, fish and other life in the oceans are still largely unclear,” says Niemann.

“With these experiments under UV light, we can explain another part of the plastic paradox. We need to continue investigating the fate of the remaining plastic. Also, we need to investigate what all this micro and nano plastic does to marine life. Even more important,” Niemann stresses, “is to stop plastic littering all together, as this thickens the ocean’s plastic soup.”

Synergistic and Antagonistic Effects of the Co-Pyrolysis of Plastics and Corn Stover to Produce Char and Activated Carbon

by Mark Gale, Peter M. Nguyen, Kandis Leslie Gilliard-AbdulAziz in ACS Omega

University of California, Riverside, scientists have moved a step closer to finding a use for the hundreds of millions of tons of plastic waste produced every year that often winds up clogging streams and rivers and polluting our oceans.

In a recent study, Kandis Leslie Abdul-Aziz, a UCR assistant professor of chemical and environmental engineering, and her colleagues detailed a method to convert plastic waste into a highly porous form of charcoal or char that has a whopping surface area of about 400 square meters per gram of mass. Such charcoal captures carbon and could potentially be added to soil to improve soil water retention and aeration of farmlands. It could also fertilize the soil as it naturally breaks down. Abdul-Aziz, however, cautioned that more work needs to be done to substantiate the utility of such char in agriculture.

The plastic-to-char process was developed at UC Riverside’s Marlan and Rosemary Bourns College of Engineering. It involved mixing one of two common types of plastic with corn waste — the leftover stalks, leaves, husks, and cobs — collectively known as corn stover. The mix was then cooked with highly compressed hot water, a process known as hydrothermal carbonization. The highly porous char was produced using polystyrene, the plastic used for Styrofoam packaging, and polyethylene terephthalate, or PET, the material commonly used to make water and soda bottles, among many other products.

The char and activated carbon making process.

The study followed an earlier successful effort to use corn stover alone to make activated charcoal used to filter pollutants from drinking water. In the earlier study, charcoal made from corn stover alone activated with potassium hydroxide was able to absorb 98% of the pollutant vanillin from test water samples. In the follow-up study, Abdul-Aziz and her colleagues wanted to know if activated charcoal made from a combination of corn stover and plastic also could be an effective water treatment medium. If so, plastic waste could be repurposed to clean up water pollution. But the activated charcoal made from the mix absorbed only about 45% of vanillin in test water samples — making it ineffective for water cleanups, she said.

“We theorize that there could be still some residual plastic on the surface of the materials, which is preventing the absorption of some of these (vanillin) molecules on the surface,” she said.

Still, the ability to make highly porous charcoal by combining plastic and plant biomass waste is an important discovery, as detailed in the paper. The lead author is Mark Gale, a former UCR doctoral student who is now a lecturer at Harvey Mudd College. UCR undergraduate student Peter Nguyen is a co-author and Abdul-Aziz is the corresponding author.

“It could be a very useful biochar because it is a very high surface area material,” Abdul-Aziz said. “So, if we just stop at the char and not make it in that turn into activated carbon, I think there are a lot of useful ways that we can utilize it.”

Plastic is essentially a solid form of petroleum that accumulates in the environment, where it pollutes, entangles, and chokes and kills fish, birds, and other animals that inadvertently ingest it. Plastics also break down into micro particles that can get into our bodies and damage cells or induce inflammatory and immune reactions. Unfortunately, it costs more to recycle used plastic than it costs to make new plastic from petroleum. Abdul-Aziz’s laboratory takes a different approach to recycling. It is devoted to putting pernicious waste products such as plastic and plant biomass waste back into the economy by upcycling them into valuable commodities.

“I feel like we have more of an agnostic approach to plastic recycling when you can throw it in (with biomass) and use the char to better the soil,” she said. “That’s what we’re thinking.”

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