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GT/ Efficient organic solar cells processed from green solvents

Energy & green technology biweekly vol.13, 20th November — 4th December


  • A small guest molecule in the right place makes it possible to produce energy-efficient organic solar cells using eco-friendly solvents. A record efficiency of over 17% is demonstrated. In addition, solar cells with larger areas can be produced.
  • Scientists describe the development of a cost-effective Scotch-tape-like film that can be applied to perovskite solar cells and capture 99.9% of leaked lead in the event of solar cell damage.
  • Researchers have used a suite of microscopy methods to visualize why perovskite materials are seemingly so tolerant of defects in their structure.
  • Scientists have published an analysis laying out how the tiny beads of glass inside many meteorites came to be — and what they can tell us about what happened in the early solar system.
  • Alternative-energy research is charting a path toward the mass adoption of clean cars powered by direct-ethanol fuel cells.
  • A new technological advancement uses an electric field to achieve efficient and low-cost ammonia removal from wastewater.
  • Researchers have developed a novel method to fabricate lead halide perovskite solar cells with record efficiency.
  • A new study has identified serpentinite — a green rock that looks a bit like snakeskin and holds fluids in its mineral structures — as a key driver of the oxygen recycling process, which helped create and maintain the sustaining atmosphere for life on Earth.
  • Cost-slashing innovations are underway in the electric power sector and could give electricity the lead over fossil-based combustion fuels in the world’s energy supply by mid-century. When combined with a global carbon price, these developments can catalyze emission reductions to reach the Paris climate targets, while reducing the need for controversial negative emissions, a new study finds.
  • New research gives a view of the scale of plastic creation globally, tracing where it’s produced, where it ends up, and its environmental impact.
  • 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.

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Latest Research

A guest-assisted molecular-organization approach for >17% efficiency organic solar cells using environmentally friendly solvents

by Haiyang Chen, Rui Zhang, Xiaobin Chen, Guang Zeng, Libor Kobera, Sabina Abbrent, Ben Zhang, Weijie Chen, Guiying Xu, Jiyeon Oh, So-Huei Kang, Shanshan Chen, Changduk Yang, Jiri Brus, Jianhui Hou, Feng Gao, Yaowen Li, Yongfang Li in Nature Energy

A small guest molecule in the right place makes it possible to produce energy-efficient organic solar cells using eco-friendly solvents. A record efficiency over 17% is demonstrated. In addition, solar cells with larger areas can be produced. “This is a major step towards large-scale industrial manufacture of efficient and stable organic solar cells,” says Feng Gao, professor in the Department of Physics, Chemistry and Biology (IFM) at Linköping University.

Developments in organic solar cells are rapid, and the maximum energy efficiency achieved by solar cells produced in the laboratory is currently over 18%. The energy efficiency measures how large a fraction of the energy in sunlight is converted to useful energy in the solar cells. The efficiency limit is considered to be around 24% for organic solar cells.

Chemical structures and structural characterization of the acceptors.

One challenge is to manufacture organic solar cells that are sufficiently stable to function for ten years or more. Another challenge is that the highest energy is achieved in solar cells manufactured in solutions that contain toxic solvents, with a relatively low boiling point. The low boiling point causes problems during the manufacture, since the solution evaporates slightly too rapidly. The use of more eco-friendly solvents with higher boiling points leads immediately to a decrease in energy efficiency. This is a dilemma that researchers all over the world are working to solve.

These problems have now been solved in a joint project led by researchers at Linköping University in Sweden and Soochow University in China.

Schematic illustration of BTO-enabling formation of highly crystalline Y6 from high-boiling-point solvents.

They have managed to manufacture a solar cell, using a solution with a high boiling point and without any toxic ingredients, whose energy efficiency is better than 17%. In addition, the green-solvent processed solar module with an area of 36 cm2 shows a power conversion efficiency over 14%. This is the highest efficiency reported to date for organic solar cell modules with an active area exceeding 20 cm2. Both of these breakthroughs are important for organic solar cell technology to make its commercial breakthrough at a large scale.

“Our results now open for the manufacture of organic solar cells at larger scales for outdoor use,” says postdoc Rui Zhang, who works with Professor Feng Gao in the Electronic and Photonic Materials Division, Linköping University.

Photovoltaic performance of the devices.

The function of organic solar cells has improved step-by-step. When sunlight in the form of photons is absorbed in an organic semiconducting donor, an “excited state” forms. Electrons jump to a higher energy level and create holes at the lower energy level, to which they are, however, still attracted. The electrons are not fully freed, and a photocurrent does not arise. The researchers conducted experiments in which they added various acceptor materials, which accept electrons and thus allow them to become free, giving rise to a photocurrent.

Non-halogenated solvent-processed module and device stability.

A couple of years ago, Chinese researchers developed a new acceptor material, named Y6, which can deliver high efficiency for organic solar cells.

What the work described in this joint publication has now achieved is to find a guest molecule, known as BTO, that ensures that Y6 molecules in the solar cell are packed in such a close and stable manner in the green solvents that the photocurrent can be generated efficiently. Adding BTO also enables larger areas of the solar cells to be manufactured with high efficiency.

“Our strategy leads to clear design rules for optimising the interaction between organic donors and acceptors in multicomponent blends, meeting the critical requirements for future development of organic photovoltaic technology, says Professor Yaowen Li, Soochow University.

23.7% Efficient inverted perovskite solar cells by dual interfacial modification

by Matteo Degani, Qingzhi An, Miguel Albaladejo-Siguan, Yvonne J. Hofstetter, Changsoon Cho, Fabian Paulus, Giulia Grancini, Yana Vaynzof in Science Advances

Metal halide perovskites have been under intense investigation over the last decade, due to the remarkable rise in their performance in optoelectronic devices such as solar cells or light-emitting diodes. The most efficient devices, fabricated in the so-called ‘standard architecture’ commonly include processing steps performed at high temperature, thus increasing their energy payback time and limiting the possibility to integrate them in emerging applications such as flexible and wearable electronics. An alternative device architecture — termed the ‘inverted architecture’ — eliminates the need for high temperature processing, but generally leads to lower photovoltaic efficiency.

In a joint collaborative effort between the University of Pavia (Italy) and the Technische Universität Dresden (Germany), researchers have developed a novel method to significantly improve the efficiency of inverted architecture solar cells. The method is based on a modification of the interfaces of the perovskite active layer by introducing small amounts of organic halide salts at both the bottom and the top of the perovskite layer. Such organic halide salts, typically used for the formation of two-dimensional perovskites, led to the suppression of microstructural flaws and passivation of the defects of the perovskite layer. Using this approach, the team has achieved a power conversion efficiency of 23.7% — the highest reported to date for an inverted architecture perovskite solar cell.

Chemical structure of PEAI cations and schematics of the fabrication procedure and device architecture used in this work.

“Importantly, the improvement in performance is accompanied by an increase in device stability” says Prof. Giulia Grancini, an Associate Professor of Chemistry at the University of Pavia. Considering that stability remains one of the key hurdles for the commercialization of perovskite solar cells, the simultaneous improvement of efficiency and stability is particularly promising.

“The fact that our devices are fabricated at low temperatures of less than 100° C and that our approach is fully applicable to the fabrication of large-area devices takes us one step closer to large-scale utilization of perovskite solar cells” adds Prof. Yana Vaynzof, Chair for Emerging Electronic Technologies at the Institute for Applied Physics and Photonic Materials and the Center for Advancing Electronics Dresden.

Photovoltaic performance, microstructure, and interfacial composition of the HTL-modified devices.

The record efficiency achieved by the researchers brings perovskite solar cells to new frontiers. Considering the enhanced stability and the scalability of the novel approach, it’s only a matter of time until perovskite solar cells can be found on every rooftop.

Imprint of chondrule formation on the K and Rb isotopic compositions of carbonaceous meteorites

by Nicole X. Nie, Xin-Yang Chen, Timo Hopp, Justin Y. Hu, Zhe J. Zhang, Fang-Zhen Teng, Anat Shahar, Nicolas Dauphas in Science Advances

Ever since scientists started looking at meteorites with microscopes, they’ve been puzzled — and fascinated — by what’s inside. Most meteorites are made of tiny beads of glass that date back to the earliest days of the solar system, before the planets were even formed.

Scientists with the University of Chicago have published an analysis laying out how these beads, which are found in many meteorites, came to be — and what they can tell us about what happened in the early solar system.

“These are big questions,” said UChicago alum Nicole Xike Nie, PhD’19, a postdoctoral fellow at the Carnegie Institution for Science and first author of the study. “Meteorites are snapshots that can reveal the conditions this early dust experienced — which has implications for the evolution of both Earth and other planets.”

Correlations between the isotopic compositions of Rb, K, Te, and Zn in bulk CCs.

The beads of glass inside these meteorites are called chondrules. Scientists think they are bits of rock left over from the debris that was floating around billions of years ago, which eventually coalesced into the planets we now know and love. These are immensely useful to scientists, who can get their hands on pieces of the original stuff that comprised the solar system — before the constant churn of volcanoes and tectonic plates of Earth changed all the rock we can find on the planet itself. But what exactly caused the formation of these chondrules remains unclear.

“We have the same theories we had 50 years ago,” said study co-author and UChicago postdoctoral researcher Timo Hopp. “Even though there have been advances in many other areas, this one has been stubborn.”

Scientists can find clues about the early days of the solar system by looking at the types of a given element in a rock. Elements can come in several different forms, called isotopes, and the proportion in each rock varies according to what happened when that rock was born — how hot it was, whether it cooled slowly or was flash-frozen, what other elements were around to interact with it. From there, scientists can piece together a history of likely events. To try and understand what had happened to the chondrules, Nie, Hopp and other scientists at the Dauphas Origins Lab at UChicago tried applying a unique angle to the isotopes.

First, Nie took extremely rigorous, precise measurements of the concentrations and isotopes of two elements that are depleted in meteorites, potassium and rubidium, which helped narrow down the possibilities of what could have happened in the early solar system. From this information, the team pieced together what must have been happening as the chondrules formed. The elements would have been part of a clump of dust that got hot enough to melt, and then to vaporize. Then, as the material cooled, some of that vapor coalesced back into chondrules.

The model results of condensation during chondrule cooling.

“We can also tell you how fast it cooled, because it was fast enough that not everything condensed,” said Nicolas Dauphas, Professor of Geophysical Sciences at UChicago. “That must mean the temperature was dropping at a rate of around 500 degrees Celsius per hour, which is really fast.”

Based on these constraints, scientists can theorize what kind of event would have been sudden and violent enough to cause this extreme heating and cooling. One scenario that fits would be massive shockwaves passing through the early nebula. “Large planetary bodies nearby can create shocks, which would have heated and then cooled the dust as it passed through,” Dauphas said.

Over the past half-century, people have proposed different scenarios to explain the formation of the chondrules — lightning, or collisions between rocks — but this new evidence tips the balance toward shockwaves as an explanation. This explanation may be the key to understanding a persistent finding that has bedeviled scientists for decades, involving a category of elements that are “moderately volatile,” including potassium and rubidium. The Earth has less of these elements than scientists would expect, based on their general understanding of how the solar system formed. They knew the explanation could be traced to some complex chain of heating and cooling, but no one know the exact sequence. “It’s a huge question in the field of cosmochemistry.” said Dauphas. Now, finally, the team is happy to have put a significant dent in the mystery.

“We know other processes happened — this is just one part of the story — but this really solves one step in the formation of planets,” said Hopp.

Nie agreed: “It’s really cool to be able to say quantitatively, this is what happened.”

On-device lead-absorbing tapes for sustainable perovskite solar cells

by Xun Li, Fei Zhang, Jianxin Wang, Jinhui Tong, Tao Xu, Kai Zhu in Nature Sustainability

Researchers at Northern Illinois University and the U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) in Golden, Colorado, are reporting a potential breakthrough that could help speed commercialization of highly promising perovskite solar cells (PSCs) for use in solar panels.

The scientists describe development of a cost-effective Scotch-tape-like film that can be applied to PSCs and capture 99.9% of leaked lead in the event of solar cell damage.

Pb-absorbing tape fabrication and device integration.

The industry-ready film would help alleviate health and safety concerns without compromising perovskite solar-cell performance or operation, according to the research team. Testing of the lead-absorbing film included submerging damaged cells in water.

“Our practical approach mitigates the potential lead-leakage to a level safer than the standard for drinking water,” said NIU Chemistry Professor Tao Xu, who co-led the research with Kai Zhu of NREL’s National Renewable Energy Laboratory.

“We can easily apply our lead-absorbing materials to off-the-shelf films currently used to encapsulate silicon-based solar cells at the end of their production, so existing fabrication processes for PSCs would not be disrupted,” Xu added. “At the end of PSC production, the films would be laminated to the solar cell.”

An emerging class of solar cells, PSCs are considered rising stars in the field of solar energy because of their high-power conversion efficiency (exceeding 25.5%) and low manufacturing costs. But PSCs are not yet commercially available on a widescale basis because key challenges remain, including potential lead-toxicity issues.

Small amounts of water-soluble lead continue to be essential components to the light-absorbing layer of high efficiency PSCs, which must be able to withstand severe weather for commercial viability. Significant lead leakage from damaged cells would cause health and safety concerns.

Pb leakage tests.

To counter those concerns, the transparent tapes use lead absorbents made with a standard solar ethylene vinyl acetate (EVA) film and a pre-laminated layer of lead-absorbing material. The tape can be attached to both sides of fabricated PSCs, as in the standard encapsulation process used in silicon-based solar cells.

Among the tests used to assess the durability of the new technology, the scientists exposed the film-encapsulated PSCs to outdoor, rooftop conditions for three months. Razor blades and hammers were used to then damage the solar cells before they were submerged in water for seven days. The lead-absorbing tapes exhibited a lead-sequestration efficiency of over 99.9%.

“Perovskite solar cells hold great hope for a more sustainable future,” Xu said. “This work offers a convenient and industry-ready method to diminish the potential lead leakage from lead-containing PSCs, facilitating future commercialization of perovskite-based photovoltaic technology.”

Impact of declining renewable energy costs on electrification in low-emission scenarios

by Gunnar Luderer, Silvia Madeddu, Leon Merfort, Falko Ueckerdt, Michaja Pehl, Robert Pietzcker, Marianna Rottoli, Felix Schreyer, Nico Bauer, Lavinia Baumstark, Christoph Bertram, Alois Dirnaichner, Florian Humpenöder, Antoine Levesque, Alexander Popp, Renato Rodrigues, Jessica Strefler, Elmar Kriegler in Nature Energy

Cost-slashing innovations are underway in the electric power sector and could give electricity the lead over fossil-based combustion fuels in the world’s energy supply by mid-century. When combined with a global carbon price, these developments can catalyse emission reductions to reach the Paris climate targets, while reducing the need for controversial negative emissions, a new study finds.

vKey characteristics of renewables-based electrification and conventional scenarios.

“Today, 80 per cent of all energy demands for industry, mobility or heating buildings is met by burning — mostly fossil — fuels directly, and only 20 per cent by electricity. Our research finds that relation can be pretty much reversed by 2050, making the easy-to-decarbonise electricity the mainstay of global energy supply,” says Gunnar Luderer, author of the new study and researcher the Potsdam Institute for Climate Impact Research as well as professor of Global Energy Systems Analysis at the Technical University of Berlin.

“For the longest time, fossil fuels were cheap and accessible, whilst electricity was the precious and pricier source of energy. Renewable electricity generation — especially from solar photovoltaics — has become cheaper at breath-taking speed, a pace that most climate models have so far underestimated. Over the last decade alone prices for solar electricity fell by 80%, and further cost reductions are expected in the future. This development has the potential to fundamentally revolutionize energy systems. Our computer simulations show that together with global carbon pricing, green electricity can become the cheapest form of energy by 2050, and supply up to three quarters of all demand,” Luderer explains.

Evolution of energy prices at the secondary energy level.

The reasons lie mainly in the ground-breaking technological progress in solar and wind power generation, but also in the end uses of electric energy. Costs per kilowatt hour solar or wind power are steeply falling while battery technology e.g. in cars is improving at great speed. Heat pumps use less energy per unit of heat output than any type of boiler and are becoming increasingly competitive not only in buildings, but also in industrial applications. “You can electrify more end-uses than you think and for those cases actually reduce the energy consumption compared to current levels,” explains Silvia Madeddu, co-author and also researcher at the Potsdam Institute.

“Take steel production: Electrifying the melting of recycled steel, the so called secondary steel, reduces the total process energy required and lowers the carbon intensity per tonne of steel produced,” says Madeddu. “All in all, we find that more than half of all energy demand from industry can be electrified by 2050.”

However, some bottlenecks to electrification do remain, the researchers point out. Slowest in the race to decarbonisation are long-haul aviation, shipping, and chemical feedstocks, i.e. fossil fuels used as raw materials in chemicals production.

The scale of the technological progress holds great opportunities for countries to leapfrog and for investors alike. However, not every technology is a success story so far. “In this study, we constrained the reliance on technologies which aim at taking carbon out of the atmosphere, simply because they have proven to be more difficult to scale than previously anticipated: Carbon Capture and Storage has not seen the sharp fall in costs that, say, solar power has. Biomass, in turn, crucially competes with food production for land use,” Luderer lays out. “Interestingly, we found that the accelerated electrification of energy demands can more than compensate for a shortfall of biomass and CCS, still keeping the 1.5 °C goal within reach while reducing land requirements for energy crops by two thirds.”

Gross residual fossil emissions and carbon dioxide removal.

“The era of electricity will come either way. But only sweeping regulation of fossil fuels across sectors and world regions — most importantly some form of carbon pricing — can ensure it happens in due time to reach 1.5 degrees,” Luderer says. Indeed, the simulations show that even if no climate policy at all is enacted, electricity will double in share over the course of the century. Yet in order to meet the goals of the Paris Agreement of limiting global warming to well below two degrees, decisive and global political coordination is crucial: pricing carbon, scrapping levies on electricity, expanding grid infrastructure, and redesigning electricity markets to reward storage and flexible demands. Here, hydrogen will be a crucial chain link, as it can flexibly convert renewable electricity into green fuels for sectors that cannot be electrified directly. “If these elements come together, the prospects of a renewables-based green energy future look truly electrifying,” says Luderer.

Nanoscale chemical heterogeneity dominates the optoelectronic response of alloyed perovskite solar cells

by Kyle Frohna, Miguel Anaya, Stuart Macpherson, Jooyoung Sung, Tiarnan A. S. Doherty, Yu-Hsien Chiang, Andrew J. Winchester, Kieran W. P. Orr, Julia E. Parker, Paul D. Quinn, Keshav M. Dani, Akshay Rao, Samuel D. Stranks in Nature Nanotechnology

Researchers from the University of Cambridge have used a suite of correlative, multimodal microscopy methods to visualise, for the first time, why perovskite materials are seemingly so tolerant of defects in their structure.

The most commonly used material for producing solar panels is crystalline silicon, but to achieve efficient energy conversion requires an energy-intensive and time-consuming production process to create the highly ordered wafer structure required.

Hyperspectral microscopy of perovskite solar cell device stacks.

In the last decade, perovskite materials have emerged as promising alternatives. The lead salts used to make them are much more abundant and cheaper to produce than crystalline silicon, and they can be prepared in a liquid ink that is simply printed to produce a film of the material. They also show great potential for other optoelectronic applications, such as energy efficient light emitting diodes (LEDs) and X-ray detectors.

The impressive performance of perovskites is surprising. The typical model for an excellent semiconductor is a very ordered structure, but the array of different chemical elements combined in perovskites creates a much ‘messier’ landscape. This heterogeneity causes defects in the material that lead to nanoscale ‘traps’, which reduce the photovoltaic performance of the devices. But despite the presence of these defects, perovskite materials still show efficiency levels comparable to their silicon alternatives.

Correlation between optoelectronic properties in FA0.79MA0.16Cs0.05Pb(I0.83Br0.17)3 perovskite films.

In fact, earlier research by the group has shown the disordered structure can actually increase the performance of perovskite optoelectronics, and their latest work seeks to explain why.

Combining a series of new microscopy techniques, the group present a complete picture of the nanoscale chemical, structural and optoelectronic landscape of these materials, that reveals the complex interactions between these competing factors and ultimately, shows which comes out on top.

“What we see is that we have two forms of disorder happening in parallel,” explains PhD student Kyle Frohna, “the electronic disorder associated with the defects that reduce performance, and then the spatial chemical disorder that seems to improve it. “And what we’ve found is that the chemical disorder — the ‘good’ disorder in this case — mitigates the ‘bad’ disorder from the defects by funnelling the charge carriers away from these traps that they might otherwise get caught in.”

In collaboration with Cambridge’s Cavendish Laboratory, the Diamond Light Source synchrotron facility in Didcot and the Okinawa Institute of Science and Technology in Japan, the researchers used several different microscopic techniques to look at the same regions in the perovskite film. They could then compare the results from all these methods to present the full picture of what’s happening at a nanoscale level in these promising new materials.

Spatial relationships between halide composition, structural and optoelectronic variations in FA0.79MA0.16Cs0.05Pb(I0.83Br0.17)3 perovskite films.

“The idea is we do something called multimodal microscopy, which is a very fancy way of saying that we look at the same area of the sample with multiple different microscopes and basically try to correlate properties that we pull out of one with the properties we pull out of another one,” says Frohna. “These experiments are time consuming and resource intensive, but the rewards you get in terms of the information you can pull out are excellent.”

The findings will allow the group and others in the field to further refine how perovskite solar cells are made in order to maximise efficiency.

“For a long time, people have thrown the term defect tolerance around, but this is the first time that anyone has properly visualised it to get a handle on what it actually means to be defect tolerant in these materials. “Knowing that these two competing disorders are playing off each other, we can think about how we effectively modulate one to mitigate the effects of the other in the most beneficial way.”

“In terms of the novelty of the experimental approach, we have followed a correlative multimodal microscopy strategy, but not only that, each standalone technique is cutting edge by itself,” says Miguel Anaya, Royal Academy of Engineering Research Fellow at Cambridge’s Department of Chemical Engineering and Biotechnology

“We have visualised and given reasons why we can call these materials defect tolerant. This methodology enables new routes to optimise them at the nanoscale to, ultimately, perform better for a targeted application. Now, we can look at other types of perovskites that are not only good for solar cells but also for LEDs or detectors and understand their working principles. “Even more importantly, the set of acquisition tools that we have developed in this work can be extended to study any other optoelectronic material, something that may be of great interest to the broader materials science community.”

“Through these visualisations, we now much better understand the nanoscale landscape in these fascinating semiconductors — the good, the bad and the ugly,” says Sam Stranks, University Assistant Professor in Energy at Cambridge’s Department of Chemical Engineering and Biotechnology.

“These results explain how the empirical optimisation of these materials by the field has driven these mixed composition perovskites to such high performances. But it has also revealed blueprints for design of new semiconductors that may have similar attributes — where disorder can be exploited to tailor performance.”

Quantifying Energy and Greenhouse Gas Emissions Embodied in Global Primary Plastic Trade Network

by Joseph Zappitelli, Elijah Smith, Kevin Padgett, Melissa M. Bilec, Callie W. Babbitt, Vikas Khanna in ACS Sustainable Chemistry & Engineering

In 1950, 2 million metric tonnes of new plastic was produced globally. In 2018, the world produced 360 million metric tonnes of plastics. Because of their low cost, durability and versatility, plastics are everywhere-including in the environment-and only 9 percent of the plastic ever generated has been recycled. The vast majority ends up in landfills, where its slow degradation allows it to accumulate, while pervasive microplastics have been found everywhere, from inside living bodies to the bottom of the ocean.

“At our current rate of plastic waste generation, increasing waste management capacity will not be sufficient to reach plastic pollution goals alone,” said Vikas Khanna, associate professor of civil and environmental engineering at the University of Pittsburgh Swanson School of Engineering. “There is an urgent need to take actions like limiting global virgin plastic production from fossil fuels and designing products and packaging for recyclability.”

New research led by Khanna gives a bird’s-eye view of the scale of plastic creation globally, tracing where it’s produced, where it ends up, and its environmental impact. The researchers found the greenhouse gas emissions associated with the production of plastic in 2018 staggering: 170 million metric tonnes of primary plastics were traded globally in 2018, with associated greenhouse gas emissions accounting for 350 million metric tonnes of CO2 equivalent-about the same amount produced by nations like Italy and France in a year.

“And if anything, our estimation is on the lower end. Converting primary plastic resins into end use products will result in additional greenhouse gases and other emissions,” warned Khanna.

“We know plastics are a problem, and we know keeping materials in a circular economy instead of the take-make-waste model we’re used to is a great solution,” said Khanna. “But if we don’t have an understanding of the current state of the system, then it’s hard to put numbers to it and understand the scale. We wanted to understand how plastics are mobilized across geographical boundaries.”

Since international trade plays such a critical role in making material goods available, including plastics, the researchers applied network theory to data from the UN Comtrade Database to understand the role of individual countries, trade relationships between countries, and structural characteristics that governed these interactions. The global primary plastic trade network (GPPTN) that they created designated each country as a “node” in the network and a trade relationship between two countries as an “edge,” allowing them to determine the critical actors (countries) and who is making the biggest impact.

The researchers examined 11 primary thermoplastic resins that make up the majority of plastic products. They found that a majority of the most influential nodes in the model are exporting more plastics than they import: Saudi Arabia is the leading exporter, followed by the U.S., South Korea, Germany and Belgium.The top five importers of primary plastic resins are China, Germany, the U.S., Italy and India.

Circos figure depicting embodied GHGs in the GPPTN for 2018.

In addition to the greenhouse gas emissions, the energy expended in the GPPTN is estimated to be the equivalent of 1.5 trillion barrels of crude oil, 230 billion cubic meters of natural gas, or 407 metric tonnes of coal. The carbon embedded in the model is estimated to be the carbon equivalent of 118 million metric tonnes of natural gas or 109 million metric tonnes of petroleum.

“The results are particularly important and timely, especially in light of the recent discussions during Conference of the Parties (COP26) in Glasgow and the importance of understanding where emissions are coming from in key sectors,” said co-author Melissa Bilec, Co-director of Mascaro Center for Sustainable Innovation and William Kepler Whiteford Professor of Civil and Environmental Engineering. “The collaboration with Dr. Khanna and his lab allows us to learn new systems-level modeling techniques as we converge towards understanding solutions to our complex challenges.”

Using more recycled plastics instead of creating new resins that eventually make their way to landfills would be substantially better for the environment; however, financial and behavioral barriers both need to be addressed before a true circular economy for plastics can become a reality.

Serpentinite-derived slab fluids control the oxidation state of the subarc mantle

by Yuxiang Zhang, Esteban Gazel, Glenn A. Gaetani, Frieder Klein in Science Advances

A new study co-led by a Cornell researcher has identified serpentinite — a green rock that looks a bit like snakeskin and holds fluids in its mineral structures — as a key driver of the oxygen recycling process, which helped create and maintain the sustaining atmosphere for life on Earth.

“This cycle is a really a big deal,” said Esteban Gazel, associate professor of earth and atmospheric sciences in Cornell’s College of Engineering, and co-lead author on the study. “In the end, we’re talking about the budget of oxygen on the planet and how that gets balanced through processes like subduction.”

Earth is constantly recycling its life-giving supply of water and oxygen as tectonic plates sink, or subduct, deep into the planet. Elements are carried down as one piece of the planet’s crust slips below another, and resurface through the resulting volcanoes. It’s a critical process, but how, exactly, subduction recycles oxygen and allows it to interact with other elements has always been a topic of debate among geoscientists.

Plots of Cu versus MgO for volcanic rocks from arcs and mid-ocean ridges.

The new finding changes how geoscientists understand the underlying process of Earth’s geochemical cycle. The reason geoscientists had, until now, failed to make this discovery was because of something the COVID-19 pandemic had provided Gazel — time to look at massive amounts of data.

Using volcanoes to probe the deep Earth, past studies have examined oxygen levels in the Earth’s mantle — the magma-filled layer directly under the crust — for clues. Some geoscientists have pointed to increased oxidation below volcanic arcs, where the hydrated oceanic lithosphere sinks into the mantle. A leading theory had been that ocean water delivering hydrogen into the mantle was influencing its oxidation state, but the new study found that oxygen is entering the mantle in fluids derived from “heated and pressurized” serpentinite rocks.

Below the sea floor, the process of serpentinization creates rocks that trap highly oxidizing fluids inside, and these serpentinites eventually get subducted back into the mantle.

“Eventually, those serpentinite juices are going to be squeezed from the slab,” said Gazel, who is also a faculty fellow at the Cornell Atkinson Center for Sustainability. “Depending on the angle and the thermal conditions of the subducting slab, those fluids are released and they oxidize the mantle below volcanoes.”

Sketch of serpentinite subduction.

With travel restrictions and his laboratory under construction, Gazel and his colleague Yuxiang Zhang from the Institute of Oceanology, Chinese Academy of Sciences spent time in 2020 carefully analyzing every existing dataset for single arcs and their lava compositions. Adding to the analysis were serpentinization expert Frieder Klein and chemical thermodynamics expert Glenn Gaetani, both scientists from the Woods Hole Oceanographic Institution.

“We were looking at the correlation with different processes,” Gazel said. “For instance, there were some regional datasets that correlated the thickness of the crust with oxidation, but it just didn’t make sense once we made our study global.”

Once enough datasets had been combined, certain correlations were eliminated while the correlation between serpentinization related fluids and oxidization became evident. Specifically, the subduction system’s thermodynamic conditions and geometry proved to control the dehydration of serpentine and the oxidation state of the mantle, with steeper, colder subduction zones providing more oxidization.

Improving Pd–N–C fuel cell electrocatalysts through fluorination-driven rearrangements of local coordination environment

by Jinfa Chang, Guanzhi Wang, Maoyu Wang, Qi Wang, Boyang Li, Hua Zhou, Yuanmin Zhu, Wei Zhang, Mahmoud Omer, Nina Orlovskaya, Qing Ma, Meng Gu, Zhenxing Feng, Guofeng Wang, Yang Yang in Nature Energy

Alternative-energy research at Oregon State University is charting a path toward the mass adoption of clean cars powered by direct-ethanol fuel cells.

Zhenxing Feng of the OSU College of Engineering helped lead the development of a catalyst that solves three key problems long associated with DEFC, as the cells are known: low efficiency, the cost of catalytic materials and the toxicity of chemical reactions inside the cells.

Schematic illustration of the fluorination-driven rearrangement of the LCE.

Feng and collaborators at Oregon State, the University of Central Florida and the University of Pittsburgh found that putting fluorine atoms into palladium-nitrogen-carbon catalysts had a number of positive effects — including keeping the power-dense cells stable for nearly 6,000 hours. A catalyst is a substance that increases the rate of a reaction without itself undergoing any permanent chemical change.

Cars and trucks powered by gasoline or diesel engines rely on the combustion of fossil fuels, which results in emissions of the greenhouse gas carbon dioxide. Motor vehicles are one of the main sources of atmospheric CO2, a primary factor in climate change.

“Combustion engines produce enormous amounts of carbon dioxide,” said Feng, associate professor of chemical engineering. “To achieve carbon-neutral and zero-carbon-emissions goals, alternative energy conversion devices using the fuel from renewable and sustainable sources are urgently needed. Direct-ethanol fuel cells can potentially replace gasoline- and diesel-based energy conversion systems as power sources.”

Morphology and atomic structure of Pd/X–F catalysts.

Feng and collaborators are in the process of soliciting funding to develop prototypes of DEFC units for portable devices and vehicles.

“If this is successful, we can deliver a device for commercialization in five years,” he said. “With more industrial collaborators, the DEFC vehicle can be implemented in 10 years, hopefully.”

Ethanol, also known as ethyl alcohol, consists of carbon, hydrogen and oxygen — its chemical formula is C2H6O — and is the active ingredient in alcoholic drinks. It occurs naturally through the fermentation of sugars by yeasts and can be derived from many sources including corn, wheat, grain sorghum, barley, sugar cane and sweet sorghum. Most of the ethanol produced in the United States is made in the Midwest, most typically from corn.

A fuel cell, Feng explains, relies on the chemical energy of hydrogen or other fuels to cleanly and efficiently produce electricity. They can use a wide range of fuels and feedstocks and can serve systems as large as a utility power plant and as small as a laptop computer.

“In DEFC technology, ethanol can be generated from a number of sources, particularly biomass like sugar cane, wheat and corn,” Feng said. “The benefit of using biological sources to produce ethanol is that plants absorb atmospheric carbon dioxide.”

A liquid and thus easily stored and transported, ethanol can deliver more energy per kilogram than other fuels like methanol or pure hydrogen. Plus, Feng points out, infrastructure is already in place for both producing and distributing ethanol, making DEFC an attractive option for replacing internal combustion engines.

DFT calculations.

“The first vehicle powered by an ethanol-based fuel cell was developed in 2007,” Feng said. “However, the further development of DEFC vehicles has significantly lagged due to the low efficiency of DEFC, the costs related to catalysts and the risk of catalyst poisoning from carbon monoxide produced in reactions inside the fuel cell.”

To tackle those problems the research team, which also included OSU’s Maoyu Wang and scientists from Southern University of Science and Technology in China and Argonne National Laboratory, developed high-performance palladium alloy catalysts that use less of the precious metal than current palladium-based catalysts. Palladium, platinum and ruthenium are elements valued for their catalytic properties but expensive and difficult to obtain.

“Our team showed that introducing fluorine atoms into palladium-nitrogen-carbon catalysts modifies the environment around the palladium, and that improves both activity and durability for two important reactions in the cell: the ethanol oxidation reaction and the oxygen reduction reaction,” Feng said. “Advanced synchrotron X-ray spectroscopy characterizations made at Argonne suggest that fluorine atom introduction creates a more nitrogen-rich palladium surface, which is favorable for catalysis. Durability is enhanced by inhibiting palladium migration and decreasing carbon corrosion.”

External electric field promotes ammonia stripping from wastewater

by Young-Chae Song, Jung-Hui Woo, Gyung-Geun Oh, Dong-Hoon Kim, Chae-Young Lee, Hyun-Woo Kim in Water Research

Given its environmental toxicity, ammonia is removed during wastewater purification and then used for fertilizers or fuel. However, this process is very energy and chemical intensive. Now, researchers have shown that the application of an external electric field can greatly enhance the efficiency of ammonia removal from wastewater, making it more energy- and cost-effective.

Ammonia is one of many pollutants present in wastewater and can be toxic for marine and terrestrial life. Therefore, in a process called air stripping, it is removed from wastewater and later used as a fertilizer or fuel. Air stripping converts ammonia into a gas, that can then escape the wastewater from its surface. But this process is not efficient: it is energy-intensive, and requires specific temperatures, air supply, and a lot of chemicals, making it expensive.

Addressing these drawbacks, researchers from South Korea have demonstrated that the simple application of an electric field during air stripping can substantially improve the efficiency of ammonia removal, even under sub-optimal conditions. “So far, the removal of ammonia from wastewater was thought to be dependent on only pH, temperature, and air supply. However, we have shown that an electrical field can also act as a modulator of this process,” says Prof. Young-Chae Song, the lead investigator on this study.

Prof. Song and his team used a combination of live experiments with an ammonia stripping tank and deep learning to understand how electric fields of different strengths influence the efficiency of ammonia removal from wastewater. They found that electric fields with an alternating current of 50 MHz and a power of 15 V/cm significantly improves the ammonia removal efficiency, increasing it from 51% to 94%, even under sub-optimal conditions. Therefore, improved ammonia yields could be achieved while considerably reducing the consumption of energy and chemicals.

Prof. Song comments, “Our simulations showed that electric field application provides a similar efficiency of ammonia removal to conventional methods at a much lower temperature, air supply, and pH. Moreover, the energy needed to power the electric field is a minute fraction of the energy required to achieve these ‘optimal’ conditions.”

Indeed, this new electric field-coupled platform could provide a more economical way of stripping ammonia from wastewater and reducing the carbon footprint associated with this process.


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