After 40 Years of Searching, Scientists Identify The Key Flaw in Solar Panel Efficiency

Solar panels are fantastic pieces of technology, but we need to work out how to make them even more efficient – and scientists just solved a 40-year-old mystery around one of the key obstacles to increased efficiency.

A new study outlines a material defect in silicon used to produce solar cells that has previously gone undetected. It could be responsible for the 2 percent efficiency drop that solar cells can see in the first hours of use: Light Induced Degradation (LID).

Multiplied by the increasing number of panels installed at solar farms around the world, that drop equals a significant cost in gigawatts that non-renewable energy sources have to make up for.

New Efficient Solar Panels Coming to the Market in 2019

In fact, the estimated loss in efficiency worldwide from LID is estimated to equate to more energy than can be generated by the UK’s 15 nuclear power plants. The new discovery could help scientists make up some of that shortfall.

“Because of the environmental and financial impact solar panel ‘efficiency degradation’ has been the topic of much scientific and engineering interest in the last four decades,” says one of the researchers, Tony Peaker from the University of Manchester in the UK.

“However, despite some of the best minds in the business working on it, the problem has steadfastly resisted resolution until now.”

To find what 270 research papers across four decades had previously been unable to determine, the latest study used an electrical and optical technique called deep-level transient spectroscopy (DLTS) to find weaknesses in the silicon.

Here’s what the DLTS analysis found: As the electronic charge in the solar cells gets transformed into sunlight, the flow of electrons gets trapped; in turn, that reduces the level of electrical power that can be produced.

This defect lies dormant until the solar panel gets heated, the team found.

“We’ve proved the defect exists, its now an engineering fix that is needed,” says one of the researchers, Iain Crowe from the University of Manchester.

The researchers also found that higher quality silicon had charge carriers (electrons which carry the photon energy) with a longer ‘lifetime’, which backs up the idea that these traps are linked to the efficiency degradation.

What’s more, heating the material in the dark, a process often used to remove traps from silicon, seems to reverse the degradation.

The work to push solar panel efficiency rates higher continues, with breakthroughs continuing to happen in the lab, and nature offering up plenty of efficiency tipsas well. Now that the Light Induced Degradation mystery has been solved, solar farms across the globe should benefit.

“An absolute drop of 2 percent in efficiency may not seem like a big deal, but when you consider that these solar panels are now responsible for delivering a large and exponentially growing fraction of the world’s total energy needs, it’s a significant loss of electricity generating capacity,” says Peaker.

The research has been published in the Journal of Applied Physics.

University of Manchester – How Can Graphene Help Desalination?(Video+)

Researchers at The University of Manchester’s National Graphene Institute in the UK have succeeded in making artificial channels just one atom in size for the first time. The new capillaries, which are very much like natural protein channels such as aquaporins, are small enough to block the flow of smallest ions like Na+ and Cl- but allow water to flow through freely. As well as improving our fundamental understanding of molecular transport at the atomic scale, and especially in biological systems, the structures could be ideal in desalination and filtration technologies.

 

 

Read More from the University of Manchester

Like …. Scientists develop a new method to revolutionise graphene printed electronics

U of Manchester – Nobel-prize Winning Chemistry for Clean Energy Breakthrough used to Reduce the cost of Fuel Cells used in Renewable Energy Vehicles – Reduce harmful emissions from ICE’s

Credit: CC0 Public Domain

Scientists have used a Nobel-prize winning chemistry technique on a mixture of metals to potentially reduce the cost of fuel cells used in electric cars and reduce harmful emissions from conventional vehicles.

The researchers have translated a biological technique, which won the 2017 Nobel Chemistry Prize, to reveal atomic scale chemistry in metal nanoparticles. These materials are one of the most effective catalysts for energy converting systems such as fuel cells. It is the first time this technique has been for this kind of research.

The particles have a complex star-shaped geometry and this new work shows that the edges and corners can have different chemistries which can now be tuned to reduce the cost of batteries and catalytic convertors.

The 2017 Nobel Prize in Chemistry was awarded to Joachim Frank, Richard Henderson and Jacques Dubochet for their role in pioneering the technique of single particle reconstruction. This electron microscopy technique has revealed the structures of a huge number of viruses and proteins but is not usually used for metals.

Now, a team at the University of Manchester, in collaboration with researchers at the University of Oxford and Macquarie University, have built upon the Nobel Prize winning technique to produce three dimensional elemental maps of metallic nanoparticles consisting of just a few thousand atoms.

Published in the journal Nano Letters, their research demonstrates that it is possible to map different elements at the nanometre scale in three dimensions, circumventing damage to the particles being studied.

Metal nanoparticles are the primary component in many catalysts, such as those used to convert toxic gases in car exhausts. Their effectiveness is highly dependent on their structure and chemistry, but because of their incredibly small structure, electron microscopes are required in order to provide image them. However, most imaging is limited to 2-D projections.

“We have been investigating the use of tomography in the electron microscope to map elemental distributions in three dimensions for some time,” said Professor Sarah Haigh, from the School of Materials, University of Manchester. “We usually rotate the particle and take images from all directions, like a CT scan in a hospital, but these particles were damaging too quickly to enable a 3-D image to be built up. Biologists use a different approach for 3-D imaging and we decided to explore whether this could be used together with spectroscopic techniques to map the different elements inside the nanoparticles.”

“Like ‘single particle reconstruction’ the technique works by imaging many particles and assuming that they are all identical in structure, but arranged at different orientations relative to the electron beam. The images are then fed in to a computer algorithm which outputs a three dimensional reconstruction.”

In the present study the new 3-D chemical imaging method has been used to investigate platinum-nickel (Pt-Ni) metal nanoparticles.

Lead author, Yi-Chi Wang, also from the School of Materials, added: “Platinum based nanoparticles are one of the most effective and widely used catalytic materials in applications such as fuel cells and batteries. Our new insights about the 3-D local chemical distribution could help researchers to design better catalysts that are low-cost and high-efficiency.”

“We are aiming to automate our 3-D chemical reconstruction workflow in the future”, added author Dr. Thomas Slater.”We hope it can provide a fast and reliable method of imaging nanoparticle populations which is urgently needed to speed up optimisation of nanoparticle synthesis for wide ranging applications including biomedical sensing, light emitting diodes, and solar cells.”

 Explore further: Video: The 2017 Nobel Prize in Chemistry: Cryo-electron microscopy explained

More information: Yi-Chi Wang et al. Imaging Three-Dimensional Elemental Inhomogeneity in Pt–Ni Nanoparticles Using Spectroscopic Single Particle Reconstruction, Nano Letters (2019). DOI: 10.1021/acs.nanolett.8b03768

Journal reference: Nano Letters  

Provided by: University of Manchester

 

Atomic-scale capillaries block smallest ions thanks to Graphene – Structures are ideal in Desalination and Filtration Technologies

                                       Credit: University of Manchester

 

** See More About Graphene (YouTube Video) and Desalination at the end of this article **

Researchers at The University of Manchester’s National Graphene Institute in the UK have succeeded in making artificial channels just one atom in size for the first time. The new capillaries, which are very much like natural protein channels such as aquaporins, are small enough to block the flow of smallest ions like Na+ and Cl- but allow water to flow through freely. As well as improving our fundamental understanding of molecular transport at the atomic scale, and especially in biological systems, the structures could be ideal in desalination and filtration technologies.

“Obviously, it is impossible to make capillaries smaller than one atom in size,” explains team leader Sir Andre Geim. “Our feat seemed nigh on impossible, even in hindsight, and it was difficult to imagine such tiny capillaries just a couple of years ago.”

Naturally occurring protein channels, such as aquaporins, allow water to quickly permeate through them but block hydrated ions larger than around 7 A in size thanks to mechanisms like steric (size) exclusion and electrostatic repulsion. Researchers have been trying to make artificial capillaries that work just like their natural counterparts, but despite much progress in creating nanoscale pores and nanotubes, all such structures to date have still been much bigger than biological channels.

Geim and colleagues have now fabricated channels that are around just 3.4 A in height. This is about half the size of the smallest hydrated ions, such as K+ and Cl-, which have a diameter of 6.6 A. These channels behave just like protein channels in that they are small enough to block these ions but are sufficiently big to allow water molecules (with a diameter of around 2.8 A) to freely flow through.

The structures could, importantly, help in the development of cost-effective, high-flux filters for water desalination and related technologies – a holy grail for researchers in the field.

Credit: University of Manchester

Atomic-scale Lego

Publishing their findings in Science the researchers made their structures using a van der Waals assembly technique, also known as “atomic-scale Lego”, which was invented thanks to research on graphene. “We cleave atomically flat nanocrystals just 50 and 200 nanometre in thickness from bulk graphite and then place strips of monolayer graphene onto the surface of these nanocrystals,” explains Dr. Radha Boya, a co-author of the research paper. “These strips serve as spacers between the two crystals when a similar atomically-flat crystal is subsequently placed on top. The resulting trilayer assembly can be viewed as a pair of edge dislocations connected with a flat void in between. This space can accommodate only one atomic layer of water.”

Using the graphene monolayers as spacers is a first and this is what makes the new channels different from any previous structures, she says.

The Manchester scientists designed their 2-D capillaries to be 130 nm wide and several microns in length. They assembled them atop a silicon nitride membrane that separated two isolated containers to ensure that the channels were the only pathway through which water and ions could flow.

Until now, researchers had only been able to measure water flowing though capillaries that had much thicker spacers (around 6.7 A high). And while some of their molecular dynamics simulations indicated that smaller 2-D cavities should collapse because of van der Waals attraction between the opposite walls, other calculations pointed to the fact that water molecules inside the slits could actually act as a support and prevent even one-atom-high slits (just 3.4 A tall) from falling down. This is indeed what the Manchester team has now found in its experiments.

Measuring water and ion flow

“We measured water permeation through our channels using a technique known as gravimetry,” says Radha. “Here, we allow water in a small sealed container to evaporate exclusively through the capillaries and we then accurately measure (to microgram precision) how much weight the container loses over a period of several hours.”

To do this, the researchers say they built a large number of channels (over a hundred) in parallel to increase the sensitivity of their measurements. They also used thicker top crystals to prevent sagging, and clipped the top opening of the capillaries (using plasma etching) to remove any potential blockages by thin edges present here.

To measure ion flow, they forced ions to move through the capillaries by applying an electric field and then measured the resulting currents. “If our capillaries were two atoms high, we found that small ions can move freely though them, just like what happens in bulk water,” says Radha. “In contrast, no ions could pass through our ultimately-small one-atom-high channels.

“The exception was protons, which are known to move through water as true subatomic particles, rather than ions dressed up in relatively large hydration shells several angstroms in diameter. Our channels thus block all hydrated ions but allow protons to pass.”

Since these capillaries behave in the same way as protein channels, they will be important for better understanding how water and ions behave on the molecular scale – as in angstrom-scale biological filters. “Our work (both present and previous) shows that atomically-confined water has very different properties from those of bulk water,” explains Geim. “For example, it becomes strongly layered, has a different structure, and exhibits radically dissimilar dielectric properties.”

 Explore further: Devices made from 2-D materials separate salts in seawater

More information: Dorri Halbertal et al. Imaging resonant dissipation from individual atomic defects in graphene, Science (2017). DOI: 10.1126/science.aan0877 , https://arxiv.org/abs/1811.09227

Journal reference: Science  

Provided by: University of Manchester

Want to Read More About Cutting Edge Desalination, Energy Storage and Carbon Nanotubes?

MIT: Optimizing carbon nanotube electrodes for energy storage and water desalination applications

 

 

 

Graphene for Water Desalination

 

Water, one of the world’s most abundant and highly demanded resources for sustaining life, agriculture, and industry, is being contaminated globally or is unsafe for drinking, creating a need for new and better desalination methods. Current desalination methods have high financial, energy, construction, and operating costs, resulting in them contributing to less than 1% of the world’s reserve water supplies. Advances in nanoscale science and engineering suggest that more cost effective and environmentally friendly desalination process using graphene is possible …

Scientists at the University of Manchester develop revolutionary method for graphene printed electronics – Impact for IoT

This visualisation shows layers of graphene used for membranes. Credit: University of Manchester

 

A team of researchers based at The University of Manchester have found a low cost method for producing graphene printed electronics, which significantly speeds up and reduces the cost of conductive graphene inks.

Printed electronics offer a breakthrough in the penetration of information technology into everyday life. The possibility of printing electronic circuits will further promote the spread of Internet of Things (IoT) applications.

The development of printed conductive inks for electronic applications has grown rapidly, widening applications in transistors, sensors, antennas RFID tags and wearable electronics.

Current conductive inks traditionally use metal nanoparticles for their high electrical conductivity. However, these materials can be expensive or easily oxidised, making them far from ideal for low cost IoT applications.

The team have found that using a material called dihydro-levo-gucosenone known as Cyrene is not only non-toxic but is environmentally- friendly and sustainable but can also provide higher concentrations and conductivity of graphene ink.

Professor Zhiurn Hu said: “This work demonstrates that printed graphene technology can be low cost, sustainable, and environmentally friendly for ubiquitous wireless connectivity in IoT era as well as provide RF energy harvesting for low power electronics”.

Professor Sir Kostya Novoselov said: “Graphene is swiftly moving from research to application domain. Development of production methods relevant to the end-user in terms of their flexibility, cost and compatibility with existing technologies are extremely important. This work will ensure that implementation of graphene into day-to-day products and technologies will be even faster”.

Kewen Pan, the lead author on the paper said: “This perhaps is a significant step towards commercialisation of printed graphene technology. I believe it would be an evolution in printed electronics industry because the material is such low cost, stable and environmental friendly”.

The National Physical Laboratory (NPL), who were involved in measurements for this work, have partnered with the National Graphene Institute at The University of Manchester to provide a materials characterisation service to provide the missing link for the industrialisation of graphene and 2-D materials. They have also published a joint NPL and NGI a good practice guide which aims to tackle the ambiguity surrounding how to measure graphene’s characteristics.

Professor Ling Hao said: “Materials characterisation is crucial to be able to ensure performance reproducibility and scale up for commercial applications of graphene and 2-D materials. The results of this collaboration between the University and NPL is mutually beneficial, as well as providing measurement training for Ph.D. students in a metrology institute environment.”

Graphene has the potential to create the next generation of electronics currently limited to science fiction: faster transistors, semiconductors, bendable phones and flexible wearable electronics.

 Explore further: Fully integrated circuits printed directly onto fabric

Provided by: University of Manchester

 

Nanoscale blood test technique could lead to accelerated early diagnosis and personalized medicines

A technique to get more information from the blood of cancer patients than previously possible has been developed.

“We hope this technique could be a springboard for further research, from monitoring disease progression or recurrence, to identifying which treatment is best for each patient and potentially finding new biomarkers for early diagnosis.”- Professor Kostas Kostarelos

The discovery could potentially accelerate early diagnosis, speed up drug discovery and lead to advancements in personalised medicines.

The Cancer Research UK-funded study* is published in Advanced Materials today (Wednesday).

The scientists, from the University of Manchester, collected blood samples from women with advanced ovarian cancer who were treated with a type of chemotherapy called CAELYX®.

This chemotherapy drug is contained in a soft, lipid-based nanoparticle, called a liposome, which acts as a vessel to help minimise side effects**.

Women gave a sample of blood, following an injection of CAELYX® over a course of 90 minutes as part of their treatment. By extracting the injected liposomes, the scientists were able to detect a wide variety of biomolecules that stuck to the surface of the liposome – called the ‘biomolecule corona’.

Professor Kostas Kostarelos, lead author from the University of Manchester, said: “We’re astonished at how rich the information was on the surface of the liposomes taken from the blood. We hope this technique could be a springboard for further research, from monitoring disease progression or recurrence, to identifying which treatment is best for each patient and potentially finding new biomarkers for early diagnosis.”

This is a step forward in developing a better technique to gather information from patients’ blood – a ‘halo effect’ of biomolecules sticking to the liposomes has been seen before, but only after dipping the nanoparticles in blood samples in a tube outside the patient’s body.

Dr Marilena Hadjidemetriou, study author from the University of Manchester, said: “The blood is a potential goldmine of information, but there’s a challenge to amplify cancer signals that would otherwise be buried within the ‘noise’.

“More abundant proteins mask rarer and smaller molecules that could be significant in helping us to understand disease progression or finding potential new drug targets. This technique overcomes this challenge.”

Professor Caroline Dive, Cancer Research UK’s expert in liquid biopsies, said: “Finding a test to help diagnose, track and treat cancer is something many scientists are pursuing. Liquid biopsies are quicker, cheaper and less invasive than many other tests, and this technique is an important early step in developing such a test. Further work will reveal what the information captured using liposomes can tell us about the disease.”

The researchers now hope to use this technique in mice to help find the best patterns of biomarkers to identify cancers in the early stages of disease as part of their Cancer Research UK Pioneer Award, which funds innovative ideas from any discipline that could revolutionise our understanding of cancer.

Source

Graphene water filter turns whisky clear – How Can Graphene Help Desalination? +Video

Credit: University of Manchester

Previously graphene-oxide membranes were shown to be completely impermeable to all solvents except for water. However, a study published in Nature Materials, now shows that we can tailor the molecules that pass through these membranes by simply making them ultrathin.

The research team led by Professor Rahul Nair at the National Graphene Institute and School of Chemical Engineering and Analytical Science at The University of Manchester tailored this membrane to allow all solvents to pass through but without compromising it’s ability to sieve out the smallest of particles.

In the newly developed ultrathin membranes, graphene-oxide sheets are assembled in such a way that pinholes formed during the assembly are interconnected by graphene nanochannels, which produces an atomic-scale sieve allowing the large flow of solvents through the membrane.

This new research allows for expansion in the applications of graphene based membranes from sea water desalination to organic solvent nanofiltration (OSN). Unlike sea water desalination, which separate salts from water, OSN technology separates charged or uncharged organic compounds from an organic solvent.

As an example, Manchester scientists demonstrated that graphene-oxide membranes can be designed to completely remove various organic dyes as small as a nanometre dissolved in methanol.

Credit: University of Manchester

Prof. Nair said, “Just for a fun, we even filtered whisky and cognac through the graphene-oxide membrane. The membrane allowed the alcohol to pass through but removed the larger molecules, which gives the amber colour. The clear whisky smells similar to the original whisky but we are not allowed to drink it in the lab, however it was a funny Friday night experiment!”

The newly developed membranes not only filter out small molecules but it boosts the filtration efficiency by increasing the solvent flow rate.

Prof. Nair added “Chemical separation is all about energy, various chemical separation processes consume about half of industrial energy useage. Any new efficient separation process will minimize the consumption of energy, which is in high demand now. By 2030, the world is projected to consume 60% more energy than today.”

Dr. Su, who led the experiment added “The developed membranes are not only useful for filtering alcohol, but the precise sieve size and high flux open new opportunity to separate molecules from different organic solvents for chemical and pharmaceutical industries. This development is particularly important because most of the existing polymer-based membranes are unstable in organic solvents whereas the developed graphene-oxide membrane is highly stable.”

How Can Graphene Help Desalination?

 

Graphene-oxide membranes developed at the National Graphene Institute have attracted widespread attention for water filtration and desalination applications, providing a potential solution to the water scarcity.

By using ultra-thin membranes, this is the first clear-cut experiment to show how other solvents can be filtered out, proving that there is potential for organic solvent nanofiltration.

Graphene- the world’s first two-dimensional material is known for its versatile superlatives, it can be both hydrophobic and hydrophilic, stronger than steel, flexible, bendable and one million times thinner than a human hair.

This research has changed the perception of what graphene-oxide membranes are capable of and how we can use them. By being able to design these membranes to filter specific molecules or solvents, it opens up new potential uses that have previously not been explored.

 Explore further: Graphene sieve turns seawater into drinking water

More information: Q. Yang et al. Ultrathin graphene-based membrane with precise molecular sieving and ultrafast solvent permeation, Nature Materials (2017). DOI: 10.1038/nmat5025

Journal reference: Nature Materials  

Provided by: University of Manchester

 

Graphene Oxide Membrane (Sieve) Turns Seawater into Drinking Water: University of Manchester

Newsfacts:

New research shows graphene can filter common salts from water to make it safe to drink Findings could lead to affordable desalination technology

 Graphene membrane

Graphene-oxide membranes have attracted considerable attention as promising candidates for new filtration technologies. Now the much sought-after development of making membranes capable of sieving common salts has been achieved.

New research demonstrates the real-world potential of providing clean drinking water for millions of people who struggle to access adequate clean water sources.
The new findings from a group of scientists at The University of Manchester were published today in the journal Nature Nanotechnology.
Previously graphene-oxide membranes have shown exciting potential for gas separation and water filtration.

Graphene-oxide membranes developed at the National Graphene Institute have already demonstrated the potential of filtering out small nanoparticles, organic molecules, and even large salts. Until now, however, they couldn’t be used for sieving common salts used in desalination technologies, which require even smaller sieves.

Previous research at The University of Manchester found that if immersed in water, graphene-oxide membranes become slightly swollen and smaller salts flow through the membrane along with water, but larger ions or molecules are blocked.

The Manchester-based group have now further developed these graphene membranes and found a strategy to avoid the swelling of the membrane when exposed to water.
The pore size in the membrane can be precisely controlled which can sieve common salts out of salty water and make it safe to drink.
Realisation of scalable membranes with uniform pore size down to atomic scale is a significant step forward and will open new possibilities for improving the efficiency of desalination technology.

Professor Rahul Raveendran Nair

As the effects of climate change continue to reduce modern city’s water supplies, wealthy modern countries are also investing in desalination technologies. Following the severe floods in California major wealthy cities are also looking increasingly to alternative water solutions.

When the common salts are dissolved in water, they always form a ‘shell’ of water molecules around the salts molecules. This allows the tiny capillaries of the graphene-oxide membranes to block the salt from flowing along with the water. Water molecules are able to pass through the membrane barrier and flow anomalously fast which is ideal for application of these membranes for desalination.

Professor Rahul Nair, at The University of Manchester said: “Realisation of scalable membranes with uniform pore size down to atomic scale is a significant step forward and will open new possibilities for improving the efficiency of desalination technology.

“This is the first clear-cut experiment in this regime. We also demonstrate that there are realistic possibilities to scale up the described approach and mass produce graphene-based membranes with required sieve sizes.”

Mr. Jijo Abraham and Dr. Vasu Siddeswara Kalangi were the joint-lead authors on the research paper: “The developed membranes are not only useful for desalination, but the atomic scale tunability of the pore size also opens new opportunity to fabricate membranes with on-demand filtration capable of filtering out ions according to their sizes.” said Mr. Abraham.

By 2025 the UN expects that 14% of the world’s population will encounter water scarcity. This technology has the potential to revolutionise water filtration across the world, in particular in countries which cannot afford large scale desalination plants.

It is hoped that graphene-oxide membrane systems can be built on smaller scales making this technology accessible to countries which do not have the financial infrastructure to fund large plants without compromising the yield of fresh water produced.

Advanced materials

A UK-based team of researchers has created a graphene-based sieve capable of removing salt from seawater.
The sought-after development could aid the millions of people without ready access to clean drinking water. The promising graphene oxide sieve could be highly efficient at filtering salts, and will now be tested against existing desalination membranes.
It has previously been difficult to manufacture graphene-based barriers on an industrial scale. Reporting their results in the journal Nature Nanotechnology, scientists from the University of Manchester, led by Dr Rahul Nair, shows how they solved some of the challenges by using a chemical derivative called graphene oxide.
Advanced materials is one of The University of Manchester’s research beacons – examples of pioneering discoveries, interdisciplinary collaboration and cross-sector partnerships that are tackling some of the biggest questions facing the planet. #ResearchBeacons

 

A Holey Graphene Electrode framework that enables highly efficient charge delivery – Making Better Batteries for the Future

This visualisation shows layers of graphene used for membranes. Credit: University of Manchester

A team of researchers affiliated with institutions in the U.S., China and the Kingdom of Saudi Arabia has developed a new type of porous graphene electrode framework that is capable of highly efficient charge delivery. In their paper published in the journal Science, the group describes how they overcame traditional conflicts arising between trade-offs involving density and speed to produce an electrode capable of facilitating rapid ion transport. Hui-Ming Cheng and Feng Li with the Chinese Academy of Sciences offer a Perspective piece on the work done by the team in the same journal issue, and include some opinions of their own regarding where such work is likely heading.

In a perfect world, batteries would have unlimited energy storage delivered at speeds high enough to power devices with unlimited needs. The phaser from Star Trek, for example, would require far more power and speed than is possible in today’s devices.

While it is unlikely that such technology will ever come about, it does appear possible that batteries of the future will perform much better than today, likely due to nano-structured materials—they have already shown promise when used as electrode material due to their unique properties. Unfortunately, their use has been limited thus far due to the ultra-thin nature of the resulting electrodes and their extremely low mass loadings compared to those currently in use. In this new effort, the researchers report on a new way to create an electrode using graphene that overcomes such limitations.

The electrode they built is porous, which in this case means that it has holes in it. Those holes, as Cheng and Li note, allow better charge transport while also offering improved capacity retention density. The graphene framework they built, they note, offers a superior means of electron transport and its porous nature allows for a high ion diffusion rate—the holes force the ions to take shortcuts, reducing diffusion.

Cheng and Li suggest the new work is likely to inspire similar designs in the search for better electrode materials, which they further suggest appears likely to lead to new electrodes that are not only practical, but have high mass loadings.

Explore further: New graphene framework bridges gap between traditional capacitors, batteries

More information: Hongtao Sun et al. Three-dimensional holey-graphene/niobia composite architectures for ultrahigh-rate energy storage, Science (2017). DOI: 10.1126/science.aam5852

Abstract
Nanostructured materials have shown extraordinary promise for electrochemical energy storage but are usually limited to electrodes with rather low mass loading (~1 milligram per square centimeter) because of the increasing ion diffusion limitations in thicker electrodes.

We report the design of a three-dimensional (3D) holey-graphene/niobia (Nb2O5) composite for ultrahigh-rate energy storage at practical levels of mass loading (>10 milligrams per square centimeter). The highly interconnected graphene network in the 3D architecture provides excellent electron transport properties, and its hierarchical porous structure facilitates rapid ion transport.

By systematically tailoring the porosity in the holey graphene backbone, charge transport in the composite architecture is optimized to deliver high areal capacity and high-rate capability at high mass loading, which represents a critical step forward toward practical applications.

Journal reference: Science

 

Turning Seawater into Drinking Water ~ Graphene Sieves May Hold the Key

A graphene membrane. Credit: The University of Manchester

 

“By 2025 the UN expects that 14% of the world’s population will encounter water scarcity.”

Graphene-oxide membranes have attracted considerable attention as promising candidates for new filtration technologies. Now the much sought-after development of making membranes capable of sieving common salts has been achieved.

New research demonstrates the real-world potential of providing clean drinking water for millions of people who struggle to access adequate clean water sources.

The new findings from a group of scientists at The University of Manchester were published today in the journal Nature Nanotechnology. Previously graphene-oxide membranes have shown exciting potential for gas separation and water filtration.

Graphene-oxide membranes developed at the National Graphene Institute have already demonstrated the potential of filtering out small nanoparticles, organic molecules, and even large salts. Until now, however, they couldn’t be used for sieving common salts used in desalination technologies, which require even smaller sieves.

Previous research at The University of Manchester found that if immersed in water, graphene-oxide membranes become slightly swollen and smaller salts flow through the membrane along with water, but larger ions or molecules are blocked.

The Manchester-based group have now further developed these graphene membranes and found a strategy to avoid the swelling of the membrane when exposed to water. The pore size in the membrane can be precisely controlled which can sieve common salts out of salty water and make it safe to drink.

As the effects of climate change continue to reduce modern city’s water supplies, wealthy modern countries are also investing in desalination technologies. Following the severe floods in California major wealthy cities are also looking increasingly to alternative water solutions.

World Economic Forum: Can Graphene Make the World’s Water Clean?

 

 

 

 

When the common salts are dissolved in water, they always form a ‘shell’ of water molecules around the salts molecules. This allows the tiny capillaries of the graphene-oxide membranes to block the salt from flowing along with the water. Water molecules are able to pass through the membrane barrier and flow anomalously fast which is ideal for application of these membranes for desalination.

Professor Rahul Nair, at The University of Manchester said: “Realisation of scalable membranes with uniform pore size down to atomic scale is a significant step forward and will open new possibilities for improving the efficiency of desalination technology.

“This is the first clear-cut experiment in this regime. We also demonstrate that there are realistic possibilities to scale up the described approach and mass produce graphene-based membranes with required sieve sizes.”

Mr. Jijo Abraham and Dr. Vasu Siddeswara Kalangi were the joint-lead authors on the research paper: “The developed membranes are not only useful for desalination, but the atomic scale tunability of the pore size also opens new opportunity to fabricate membranes with on-demand filtration capable of filtering out ions according to their sizes.” said Mr. Abraham.

By 2025 the UN expects that 14% of the world’s population will encounter water scarcity. This technology has the potential to revolutionize water filtration across the world, in particular in countries which cannot afford large scale desalination plants.

It is hoped that graphene-oxide membrane systems can be built on smaller scales making this technology accessible to countries which do not have the financial infrastructure to fund large plants without compromising the yield of fresh water produced.

Explore further: Researchers develop hybrid nuclear desalination technique with improved efficiency

More information: Tunable sieving of ions using graphene oxide membranes, Nature Nanotechnology, nature.com/articles/doi:10.1038/nnano.2017.21

Journal reference: Nature Nanotechnology

Provided by: University of Manchester