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Defective graphene has high electrocatalytic activity

Posted By Terrance Barkan, Thursday, October 15, 2020
Scientists from the Moscow Institute of Physics and Technology, Skoltech, and the Russian Academy of Sciences Joint Institute for High Temperatures have conducted a theoretical study of the effects of defects in graphene on electron transfer at the graphene-solution interface. Their calculations show that defects can increase the charge transfer rate by an order of magnitude. Moreover, by varying the type of defect, it is possible to selectively catalyze the electron transfer to a certain class of reagents in solution. This can be very useful for creating efficient electrochemical sensors and electrocatalysts. The findings were published in Electrochimica Acta.

Carbon is widely used in electrochemistry. A new type of carbon-based electrodes, made of graphene, has great potential for biosensors, photovoltaics, and electrochemical cells. For example, chemically modified graphene can be used as a cheap and effective analogue of platinum or iridium catalysts in fuel cells and metal-air batteries.

The electrochemical characteristics of graphene strongly depend on its chemical structure and electronic properties, which have a significant impact on the kinetics of redox processes. The interest in studying the kinetics of heterogeneous electron transfer on the graphene surface has recently been stimulated by new experimental data showing the possibility of accelerating the transfer at structural defects, such as vacancies, graphene edges, impurity heteroatoms, and oxygen-containing functional groups.

A recent paper co-authored by three Russian scientists presents a theoretical study of the kinetics of electron transfer on the surface of graphene with various defects: single and double vacancies, the Stone-Wales defect, nitrogen impurities, epoxy and hydroxyl groups. All these changes significantly affected the transfer rate constant. The most pronounced effect was associated with a single vacancy: The transfer rate was predicted to grow by an order of magnitude relative to defect-free graphene (fig. 1). This increase should only be observed for redox processes with a standard potential of −0.2 volts to 0.3 volts — relative to the standard hydrogen electrode. The calculations also showed that due to the low quantum capacitance of the graphene sheet, the electron transfer kinetics can be controlled by changing the capacitance of the bilayer.

“In our calculations, we tried to establish a relation between the kinetics of heterogeneous electron transfer and the changes in the electronic properties of graphene caused by defects. It turned out that introducing defects into a pristine graphene sheet can lead to an increase in the density of electronic states near the Fermi level and catalyze electron transfer,” said Associate Professor Sergey Kislenko of the Department for Physics of High-Temperature Processes, MIPT.

“Also, depending on the kind of defect, it affects the density of electronic states across various energy regions in different ways. This suggests a possibility for implementing selective electrochemical catalysis. We believe that these effects can be useful for electrochemical sensor applications, and the theoretical apparatus that we are developing can be used for targeted chemical design of new materials for electrochemical applications,” the scientist added.

Tags:  Battery  bilayer graphene  Graphene  Moscow Institute of Physics and Technology  Russian Academy of Sciences Joint Institute for Hi  Sergey Kislenko  Skoltech 

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Electrochemical doping: researchers improve carbon nanotube transparent conductors

Posted By Graphene Council, Wednesday, July 29, 2020
Skoltech researchers and their colleagues from Aalto University have discovered that electrochemical doping with ionic liquid can significantly enhance the optical and electrical properties of transparent conductors made of single-walled carbon nanotube films. The results were published in the journal Carbon.

A single-walled carbon nanotube (SWCNT) is a seamless rolled sheet of graphene, a list of graphite that is one atom thick. Just as other new carbon allotropes, SWCNTs demonstrate unique properties which can be employed in novel electronic devices that we use in our everyday life. One of the most promising applications is transparent conductors, which can be useful in medicine, green energy, and other fields: here, SWCNT films can replace the industrial standard indium-tin oxide (ITO). They are highly conductive, flexible, stretchable and can be easy doped due to the fact that all atoms in the nanotube are located on its surface.

Doping of SWCNTs allows to significantly increase film conductivity by eliminating the Schottky barriers between the tubes with different nature and increase the concentration of charge carriers. Moreover, the doping process leads to an increase in the transmittance of the films due to supersession of optical transitions.

While adsorption doping remains one of the most promising techniques for SWCNT modification, this method lacks uniformity and reversibility. In the new study, researchers propose a new reversible method to fine-tune the Fermi level of SWCNTs, dramatically increasing the conductivity while the optical transitions are suppressed. For this, they used electrochemical doping with an ionic liquid with a large potential window, which facilitates a high level of doping.

“We placed the SWCNT thin film into electrochemical cell and used standard three electrode scheme to apply potential to the nanotubes. With applying the negative/positive potential to the SWCNT film, an electrical double layer is formed at the SWCNT/ionic liquid interface. The latter acts as parallel plate capacitor causing positive/negative charge injection to SWCNT film surface and consequently the Fermi level shift,” explains Daria Kopylova, the first author of the study and senior research scientist at Skoltech.

The scientists were able to show that their electrochemical method can help achieve extremely high doping levels, comparable to the best results for doped SWCNTs films recently published in the field.

“The process is fully reversible so that it can be used to fine-tune the electronic structure of the single-walled carbon nanotubes in real time. Operating with the gate voltage, you can drive both optical transmittance and electrical conductivity of the films. The results open new avenues for future electronics, electrochromic devices, and ionotronics,” says Albert Nasibulin, head of Laboratory of Nanomaterials at the Skoltech Center for Photonics and Quantum Materials.

Tags:  Aalto University  Albert Nasibulin  carbon nanotube  Daria Kopylova  Graphene  Skoltech 

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Skoltech PhD students win the Haldor Topsoe scholarships

Posted By Graphene Council, Wednesday, June 10, 2020
Haldor Topsoe, a global leader in heterogeneous catalysis, has awarded scholarships to three Skoltech PhD students, Artem Grebenko, Natalia Katorova, and Filipp Obrezkov. Established by the company founder, Dr Haldor Topsoe, over 20 years ago, the Haldor Topsoe PhD Scholarship Program supports young scientists conducting research in heterogeneous catalysis and related fields that are part of Topsoe’s mainstream activity.

We caught up with the winners to find out about the focus and practical impact of their research and their feelings about the award.

Artem Grebenko, Physics PhD Program, Skoltech Center for Photonics and Quantum Materials (CPQM)

Within my study that deals with the heterostructures of metal-organic frameworks (MOF) and graphene, I have developed a new graphene synthesis method and a baseline MOF synthesis technique using a ligand called benzenehexathiol. During the next academic year, I expect to complete the study of the individual properties of graphene and MOF and assemble the first heterostructures by superimposing the MOF and graphene layers.

My study is the first systematic attempt at studying the properties of MOF with a fixed ligand and creating 2D heterostructures from organic materials and graphene. The big idea behind this research is finding the combinations that will uncover the applied potential of new structures. Conducting transparent 2D layers find application in microelectronics and various kinds of optical and gas sensors. At this stage, it is hard to tell exactly what properties those structures may have, but since the change of a ligand converts the MOF from the antiferromagnetic insulator (in the case of chromium) to the superconductor (in the case of copper), this line of research definitely holds a lot of promise.

I am convinced that new materials will transform our lives, as silicon did once. And so did graphene which is yet to make a hit. These are just two examples among a broad diversity of promising materials. Their practical application is still unclear, although MOFs have exhibited excellent catalytic performance in solar panels. I am very excited about the idea to use MOF and graphene structures in microelectronics, for example, transistor channels, sensors or bolometers. In fact, this has been my dream since 2014 when I was still a graduate student. I even attempted to launch a study but faced a lack of equipment and the fact that my project did not fit with the goals of the lab I worked for. It is only after I joined Skoltech that I could fulfil my dream.

The fact that my scholarship application was recognized as an “excellent proposal” by Haldor Topsoe means that I am doing something of value for the industry. While other winners focused on heterogeneous catalysis, Haldor Topsoe’s core research area, I concentrated on making the samples by synthesizing graphene based on heterogeneous catalysis. I derive great pleasure from contributing to science even though I have always thought my work should have a practical purpose. For me, the award is a source of confidence and inspiration for further work. 

Natalia Katorova, Materials Science PhD program, Skoltech Center for Energy Science and Technology (CEST)

My study of potassium-ion batteries has evolved into a startup, K-Plus, that my colleague and I have launched at Skoltech recently and which is strongly supported by the Institute, CEST, and our supervisors and main inspirers, professors Artem Abakumov and Keith Stevenson. Potassium-ion batteries can be a highly cost-effective alternative to modern lithium-ion batteries in stationary energy storage applications, such as solar or wind energy storage solutions. However, the electrochemical performance of a potassium-ion battery, like any other metal-ion battery, is driven by the passivating layer formed by the electrolyte decomposition products on the electrode surface, so in my thesis research, I examine the processes at the electrode/electrolyte interface and try to find ways of improving the properties of the passivating layer.

I have always wanted to work on tasks of high relevance for the global community, and metal-ion batteries are something that everyone in the modern world uses in one way or another. Also, I have always wanted to be part of a cool and inspiring team that would encourage my self-development. This is why I chose to work on this topic in our research team.

We have been actively implementing the results of my study to assemble prototypes of potassium-ion batteries in a prismatic cell. Although they are low-capacity prototypes suitable for LEDs or small electric motors only, they prove that the new technology does work and can be successfully used in the future. Now we plan to tackle a bigger challenge, which is scaling, and assemble larger prototypes with capacities of up to 10-50 Ah. I believe someday you will hear more about the achievements of our potassium-ion batteries!

Winning a competition like this one means a lot for a researcher whose scientific achievements have been recognized by the world scientific community. Also, it means you are going in the right research direction and your findings could have a high impact on our everyday life. I am delighted that the Topsoe Fellowship Program Committee singled out my project from many other applications. 

Filipp Obrezkov, Materials Science PhD program, Skoltech Center for Energy Science and Technology (CEST)

My PhD thesis is devoted to the development of novel organic cathode materials for lithium, sodium and potassium dual-ion batteries. The operational mechanism of such devices differs from working principles of classical metal-ion batteries. In particular, while the dual-ion battery charges, cations and anions are simultaneously transferred from the electrolyte solution to the anode and cathode surfaces, respectively, initiating the electrochemical transformations. As the battery discharges, the reverse process occurs.

This technology is especially interesting scientifically because it might allow to create ultrafast batteries that would take only a few seconds to charge. The design of suitable organic cathode material could potentially facilitate the development of dual-ion batteries with high energy density, which none of the existing solutions can do.

I started to work on this project 3 years ago, as I realized that new batteries with enhanced specific energy, power and stability are one of the most essential tasks of modern electrochemistry and materials science, in particular, due to the fact that organic dual-ion batteries are among the most promising technologies that could advance these research areas quite significantly.

One of the promising potential applications of dual-ion batteries is their utilization in stationary energy storage systems which can allow to enhance the operational efficiency of power plants during off-peak hours.

I am honored to be an awardee of Haldor Topsoe PhD scholarship program because it is a great recognition of high scientific quality of my project, as well as its prospects for the industry.

Tags:  Artem Grebenko  Filipp Obrezkov  Graphene  Natalia Katorova  Skoltech 

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A novel graphene-matrix-assisted stabilization method will help unique 2D materials become a part of quantum computers

Posted By Graphene Council, The Graphene Council, Sunday, August 11, 2019
Updated: Monday, August 5, 2019
The family of 2D materials was recently joined by a new class, the monolayers of oxides and carbides of transition metals, which have been the subject of extensive theoretical and experimental research. These new materials are of great interest to scientists due to their unusual rectangular atomic structure and chemical and physical properties. 

Scientists are particularly interested in a unique 2D rectangular copper oxide cell, which does not exist in crystalline (3D) form, as opposed to most 2D materials, whether well known or discovered recently, which have a lattice similar to that of their crystalline (3D) counterparts. The main hindrance for practical use of monolayers is their low stability.

A group of scientists from MISiS, the Institute of Biochemical Physics of RAS (IBCP), Skoltech, and the National Institute for Materials Science in Japan (NIMS) discovered 2D copper oxide materials with an unusual crystal structure inside a two-layer graphene matrix using experimental methods.

“Finding that a rectangular-lattice copper-oxide monolayer can be stable under given conditions is as important as showing how the binding of copper oxide and a graphene nanopore and formation of a common boundary can lead to the creation of a small, stable 2D copper oxide cluster with a rectangular lattice. In contrast to the monolayer, the small copper oxide cluster’s stability is driven to a large extent by the edge effects (boundaries) that lead to its distortion and, subsequently, destruction of the flat 2D structure. Moreover, we demonstrated that binding bilayered graphene with pure copper, which never exists in the form of a flat cluster, makes the 2D metal layer more stable,” says Skoltech Senior Research Scientist Alexander Kvashnin.

The preferability of the copper oxide rectangular lattice forming in a bigraphene nanopore was confirmed by the calculations performed using the USPEX evolutionary algorithm developed by Professor at Skoltech and MIPT, Artem Oganov. The studies of the physical properties of the stable 2D materials indicate that they are good candidates for spintronics applications.

Tags:  2D materials  Alexander Kvashnin  Artem Oganov  Graphene  MIPT  Skoltech 

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