New applications of graphene in electrochemical energy storage.

Researchers from all over the world study of graphene with great enthusiasm, on the one hand, focus on its unique structure and excellent properties, on the other hand is to focus on the improvements in the way of life in the social production and even subversive application potential.
This is one of the most important reasons for the work of and reGeim and KostyaNovoselov of the university of Manchester in the UK to be recognized by the Nobel committee.
Graphene potential important frontier application involves many aspects, this article from the electrochemical energy storage, desalination, and biological applications introduced nearly two years since research institutions at home and abroad and some research progress and application situation.

1. Electrochemical energy storage.

Industry experts believe that electrochemical storage is the most likely way to achieve mass production of graphene, especially in the direction of supercapacitors and batteries.
According to India market research firm Azoth Analytics released in August 2017, graphene battery research report, the next seven years, the global graphene battery (including lithium ion battery, lithium battery and super capacitor, lead-acid batteries, etc.) the market average annual compound growth rate of 38.34%.
The report points out that the increase in sales of electric vehicles and the increase in demand for portable consumer electronic products are the main driving force for the sustained and rapid growth of the graphene battery market.
In addition, the rapid increase of renewable energy power stations is also an important factor.
The European region is the largest market for graphene batteries in 2016, and by 2024, the asia-pacific region is expected to have the highest rate of growth due to consumption and clean fuel demand.
Companies such as XG Sciences, Cabot and Graphene 3D Lab from the us will become the world's leading suppliers of Graphene battery technology.

1. Electrode material

The university of Manchester researchers funded by the national institute of graphene using simple expandable screen printing technology, the fabric surface directly printed on similar flexible battery equipment, not only like ordinary fabric soft, also can give the wearable device power supply.
The supercapacitor component is the technical approach to implement the scheme [[3]].
Tsinghua university researchers used with high specific surface area of the stack of graphene, developed the nanostructures of lithium-ion battery anode material, can inhibit the growth of dendrite in lithium batteries, improve their electrochemical performance.
Because the pore volume of non-stack graphene reaches 1.65 cm2/g, the stable circulation of the anode can reach 4.0 mAh/mg, 10 times more than the graphene anode in lithium battery [[4]].
At Stanford university in the United States use hydrophobic, low gas permeability of graphene parcel lithium alloy nanoparticles, made of lithium metal/graphene anode materials, used to lithium iron phosphate (LiFePO4), vanadium pentoxide (V2O5), sulfur (S) for the anode material of lithium battery, the contrast experiment shows that under the high current density of charge and discharge cycle after 400 time, the battery can keep 98% of the initial capacity [[5]].
The university of California, Los Angeles team using niobium pentoxide (Nb2O5) mixed with the graphene oxide, is obtained by reduction reaction preparation of three-dimensional porous graphene composite material, solved the difficult problem of electrode performance with load dramatically, for the first time in high load (> 10 mg/cm2) in the electrode at the same time to realize the high capacity and high power characteristics [[6]].
South China university of technology and the university of south Carolina, united team through solvent hot method, preparation of graphene coating antimony selenide (Sb2Se3) dimensional nanostructures, good performance and cycle performance.
New research ideas and theoretical support are provided for the development of electrode materials with excellent properties of sodium storage.

2. Super capacitor

The shenzhen graduate school of tsinghua university researchers using graphene oxide, and with the aid of titanium dioxide auxiliary ultraviolet light reduction, building of sandwich structure is obtained "excluding conductive additives, binder, the commercialization of the diaphragm and fluid collection" super capacitor.
The capacitor has good mechanical stability, 90 ° and 180 ° bend, the electrochemical performance is not reduced.
Metal research institute, Chinese academy of sciences and the university of nanjing united team in the framework of high conductive graphene bubble, design the preparation of a 3 d graphene network structure of mixed nitrogen, nitrogen doping level of 15.8% (atom percent).
When used as electrode materials for supercapacitors, the ratio of capacitance in neutral, acidic and alkaline electrolyte was 245, 332 and 380F/g, respectively.
In actual application of device to achieve the specific capacitance values of 297 F/g, charging and discharging capacitance remain at a rate of 93.5% after 4600 times, just 0.4 Ω internal impedance.

Use (class) battery materials and materials (class) capacitor assembly of ion capacitor is also a hot research topic, this kind of devices offer the advantages of battery and super capacitor, which is of high energy density, and high rate, long service life.
The university of California, Los Angeles in mesoporous single crystal titanium dioxide/graphene composites as anode, commercial activated carbon as anode, was prepared with high working voltage (1 ~ 3.8 V) of sodium ions capacitor.
By optimizing the content of graphene, high storage capacity (126 mAh/g), high magnification (20C, about 1min) and long cycle life (18 000 cycles without obvious attenuation) can be achieved.

Ii. Seawater desalination and other separation membranes.

The search for water has become an increasingly urgent task as population growth and , to some extent, reduce water supplies due to climate change.
The earth's freshwater resources account for less than 3% of the total water body, and desalinating seawater could be one way out.

"Multi-functional" graphene is also involved in this field.
Japan shinshu university of Pennsylvania state university and the joint team used spraying technology solutions in graphene oxide and spray a mixture of layers of graphene to less after pva modification of polysulfone resin membrane, which can realize separation of 85% salt and 96% dye, although after processing water temporarily can't drink, but can be used for agricultural irrigation.
At the same time, the addition of graphene can improve the tolerance of the membrane to chlorine [[4]].
Beijing university using plasma enhanced chemical vapor deposition method was prepared with continuous multistage structure of pore graphene bubble: in the framework of porous foam graphene on build the graphene nano vertical array structure.
The light foam has good corrosion resistance and can be used in the heat transfer application of sewage treatment and seawater desalination.
In seawater desalination, the solar steam conversion efficiency is more than 90%, higher than most existing photothermal conversion materials, and has good circulation and durability.
Engineers at the university of Washington in the United States use nanofibers produced by bacteria to make a 2-layer biofilm that can be used to purify water.
Among them, the upper layer contains the oxidized graphene which can absorb the heat from the solar energy, and the lower layer is the original cellulose.
The purification process is similar to that of sponges, where the impurities are left behind and the clean water evaporates to the top.
, according to a study at the university of Manchester, England, after treated with different humidity of graphene oxide layer spacing can be controlled in 0.64 ~ 0.98 nm, the macro thickness is 100 microns of graphene oxide film with epoxy resin encapsulation after physical limit, which can effectively inhibit the swelling in the water, the sodium chloride (NaCl) withholding rate is 97%.
The decrease of the channel will decrease the ionic permeability in exponential form, but it does not affect the mass transfer speed of water molecules.

Apart from seawater desalination, oil and water separation is one of the hot spots.
University of science and technology of China for the first time in the porous hydrophobic oil adsorption material is introduced into the joule heating effect, using centrifugal auxiliary dip coating technology, the design which has the function of heating and oil-water separation in situ graphene functionalization sponge, oil absorption time was reduced by 94.6%.
With the design of array electrode, large-scale production can be realized, which has a wide application prospect.

Biological applications.

Single-layer graphene is carbon atoms with sp2 hybridization together as a single atomic layer, thickness of only 0.335 nm, has a great specific surface area, can load including drugs, biological activity, fluorescent molecules, such as the electrochemical activity of the molecules and metal atoms, a variety of molecules, implementation in targeted drug delivery, cell imaging, tumor treatment, and the application of biological molecular detection, separation, and other fields.
A study by the university of Illinois at Chicago found that brain cells interact with graphene to differentiate between active cancer cells and normal cells.
When graphene encounters cancer cells, the latter redistributes the former's charge, making it more negatively charged on the surface and releasing more protons.
Rutgers university, new Brunswick campus of researchers using human breath condensate, we design a biosensor based on graphene, can early detection of asthma, to improve the treatment of asthma and other respiratory diseases.

Graphene quantum dots, quantum dot is expected to replace heavy metal which has adjustable photoluminescence properties of good biocompatibility and low cytotoxicity, and , in cell imaging, biological sensors and drug delivery has made certain research results.
In the "2017 China (wuxi) graphene innovation business conference", the Chinese academy of sciences, Shanghai institute of microsystem and information technology entrepreneurial teams shows "doped graphene quantum dots in the very early detection of the tumor and the application of visual intelligent treatment" project results, by using graphene quantum dots to tumor found and the treatment process, greatly improve the discovery rate and the treatment effect of tumor.

Iv. Miscellaneous

In addition to the applications mentioned above, graphene has many emerging applications in image sensing, terahertz devices, electromagnetic shielding and other fields.
Spain photon science institute researchers will metal, PbS colloidal quantum dot semiconductor materials blended with graphene, and placed in a CMOS wafer, and image processing chip packaging unit is connected to a readout circuit, can develop induction of 300 ~ 2000 nm wavelength of high resolution image sensor, fully cover the whole visible light range [[4]].
Italy's national research council institute of nano science, was prepared by a joint team of the university of Cambridge with a terahertz saturable absorber, compared with other equipment, its absorption modulation orders of magnitude higher level.
Institute of China electronics technology group co., LTD. 13 and nano technology and nano bionic research institute, Chinese academy of sciences, suzhou developed can work at room temperature environment of low impedance and high sensitivity graphene terahertz detectors, realize the extrapolation mixing and subharmonic mixing detection, the highest detection frequency up to 650 GHz, sensitivity and working frequency are achieved similar detector of the highest level.

Carbon nanotubes, graphene and other traditional single carbon materials are limited by a single structural feature, and the electromagnetic shielding efficiency is more difficult to further improve.
To solve this problem, researchers at northwestern polytechnical university by chemical vapor deposition method, the graphene nano hybrid connection with carbon nanotubes, using hybrid body has defects across scales, implements the interface to the ascension of shielding effectiveness of electromagnetic wave absorption.
The study shows that compared with the same density carbon nanotube foam, the electromagnetic shielding effectiveness of the hybrid foam is increased by 80% ~ 110%, which is the highest value of the current report compared to the shielding effectiveness of 6,600 dB/ (g/cm3).

V. prospect

Since 2004, graphene has emerged as a stable form, with its unique physical and chemical properties and two-dimensional structure attracted by the world's scientific research community and industry.
Both theoretical and experimental studies show that graphene has great scientific significance and application value.
In recent years, the research progress of graphene in the fields of preparation, characterization and application has been emerging, and many research achievements have been made. However, there are some problems.
It can be said that there is still a long way to go from the laboratory to the market.
For example, many graphene products are polycrystalline complexes, rather than complete single crystals, which can make the excellent performance greatly reduced.
In addition, graphene has no gap, which is a short board in the electronic field. If you want to replace the silicon base transistor, you need to implant the bandgap. However, this is not easy.
Therefore, "graphene two-dimensional material" has become a new research hotspot.
At present, researchers around the world still need to work hard to realize graphene's real use at an early date.
With the popularity of energy storage system in the terminal application field and from the construction of network infrastructure, as well as a significant increase of renewable energy power generation, power grid dimensions increased demand and energy storage battery energy storage system continue to reduce production costs, energy storage market will be further developed.
To promote the development of the energy storage technology, promote the energy storage market application, the third session of Shanghai international energy storage technology and application exhibition (2018) on 23-25 August 2018 was held at Shanghai new international expo center, more than 500 enterprises will appear and display area of 60000 square meters.

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