Graphene has a broad application space and the enormous economic benefits. It is estimated that by 2024, the graphene device expected to replace a complementary metal oxide semiconductor (CMOS) devices, in the field of nano-electronic devices, photoelectrochemical cell, ultralight materials are applied. It is in this context that the current application researches graphene technology in full swing, and the main research focus is concentrated in the energy storage, electrochemical analysis and graphene biosafety and other aspects.
Energy storage material
Development of new energy storage materials is to promote efficient energy storage technology development foundation. In recent years, the field of chemical energy storage graphene focused on hydrogen storage, ultracapacitors manufacture, lithium-ion batteries and lithium --4 aspects of air battery manufacturing. The focus of research is focused on the exploration of graphene preparation methods, experimental study of functionalized graphene and graphene-based nature itself to develop a well-structured high-performance graphene-based energy storage element.
Hydrogen storage aspect. Hydrogen as a secondary energy clean energy is one of the new energy development program indispensable. Which has less wear and tear, non-polluting, high recycling rates, and the use of various forms, etc., known as the 21st century green energy. The use of special materials, adsorption of hydrogen is a new hydrogen storage method, the results show that the hydrogen storage capacity currently using activated carbon, fullerenes and carbon nano-fiber and other carbon materials did not reach the ideal state, but as sp2 hybridized carbon basic structure of graphene unit since its inception, the show compared to other carbon materials more excellent hydrogen storage properties, and actively explore the domestic and foreign scholars and therefore graphene composite structure and hydrogen storage in terms of potential. Some scientists combined palladium nanoparticles to graphene material, made of two-dimensional graphene nanosheets, a new generation of hydrogen storage material and the activated carbon material mixed. The results show that hydrogen storage capacity of the hydrogen storage material at a pressure of 10MPa state can reach 0.82% (mass fraction), improved nearly 49% compared to pure palladium nano-material that is not only good storage properties and adsorption reversible high degree.
Supercapacitor aspect. Super capacitor can be called electric double layer capacitor is a new type of energy storage device having high charge and discharge efficiency, environmental protection, safety and reliability, as well as cycle reversibility, etc., it can be widely used in mobile communications, computer technology, aerospace national defense and science and technology. So the support of independent electrodes must have high mechanical strength and large capacitance characteristics. Compared to other carbon material graphene high conductivity, large surface area, and stable chemical structure, is more suitable as a supercapacitor electrode material. Most research point of view that the high-temperature environment is a necessary condition for the redox chemistry of graphene, but there are scientists in a vacuum environment, and successfully prepared graphene under this condition is far below the theoretical critical peeling temperature 200 ℃. High-temperature method were compared to graphene, by this method the system out of graphene, which is higher than the capacity reaches 279 F / g.
However, the current graphene, metal oxide and conducting polymer composites research is still confined to the laboratory, not yet resolved how good the preparation of large-scale problems and quality of graphene composites of graphene-based supercapacitors the volume is also more than the lack of research performance.
Lithium-ion batteries. Lithium-ion batteries by moving lithium ions between the positive and negative poles to work, so the conductivity of battery cathode materials is closely related to the lithium-ion battery energy density and power performance. In fact, most of the electrode material are specific capacity and the theoretical capacity than can be achieved far, especially in the high-current charge and discharge, the specific capacity of the electrode material will be substantially reduced. Graphene material due to have excellent electron conductivity, is applied to the study of the lithium ion battery. Cathode material graphene layer is applied to the battery, the battery can not only reduce the interface resistance, ease of lithium ions between the positive and negative poles of the battery conductivity, the metal oxide can also help slow down the rate of dissolution of the phase transition, in order to ensure a lithium battery electrode holding structure in the electric cycle period. Some scientists ternary co-assembly method, tin oxide and graphene together with the synergistic surfactant Multi prepared three yuan ordered nanocomposites (see Figure 1), the specific capacity of the material for the electrode can reaches 760 mA • h / g, and the material is a good buffer material, help to improve the cycling stability of lithium-ion battery electrode materials.
Lithium - air batteries. Lithium - air batteries as ideal for high energy chemical power, in recent years become a hot topic. At present, graphene lithium - air battery research applications, showing outstanding advantages, which not only constitute a battery cathode material, more show remarkable catalytic activity. In lithium - air battery, graphene as a catalyst or catalyst substrate demonstrate its potential benefits, can improve the catalytic efficiency, and continuously improve the lithium - air battery cycle performance, which enhance the characteristics of the lithium surface area than the huge and a porous system - air discharge capacity. Scientists alkyl carbonates in the electrolyte is a lithium air battery, the graphite nanosheets (NGS) as the cathode catalyst proved Vulcan XC-72 as compared to the carbon electrodes, electrode NGS better cycle performance, lower overpotential. Some scientists have prepared an air electrode graphene foam lithium-air batteries, experiments show that lithium - air battery 20 cycles under the current circumstances, its only loss of cycle efficiency by 20%, and the discharge voltage at 2.8V .
Electrochemical Analysis
Graphene in an electrochemical analysis and is mainly used in the detection and analysis based on the target molecule as a biological electricity direct electrochemical analysis based on respect and support material graphene optically transparent electrodes.
Target molecule direct electrochemical analysis. Target based on the target molecule direct electrochemical detection analysis include: inorganic small molecules, small organic molecules, and redox proteins and nucleic acids and other biological macromolecules, such as DNA and hemoglobin. Protein adsorption characteristics may make graphene is an ideal material for the study of protein electron transfer in graphene. If scholars chemically reduced graphene oxide modified glassy carbon electrode (CR-GO / GC) as a new electrode system, proposed a new experimental platform electrochemical sensing and biosensing. Others studied graphene oxide (GO) direct electrochemical behavior of cytochrome C, myoglobin and horseradish peroxidase (HRP) and other three kinds of metal electrode modified protein and found that GO can promote electron transfer dynamics, and its biological activity is almost unaffected.
Bioelectrical analysis support material / Bacteria electrode carrier material. The enzyme electrode is one of the important biological analysis. Defects and oxygen-containing groups GO surface has a chemical and electrochemical reactivity, can be chemically bonded fixed biomolecules for biosensors. Research on graphene-based material non-covalent immobilization for biosensors there are many examples; immune sensing is an important category of biological affinity sensing plays an important role in biological assays; graphene oxide material developed sandwich-type immune sensor, the sensor is excellent properties because graphene has fast electron transfer rate and large specific surface area.
Graphene-based optical transparent electrode. Conventional optically transparent electrode mainly of indium tin oxide coated quartz glass and ordinary, mainly used for LCD, an organic light emitting diode (the OLED), a touch screen and a solar cell electrodes. Indium tin oxide glass following problems: indium reserves and less expensive, fragile and indium tin oxide coating film often require a vacuum environment, the lack of flexibility of the glass substrate, limit the optically transparent indium tin oxide electrode application. The atom-thick graphene due to good transparency, high conductivity, high mechanical strength, low production cost, is the production of light-permeable electrode alternative materials, especially the production of flexible light-permeable electrode ideal material. Based on optically transparent electrode material graphene can be used for dye-sensitized solar cell. Scientists graphene oxide after chemical reduction obtained graphene light-permeable membrane electrode, the conductivity of 550S / cm, in 1000 ~ 3000nm wavelength transmittance greater than 70%, although the translucent material such as indium oxide ratio low , but the resulting current density ratio of indium oxide high, and has a high chemical and thermal stability.
Graphene biosafety
Study on cytotoxicity of. Analysis of cytotoxic graphene and its composites help determine the extent of its biological safety. Huang Qing group CAS Shanghai Institute of Applied Physics of graphene research has been concerned cytotoxicity, and has published a series of research works. Group through a lot of experiments, cells were found after the graphene oxide (GO) nanosheets layers of different concentrations were mixed, showing only the lifting cell activity, the cells did not vary GO concentration and death, visible GO It has good biocompatibility. On the other hand, the same concentration of GO and reduced graphene oxide (RGO) showed a different cytotoxicity, and varying degrees of cytotoxicity graphene oxide also will be different. Hu et al found that, due to the GO material having good adsorption, the cell culture medium can be adsorbed proteins cladding layer is formed, inhibiting its interaction with the cell membrane, to reduce the cytotoxicity of GO. There are other studies showing the size of the GO would have a greater impact on its cytotoxicity, that the smaller the size of GO, their cytotoxicity is smaller. Currently, there are a small number of researchers believe that GO cytotoxicity is likely to come from the interaction between the material and the cell membrane, but scholars have not yet graphene membrane materials and methods of interaction and mechanisms of in-depth study. With graphene and its composites are increasingly used as drug material phenomenon, researchers have begun to focus on a wide range of compatibility of the material itself and the blood.
Animal studies of toxicity. Graphene Composites and animal toxicity is one of the focus of academia. Studies have found that GO mammalian lung organ toxicity; but studies have shown that, through the modification of GO can avoid lung toxicity to mammals to some extent. In addition, some scholars also analyzed relevant factors that animal toxicity, and others compared under different conditions GO animal toxicity, animal toxicity and its comprehensive GO electron transfer process inside the cells was studied. In normal circumstances, the body's internal hydrogen peroxide (H2O2) is limited, and cytochrome c as a biological oxidation process of electron mediator, has been attached to the inner wall of the cell mitochondria, and a small amount of H2O2 catalytic GO does not cause cell cytochrome c leak, induce apoptosis. However, oxidative stress environment, the electron transfer in vivo, the GO may be a large number of electron transfer to oxygen molecules, generating a large amount by H2O2, in the interior of the cell accumulate to a certain extent, causing leakage of cytochrome c, cell ultimately can not to avoid the result of apoptosis.
Study of microbial antimicrobial regard. Graphene their derivatives not only have good biocompatibility, also exhibit outstanding antibacterial interaction with microorganisms. Huang Qing group in 2010 for the first time revealed the antibacterial properties of graphene materials, experimental data demonstrate that in graphene nano-doped liquid medium, E. coli survival only about 10%. Currently, research on the antibacterial graphene and its composites is mainly focused on the following two aspects: on the one hand, due to the graphene PAH (Polycyclic Aromatic Hydrocarbons, PAH) structure has excellent chemical modification function, academia has been committed graphene antibacterial materials used in manufacturing, to explore a possible large-scale preparation of new composite nano material way. On the other hand, the researchers then by comparing the different levels of graphene oxide antimicrobial, antibacterial principle and in-depth analysis to explore the mechanism of graphene materials in order to provide reference for maximizing graphene antibacterial function.
It found that graphene material significance, even herald the rise of a new round of carbon chemistry revolution, triggered a scientist of great research interest. Graphene has good electrical and thermal conductivity, light transmission, anti-bacterial, and the large specific surface area and other characteristics, in terms of energy storage, electrochemical analysis have shown a good prospect, worthy of academic study continue to pay attention. However, graphene still exist in the market and the product of the process, many problems to be solved, graphene industrial production has yet to achieve its scale preparation, the use of functional needs further exploration, scientists have to deal with graphite ene systematic research to promote the progress of all aspects of the performance of the graphene, and promote their products, commercialization of the process. (Source: "The new materials industry,")