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The latest research progress of graphene: three-dimensional graphene bulk material breaks through Nanocomposite properties

2020-04-23 15:24:45 嘉兴恒隆复合材料有限公司 Viewd 990

Graphene is a single-layer carbon atom surface material exfoliated from graphite material. It is a "super material" that is harder than diamond and can stretch like rubber. Its electrical and thermal conductivity exceeds that of any copper wire, and its weight is almost zero.

Graphene has been widely used in the field of electrochemistry due to its advantages such as high conductivity and high surface area. However, when assembling graphene into a macroblock electrode, the contact resistance between the sheets is large and the agglomeration is serious, resulting in a decrease in electrochemical performance. For these problems, scholars have proposed the concept of three-dimensional graphene bulk material, referred to as three-dimensional graphene, that is, a graphene porous bulk material with graphene sheets as the basic structural unit and a three-dimensional network structure with sp2 covalent bonds. .

The three-dimensional graphene prepared by the current liquid phase assembly method, template vapor deposition method and the like has weak internal connection, low production efficiency, and many impurities. Recently, the research group of Professor Wang Xuebin, School of Modern Engineering and Applied Science, Nanjing University reported a zinc-induced layered carbonization method, which can efficiently prepare high-quality three-dimensional graphene bulk materials at low cost. Its product is called zinc-induced three-dimensional Graphene ZnG.

Professor Wang Xuebin's research group has pioneered the use of glucose and other cheap organic materials as carbon sources, and developed a chemical foaming method to prepare advanced foam materials such as three-dimensional stretched graphene (Nat. Commun., 2013, 4, 2905; Nano Energy , 2015, 16, 81; Bull. Chem. Soc. Jpn., 2019, 92, 245). The foaming method produces foam with higher yield, lower cost, and stronger structural integrity, but the foaming process has poor controllability.

The team of Wang Xuebin has recently developed a zinc-induced layered carbonization method, namely zinc-assisted solid-state pyrolysis (ZASP). Using glucose as the carbon source and zinc powder as the layering agent; while heating the glucose to pyrolyze to generate coke, metallic zinc evaporates and penetrates into the coke. Further, driven by surface tension, the mixture of zinc and coke delaminates to form a sandwich structure; or, to put it visually, zinc cuts coke into several thin layers. In the subsequent heating process, the thin layer of coke is converted to graphene, and the volatilization of zinc is completed. Liquid zinc completely converts coke to graphene, and there are no by-products such as solid carbon or bulk carbon in the product, eliminating the problem of solid carbon by-products that were usually present in the pyrolysis process of solid carbon sources. This process is similar to the dissolution of coke furnace lining in blast furnace ironmaking. The layering effect of zinc focusing is a new type of metal-carbon interaction, which is different from the previous metal-carbon interaction types such as metal and carbonization reaction and alloying. Therefore, the zinc delamination effect is different from the usual template process.

In addition, zinc can catalyze the carbonization and graphitization process; zinc can also be directly volatilized and deposited in the exhaust gas system, without any treatment directly recycled, not only avoid the troublesome wet treatment in other methods, but also truly achieve recycling, greatly reducing Cost. The zinc method three-dimensional graphene product ZnG has a high specific surface area, excellent thermal stability, and excellent electrical conductivity in air and in an electrolyte. The work also demonstrates that ZnG is used as an electrode for electric double layer supercapacitors, achieving excellent energy density, power density, and cycle life. This work was published in "Advanced Materials" with the title "Zinc-Tiered Synthesis of 3D Graphene for Monolithic Electrodes" [Adv. Mater. 2019, 31(25), 1901186].

The work first studied the zinc-induced layered carbonization method ZASP. In a typical production process, glucose and zinc powder are mixed, pressed into a desired shape, and heated to 1200°C under an inert atmosphere to directly obtain a three-dimensional graphene block ZnG with a good graphitization degree. The ZASP process has a higher yield, and ZnG products can maintain the original design appearance. ZnG is a three-dimensional continuous network structure, each cell is adjacent to five or six cells, and the whole tends to be closely and orderly arranged. The cell walls of ZnG cells are sp2 mono/oligoatomic layers with an average thickness of 2.2 nm. In ZnG, there are no solid ribs, solid particles and other impurity morphologies of the previous solid carbon source pyrolysis method. Compared with 3DRGO 3DGO, ZnG has higher chemical purity, specific surface area, electrical conductivity, and thermal stability.

This work further demonstrates the symmetrical supercapacitor device assembled with ZnG. Electrochemical tests show that ZnG-based supercapacitors have excellent specific capacitance (up to 336 F/g at 0.5 A/g), maximum power density (625 kW/kg), energy density (11.7 Wh/kg), and stable cycling Performance (when the potential window is 1.4V, the cycle is 267,000 cycles; at the rated voltage, it can be cycled more than 1 million cycles), and the full life cycle energy storage density (15 MWh/kg) is far superior to traditional energy storage devices.

The zinc layering effect unexpectedly creates a three-dimensional graphene with a full film structure, which makes the ZASP method stand out from many preparation methods. The product ZnG has high chemical purity, morphological purity, surface area, electrical conductivity, and thermal stability. At the same time, zinc is also a catalyst for carbonization and graphitization reaction, and is a reagent that can be recycled on site. ZASP has good reliability and controllability, using solid carbon source, can be mass-produced. The production process does not require wet treatment, and the process flow is compatible with existing powder metallurgy, investment casting and other process facilities, which opens the way for large-scale industrial production.

Professor Wang Xuebin of the School of Modern Engineering and Applied Science of Nanjing University is the corresponding author of the thesis. This research has been supported by the National Overseas High-level Young Talents, the National Natural Science Foundation of China, Jiangsu Double Innovation Talents, and the Jiangsu Natural Science Foundation.

Figure 1. Synthesis method, structure, morphology and Raman spectrum analysis of three-dimensional graphene ZnG. a-c) Synthesis process and optical photos; d-g) SEM, STEM, TEM pictures; h) HRTEM image of the graphene film of a single cell wall; i) Raman spectrum.

Figure 2. The layering effect of zinc focusing. a) TG curve; b) SEM and EDS mapping of 700 ℃ intermediate product; c) TEM image of 700 ℃ intermediate product; d) c image carbon film (in zinc background) generated in situ by the sample, that is, the layering process; e) EELS mapping; fi) Schematic diagram of layering effect; jm) Other types of metal-carbon interactions. These processes cannot avoid the formation of solid carbon or bulk carbon when using solid carbon sources.

Figure 3. Performance of ZnG-based supercapacitors. a) CV curve; b) Specific capacitance-sweep relationship; c) Cyclic stability at 1.4V; d) Terminal voltage change of constant potential charge-constant current discharge; e) Ratio of voltage drop to discharge current; f ) The DC internal resistance and its composition obtained by theoretically fitting the e diagram; g) Ragone diagram; h) trade-off diagram of maximum power density-energy density; i) comparison of the full life cycle energy storage of various devices.

Tobin Filleter Research Group, University of Toronto, Canada-Graphene Fatigue

Materials produce mechanical fatigue under cyclic loads that are far below the ultimate tensile strength, so understanding this behavior is critical to assess long-term dynamic reliability. The fatigue life and damage mechanism of two-dimensional materials are currently unclear, which is a research hotspot in the field of machinery and electronics. Here, we conducted fatigue studies on free-standing 2D materials, especially graphene and graphene oxide (GO). Using an atomic force microscope, the average stress of single-layer and multi-layer graphene is 71 GPa, the stress range is 5.6 GPa, and its fatigue life exceeds 109 cycles, which is higher than any material reported so far.

The fatigue failure of single-layer graphene is global and catastrophic, with no progressive damage, and molecular dynamics simulations show that this occurs before stress-mediated bond reconfiguration near the defect site. In contrast, the functional groups in GO have a local progressive fatigue damage mechanism. This study not only provides basic research on the fatigue enhancement behavior of graphene nanocomposites, but also provides a starting point for the dynamic reliability evaluation of other two-dimensional materials.

Fig. 1 Fatigue test of 2D materials.

Fig. 2 Fatigue of graphene.

Fig. 3 GO fatigue.

Fig. 4 Fatigue fracture morphology.

Fig. 5 MD fatigue simulation of graphene and GO.

Graphene anti-fog goggles

Learned from the Jiangnan Graphene Research Institute in West Taihu Lake, in order to solve the problem of fog caused by the frontline medical staff wearing goggles, Feng Guanping, the founder of China's graphene industry development and the honorary dean of Jiangnan Graphene Research Institute, is organizing Tsinghua University Chang Geng Hospital , Jiangsu Provincial Graphene Innovation Center, Eiwang Technology and many other scientific research teams, all efforts to develop graphene anti-fog phototherapy goggles.

The project has completed prototype production. Graphene anti-fog phototherapy goggles make full use of the functionalized graphene super-hydrophilic characteristics and electrothermal characteristics, which can help medical grade goggles to effectively prevent fog and enhance transparency, relieve eye fatigue, eliminate eye puffiness, and improve the efficiency of medical staff .

It is reported that during the SARS period in 2003, Feng Guanping, then dean of the Research Institute of Tsinghua University in Shenzhen, led the research team for a week in a row and completed the development and manufacturing of the first infrared rapid body temperature detector in China for customs clearance from Shenzhen to Hong Kong, and achieved obvious results. . From April to June of that year, the Institute produced a total of 20,800 infrared thermometers of various types, which detected more than 30 million passengers and detected nearly 10,000 people with abnormal body temperature.

"In the current fight against the new coronary pneumonia epidemic, infrared temperature detectors are still widely used, and I am very proud." Professor Feng Guanping said that the graphene goggles developed will be released to the relevant hospitals as soon as possible to win the epidemic prevention and control battle Contribute.

Graphene medical protection products

This Haodeli Intelligent Technology Co., Ltd., which produces graphene medical protection products, is located in Yiqiao, Xiaoshan. The hard core helps fight the epidemic! Mr. Ma Rende, chairman of Hao Deli Intelligent Technology Co., Ltd., gave full play to the advantages and functions of the Hong Kong and Macao committees, fully protected the production of masks, protective clothing and other key anti-epidemic materials, and actively donated donations to help prevent and control the epidemic.

Hao Deli is currently working overtime to produce graphene protective equipment, and donated to provincial and municipal medical institutions and related units. A total of 20,000 pieces of graphene masks and 553 pieces of graphene smart assault garments have been donated to the municipal health and health committee, the first hospital of Zhejiang University, the second hospital of Zhejiang University, the Shao Yifu Hospital, the fourth hospital of Zhejiang University and other medical institutions and units, with a total value of more than 2 million yuan. .

The company mainly produces graphene protective clothing and other medical products. The advantages of graphene protective clothing are light weight and good isolation effect, which is several times higher than the similar products. The planned annual output is 8 million pieces. Graphene masks can theoretically be worn for 24 hours, the isolation level can reach 99%, and the planned annual output will reach 100 million. The goggles made of graphene have the advantages of no fog, light weight, comfortable wearing, etc., beyond the various indicators of medical isolation, and are now ordered by the United States, Iran and other countries.

Yadi's newest graphene battery

The Yadi G5 graphene version still follows the Yadi G5 Founder appearance, high-end atmosphere, the surface is imported from Sweden Berg, paint, PU800 baking process + 9 spray grinding process, 1000W high-performance power motor, with Yadi's latest research and development Graphene battery with strong power and easy climbing; 12-inch vacuum tires, moisture-proof and anti-skid, strong grip; front and rear opposed cylinder disc brakes, 220mm disc brake discs plus opposed cylinder piston brake calipers, bidirectional braking The brakes are more sensitive. In the extreme endurance test of minus 6℃, Yadi G5 graphene version of the portable electric motorcycle still ran out of 54.74km.