The industrial mass production of graphene is actually not a problem today.
Graphite oxide reduction method, micromechanical exfoliation method, chemical vapor deposition method, epitaxial growth and other methods have actually achieved a certain degree of mass production.
However, the quality of graphene produced by these methods is not high on the one hand, and the graphene produced by these methods is highly contaminated on the other hand.
For example, in the graphene oxide reduction method, the graphene prepared needs to be reduced at high temperature. During this process, incomplete reduction will cause graphene and graphene oxide to coexist, and will also cause graphene to be doped with other impurities.
And if you use a vacuum furnace for reduction, the cost is too high.
This means that this method can currently only produce some low-quality graphene.
This type of graphene basically cannot be used in high-performance electronic devices, energy storage, medicine and other fields. Generally speaking, this type of graphene doped with impurities and contaminated is mainly used in construction, adsorbents, and seawater desalination. , composite materials and other basic fields.
However, the demand for graphene in these fields is actually not large. After all, no matter how low-quality graphene is, it is still graphene, and the price is much more expensive than the technology and materials used in the original industry.
High-quality graphene is the area in high demand.
Whether in the fields of electronic devices, photosensitive components, or aerospace, there is always a gap for high-quality graphene.
However, the industrial mass production of high-quality graphene is an extremely difficult area to solve.
No way, the production process of high-quality graphene is too complicated.
To make high-quality graphene first, you need to prepare high-quality single-layer graphene.
At present, high-quality single-layer graphene is almost always limited by the cavity size of CVD equipment. Existing CVD methods cannot realize the continuous preparation of single-layer graphene.
Although in this field, a country that has secretly begun to discharge nuclear sewage into the sea has demonstrated a so-called 100-meter-long graphene, but the surface of the material has many holes and is completely unusable.
Moreover, the continuous preparation technology and product yield issues of CVD graphene have not yet been solved.
Secondly, high-quality graphene transfer method is a difficult problem to solve. Commonly used wet etching transfer often brings problems such as wrinkles, impurities, damage, etc., making it difficult to achieve large-scale transfer.
The last is a combination of the first two.
That is to realize the continuous preparation and transfer of CVD graphene, and the two are matched and docked to form an automated production technology.
If the first two difficulties are not solved, it can be said that there is no way out for high-quality graphene manufacturing.
In fact, how to evaluate a new technology, especially materials science technology, is not easy in itself.
It requires many supporting conditions.
In fact, many materials science and technology achievements require half of the energy to be spent on pure application testing.
This studio requires a lot of investment. Without sufficient capital support and downstream application support, it is basically useless.
Although graphene is supported by downstream manufacturers, its manufacturing and application is a very difficult problem.
That's why Xu Chuan was very interested in the mass-produced high-quality graphene developed by the Chuanhai Materials Research Institute.
"Go to my office and talk. The results of the experiment here will not be available until around three o'clock in the afternoon. However, I roughly sorted out the relevant production methods and steps yesterday."
Fan Pengyue took off his experimental gloves and brought Xu Chuan to his office.
Turning on the computer, unlocking it, he pulled out an information document from the computer, clicked on it and said: "I haven't had time to print out the information yet, so just make do with the computer and take a look."
Xu Chuan didn't care, took the seat and sat down, carefully reading the information in front of him.
Judging from the data, this method of preparing high-quality graphene was expanded from the method of recycling graphite to prepare graphene from LIBs batteries that was accidentally discovered in the second half of 2019.
In 2019, a researcher named 'Yan Liu' from the institute's lithium-sulfur battery laboratory used materials such as hydrazine hydrate, molten salt hydroxide, and abandoned positive electrode current collector aluminum foil as reducing materials when further optimizing lithium batteries. Agent, trying to modify the LiFePO4 cathode to improve the electrochemical performance and cycle stability of lithium batteries.
However, the expected optimization was not achieved, but unexpectedly, during production testing of the product that failed in the experiment, Yan Liu discovered a carbon film attached to the negative electrode.
After testing, it was confirmed that this was a layer of graphene film material with higher purity.
In this new method of chemical synthesis, the graphite negative electrode undergoes chemical oxidation to obtain uniformly dispersed graphene oxide after electrochemical cycles.
Then the graphene oxide is reduced to graphene through the use of oxidizing agents and reducing agents.
The graphene synthesized in this way has higher purity and is relatively pure and pollution-free.
Of course, it also has many shortcomings.
For example, reducing graphene oxide will involve the use of environmentally unfriendly and expensive oxidants and reducing agents. At the same time, the integrity of the graphene film material structure will also be destroyed due to chemical reactions.
In addition, the transfer of graphene is also extremely difficult.
There are many shortcomings, but this is still a direction worth exploring. This matter attracted Xu Chuan's attention at the time, but at that time, because he was busy with the controllable nuclear fusion project, he could not spare time to conduct in-depth research, so he could only hand over the matter to the Sichuan-Hai Materials Research Institute. Own.
More than a year and a half later, combined with the institute's computational material model, this method of synthesizing high-purity graphene film materials has been greatly improved.
As we all know, there are three difficulties in synthesizing high-quality graphene.
It is extremely difficult to proceed from the continuous synthesis of high-purity single-atom-layer graphene layers to the transfer of thin films and continuous industrialization.
After a year and a half of exploration, the Materials Laboratory has improved this new electrochemical synthesis method.
The first is to further optimize the high purity of graphene, the negative electrode material of the original LiFePO4 battery.
Use high-purity synthetic graphite with a purity of more than 99.999% to replace the original battery negative electrode graphite material.
After all, although the negative electrode of LiFePO4 battery uses graphite, in order to improve the battery performance, it is not high-purity graphite and contains impurities.
Although the number of these impurities is not large, they will also affect the quality of graphene during the synthesis of graphene.
Of course, this is not the key.
The key problem with this method of electrochemical synthesis of graphene is the need for redox and transfer of the synthesized graphene.
The latter is relatively easy to solve, whether it is external microwave transfer or liquid phase peeling method, it is just that the efficiency is not high and there will be problems such as defective products.
As for the former, the reduction of graphene oxide has always been a problem in the industry.
Although there are many choices for reducing agents for graphene oxide, ranging from hydrazine and hydrazine derivatives, to metal hydrides such as sodium borohydride, strong acids, strong bases, alcohols, phenols, vitamin C, reducing sugars (glucose, chitosan Sugar, etc.) can be made.
But no matter which one it is, it has its own shortcomings.
For example, using some acid to reduce graphene will cause the single-layer graphene structure to agglomerate and accumulate due to π-π interactions, leading to problems such as reduced specific surface area, increased resistance, and significantly reduced performance.
Thus limiting its application prospects.
Or use hydrazine or hydrazine derivatives for reduction. Although the graphene obtained solves the agglomeration phenomenon of the product, it also introduces C-N bonds into the graphene obtained after reduction, causing pollution.
Moreover, the hydrazine hydrate used is very toxic and is not suitable for use in large-scale production, industry, and biomedicine.
So Xu Chuan was very curious about how the Chuanhai Institute of Materials solved this problem.
Xu Chuan continued to read along the documents.
In the summary of the reduction method of graphene oxide, he saw the method of reducing graphene oxide by Sichuan Hai Materials Research Institute.
". Use different film assembly methods to modify graphene oxide on a specific electrode substrate to obtain a graphene oxide-modified electrode, and then use this modified electrode as the working electrode of a classic three-electrode electrolysis system in a specific electrolyte solution. Electrolysis reaction to achieve reduction of graphene oxide film ”
"Electrochemical reduction method?"
Seeing this approach, Xu Chuan was stunned for a moment.
He originally thought that the laboratory had found a new type of reducing agent, but he did not expect that they directly broke away from the restrictions of the reducing agent and used an alternative electrochemical method.
[The graphene oxide was ultrasonicated in deionized water for 1 hour, and then modified on a conductive glass substrate, and was tested by extended cyclic voltammetry (CV, -1.0~1.0V, relative to the reversible hydrogen electrode) at 0.1 mol/L An electrochemical reaction occurs in a standard three-electrode cell in a Na2SO4 solution with Hg/Hg2SO4 and Pt electrodes as reference and contrast electrodes to reduce graphene oxide. 】
[The reduction degree of graphene oxide is detected and controlled by measuring the reduction peak and specific capacitance value at -0.75V using X-ray photoelectron spectroscopy (XPS). 】
[Further combined with the electrochemical deposition method, graphene oxide is modified on the conductive glass substrate, and then paired with the glassy carbon electrode in a 0.1mol/L solution, and scanned with an intensity of 0~-0.1V to obtain the results located on the substrate. film on. 】
【.】
The information was not very detailed, not even the electron microscope structural diagrams, but it was enough for Xu Chuan to understand how they did it.
I have to say that this is an extremely clever way to find a new way.
Nowadays, the materials industry has been considering the use of reducing agents or catalysts for the reduction of graphene oxide and the preparation of graphene.
Although microwave reduction, hydrothermal reduction, catalytic reduction and other methods have been studied, these are not actually free from the limitations of reducing agents and catalysts.
This method of electrochemical reduction directly bypasses the influence of reducing agents and catalysts.
Not to mention its efficiency, but without additives such as reducing agents and catalysts, the purity of the reduced graphene is undoubtedly quite high.
After all, during the reduction process, he no longer has the influence of other external additives.
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