Chapter 466: Amazing Preparation Method!
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. In 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 wrinkles, impurities, damage and other problems, 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 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 look at it."
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 positive electrode waste current collector aluminum foil as reducing materials when further optimizing lithium batteries. Agent, trying to modify the LiFePO4 positive electrode 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 anode 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 because he was busy with the controlled nuclear fusion project at that time, he could not spare time to study it in depth, so he could only hand it over to the Chuanhai Materials Research Institute.
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 the synthesis of high-quality graphene.
From the continuous synthesis of high-purity single-atomic layer graphene layers to the transfer of thin films and continuous industrialization, it is extremely difficult.
After a year and a half of exploration, the Materials Laboratory has improved this new electrochemical synthesis method.
First, the original graphene negative electrode material of the LiFePO4 battery is further optimized to a high purity.
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 the 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 small, they will also affect the quality of graphene during the synthesis of graphene.
Of course, this is not the key.
The key problem of this electrochemical method of synthesizing graphene is the need for redox and transfer of synthesized graphene.
The latter is relatively easy to solve, whether it is external microwave transfer or liquid phase exfoliation, it can be achieved, but the efficiency is not high, and there will be problems such as defective products.
The former, the reduction of graphene oxide, has always been a difficult problem in the industry.
Although there are many options for reducing agents for graphene oxide, from hydrazine and hydrazine derivatives to metal hydrides such as sodium borohydride, strong acids, strong bases, alcohols, phenols, vitamin C, reducing sugars (glucose, chitosan, etc.), etc. can be done.
But no matter which one, it has its own shortcomings.
For example, the use of some acids to reduce graphene will cause the single-layer graphene structure to agglomerate and accumulate due to π-π interactions, resulting in a reduction in specific surface area, an increase in resistance, and a significant reduction in performance.
This limits its application prospects.
Or using hydrazine or hydrazine derivatives for reduction, the obtained graphene can solve the agglomeration phenomenon of the product, but it also introduces C-N bonds into the reduced graphene, causing pollution.
Moreover, the hydrazine hydrate used is very toxic and is not suitable for large-scale production, industry, and biomedicine.
So Xu Chuan was very curious about how the Chuanhai Materials Research Institute solved this problem.
Following the document, Xu Chuan continued to read.
In the summary of the reduction method of graphene oxide, he saw the way Chuanhai Materials Research Institute reduced graphene oxide.
". Use different film assembly methods to modify graphene oxide on a specific electrode substrate to obtain an electrode modified with graphene oxide, and then use this modified electrode as the working electrode of the classic three-electrode electrolysis system to perform an electrolysis reaction in a specific electrolyte solution, thereby realizing the reduction of graphene oxide film."
"Electrochemical reduction method?"
Seeing this method, Xu Chuan was stunned.
He originally thought that the laboratory had found a new type of reducing agent, but he didn't expect that they directly broke away from the limitation of the reducing agent and used an alternative electrochemical method.
[etc. ultrasonicated graphene oxide in deionized water for 1h, then modified it on a conductive glass substrate, and reduced graphene oxide by electrochemical reaction in a 0.1 mol/L Na2SO4 solution with Hg/Hg2SO4 and Pt electrodes as reference and comparison electrodes in a standard three-electrode cell by extended cyclic voltammetry (CV, -1.0～1.0 V, relative to the reversible hydrogen electrode). ]
[The reduction peak and specific capacitance at -0.75 V were tested by X-ray photoelectron spectroscopy (XPS) to detect and control the reduction degree of graphene oxide. ]
[Further, the graphene oxide was modified on a conductive glass substrate by electrochemical deposition, and then paired with a glassy carbon electrode in a 0.1 mol/L solution, and a 0～-0.1 V intensity scan was performed to obtain a thin film on the substrate. ]
[.]
The information was not very detailed, and even the electron microscope structure diagrams were missing, but it was enough for Xu Chuan to understand clearly how they did it.
I have to say that this is an unusually clever way to take a different approach.
Nowadays, the materials industry has been considering whether to use reducing agents or catalysts to reduce graphene oxide and prepare graphene.
Although microwave reduction, hydrothermal reduction, catalytic reduction and other methods have been studied, these are actually not free from the limitations of reducing agents and catalysts.
And 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, in the process of reduction, he has no influence from other external additives.
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