Researchers have prepared a carbon aerogel with a 3D honeycomb structure for the first time. Image source: Peng Xinwen Research Group of South China University of Technology
At the State Key Laboratory of Pulp and Paper Engineering at South China University of Technology, researchers are carefully removing a piece of black material from the transparent plastic shell. Its texture looks like a burnt cake, but the mass per cubic centimeter is only a few milligrams. When a person walks by, the small crumbs produced when cutting the "cake" will float in the air for a while, and then slowly fall.
This dark "cake" is actually a carbon aerogel newly prepared by the team of laboratory members and professor Peng Xinwen of the School of Light Industry Science and Engineering of South China University of Technology. When applied to zinc-air batteries, at a high current density of 20 milliamperes per cubic centimeter, the battery's specific capacity can reach 648 milliamperes/g. Related results have been published in "Advanced Materials" recently.
Peng Xinwen told China Science Daily that the skeleton of this carbon aerogel is derived from the fibers in the paper. At the micro level, the researchers designed and adjusted the structure of the wood fiber used in papermaking, and found a new world for this ancient biomass.
Application of Biomass Carbon Aerogel Transboundary Battery
The research direction of Peng Xinwen's group is high-performance biomass materials and paper-based materials. Paper-based materials are biomass such as wood and straw. Their main components are cellulose and lignin. By controlling the fiber diameter at the nanometer level, nanocellulose with excellent flexibility, aspect ratio and mechanical properties can be obtained. Alkenes, one-dimensional carbon nanotubes, etc., are used as basic building materials by researchers.
In the research published this month, the carbon aerogel developed by Peng Xinwen's group is based on nanocellulose. Wu Kunze, the first author of the thesis and a master's student in the research group, told China Science Daily that carbon aerogel is also called carbon foam because of its soft and porous properties. When the carbon foam is combined with the graphene material, it shows superior basic mechanical properties. "It has high mechanical strength and good water dispersibility."
In fact, the research group has focused on carbon aerogel research for several years. At the beginning, Peng Xinwen and others used this material to prepare a flexible pressure sensor, which was mounted on the electronic device of a wearable device to sensitively monitor electrochemical signals. During the preparation process, the research team found that after doping with nitrogen and metals, the carbon aerogel has catalytic activity and can be used as a dual-functional catalyst for oxygen reduction and oxygen precipitation.
"This is actually the working principle of fuel cells." Peng Xinwen said, combining her previous research background in the field of fuel cells, she and other members of the research team began to think about how to design carbon aerogels as negative electrodes for air batteries.
"Carbon aerogel with pore structure has good electrical conductivity and mechanical stability. Adjusting it and giving it some catalytic activity can make this material not only act as a catalyst, but also play a role as a conductive carrier. Role." Wu Kunze said.
Since 2013, many research teams in this field have been working on the research and development of carbon aerogels, which have a porosity of 80% to 99% with excellent thermal stability and conductivity. Carbon aerogels with wavy sheet structure and biomimetic structure came out during this period, and their preparation methods and performance are also continuously improved.
But before this, there was no research report on the use of cellulose carbon aerogel for air electrodes. To achieve this goal, it means that carbon aerogels must maintain high porosity and strong mechanical properties, as well as exhibit stable and efficient electrocatalytic properties.
Three birds with one stone and freezing casting make the material "obedient"
In the past, methods for preparing carbon aerogels included hydrothermal methods, chemical vapor deposition methods, template methods, etc., but they often failed to strike a balance between controllability and low cost. For this reason, researchers have focused on the old method in the field of ceramic manufacturing-the freezing casting method.
"Carbon aerogel must have a rich pore structure, and the freezing casting method can guarantee this. Moreover, it is very economical. Biomass materials such as nanocellulose can also match the freezing conditions." Wu Kunze introduced.
In the experiment, the research team used nanocellulose and graphene as the carbon skeleton, and by controlling the temperature gradient during the freezing process, the aqueous solution used as the substrate was condensed into ice crystals in a fixed direction. The formed ice crystal substrate and the skeleton overlap each other like a layered cake. At this time, the freeze-drying process is carried out, the ice crystals sublime and disappear, and then the material is carbonized, and finally a carbon aerogel with a layer spacing and a stacked structure is born. .
With high porosity and mechanical properties guaranteed, where does the catalytic performance of carbon aerogel come from? In the preliminary preparations, the researchers will add a coupling of ferric chloride and phytic acid to the precursor solution, and at the same time add glucosamine as a small molecule nitrogen source, so as to achieve the loading of iron metal and the doping modification of nitrogen and phosphorus to ensure carbon condensation Glue has catalytic properties.
"After being doped with nitrogen, phosphorus, and iron, the electrode made of carbon aerogel can complete the catalytic circuit of oxygen precipitation and oxygen reduction by itself, forming an electronic path. After a large number of experiments and verifications with collaborators, they found This is actually a very good electrocatalyst." Peng Xinwen told reporters.
So far, in fuel cells, catalysts made of precious metals such as platinum and ruthenium are mostly ground into powder, and then added to conductive supports such as carbon cloth and stainless steel mesh. "There is a problem in this process. If the powder is stacked too much, the conductive carrier will not stick, the catalyst will fall off during the reaction, causing the battery to die, and the catalyst will no longer work." Peng Xinwen explained that this will affect the battery. Work efficiency has a great impact.
But carbon aerogel breaks this existing routine and realizes "one stone with three birds"-it integrates the three functions of electrode, conductive carrier and catalyst, and the internal metal and carbon form a stable chemical bond, which can not only make the catalyst Play a stable role in your job without cracking the electrode layer.
Peng Xinwen said that it is not difficult to control this material. "If you have mastered a certain performance control technology, it is still very good."
Find the right power point to enter the homes of ordinary people
"This material has a 3D vertical honeycomb structure with inter-connected pores on the pipe wall, which is conducive to gas diffusion and electrolyte infiltration, and has good flexibility and excellent electrochemical energy storage performance." Professor of Dalian University of Technology, Cellulose and Ke Sun Runcang, the winner of the "Anselm Payne Award", the highest award in the field of renewable resource materials, mentioned in his comments that the future work is expected to provide high-performance electrode materials for flexible electronic devices, and for the conversion of biomass into carbon materials, electrochemical storage Can apply to provide new methods.
In Peng Xinwen's view, powering large equipment such as trams and generators is not the ultimate destination of all batteries. Based on the characteristics of low cost and environmental friendliness, batteries made of biomass materials can shine in flexible electronic devices and incorporate various details in daily life.
"In the future, we will continue to reduce the thickness of the material for wearable devices such as watches that can be charged and discharged." Peng Xinwen pointed out that since such devices have no stringent requirements for battery life, "as long as the cost performance is appropriate, we can develop it." . In the future, electrodes made of replaceable and inexpensive biomass carbon materials will eventually move toward industrial applications.
Light, thin, and soft, carbon aerogels based on nanocellulose seem to be mild and have a "low" sense of existence, but they have been given many possibilities by researchers. In the future, nanocellulose will not only play its strengths in the field of functional papermaking, but the films and particles made from it can also be used in fields such as energy, biomedicine, and molecular imaging.
Just like a small piece of carbon aerogel, even if it first floats in the air, it will eventually land. In Peng Xinwen's view, the same is true for scientific research. "You can't fly high in the cloud. In the end, you have to land and apply. This is our original intention for research." (â– Ren Fangyan, our reporter's trainee reporter)
Alumina ceramics are ceramic materials based on alumina (Al2O3) for thick film integrated circuits. Alumina ceramics have good conductivity, mechanical strength and high temperature resistance. It should be noted that ultrasonic cleaning is required. Alumina ceramics is a versatile ceramic. Because of its superior performance, it has been widely used in modern society, satisfying the needs of daily use and special performance.The high-purity alumina ceramics have a Al2O3 content of 99.9% or more. Since the sintering temperature is as high as 1650-1990 ° C and the transmission wavelength is 1 to 6 μm, the molten glass is generally used to replace the platinum crucible; Sexual and alkali-resistant metal corrosion is used as a sodium lamp; it can be used as an integrated circuit substrate and high-frequency insulation material in the electronics industry.
Alumina Ceramics,Alumina Ceramics Parts,Wear Resistant Alumina Ceramic
Dongguan Haikun New Material Co., Ltd. , https://www.nitrideceramic.com