Ultrasonic Spraying Porous Carbon Felt Electrode
The key role and advantages of ultrasonic spraying in porous carbon felt electrodes
In the field of modern energy conversion and storage, electrodes play a vital role. They are the core area for realizing the mutual conversion of electrical energy and chemical energy. Taking liquid flow batteries as an example, in its reaction process, the active substances in the electrolyte complete the key electrochemical reaction by accepting or giving electrons at the electrode-electrolyte interface. The special space in the porous electrode cleverly couples the mass transfer of the electrolyte with the interfacial electrochemical reaction. When the electrolyte flows through the electrode driven by the pressure difference, it slowly penetrates into the pores of the porous electrode. At this time, the reaction ions reach the surface of the carbon fiber in the electrode by means of convection, diffusion and migration, and then undergo redox reactions. The products after the reaction are completed will return to the electrolyte solution through the process of desorption and diffusion.
During the continuous operation of the liquid flow battery, the three polarization phenomena caused by different depths inside the porous carbon felt electrode structure have a direct and critical impact on the performance of the liquid flow battery. The three polarizations are: first, ohmic polarization caused by solid and liquid phase resistance; second, concentration polarization caused by mass transfer processes such as diffusion and convection of electrolyte in pores; third, electrochemical polarization derived from electrochemical reactions on the surface of carbon felt. In-depth analysis shows that the transmission of ions and electrons in the electrolyte in the carbon felt directly determines the degree of ohmic polarization and concentration polarization; and the magnitude of electrochemical polarization mainly depends on the reversibility and activity of the electrode reaction on the carbon felt. It is worth noting that the conductivity and thickness of carbon felt have a great influence on ohmic polarization; the unique three-dimensional structure and lyophilicity of carbon felt are closely related to concentration polarization and are inseparable.
In order to achieve the goal of high transmission performance of electrolyte and active substances, we expect the electrode to have high porosity and permeability to ensure the smoothness of the macroscopic transmission channel. However, in actual operation, this often leads to a decrease in the specific surface area of the electrode, which restricts the construction of the electrode reaction interface and the improvement of electrochemical performance. It is clear that the macroscopic and microscopic three-dimensional structural characteristics and surface chemical properties of carbon felt electrodes have a complex relationship of mutual correlation and mutual restriction on the three polarizations. Therefore, the key point of developing high-performance electrodes is to deeply explain the intrinsic connection between material, electron, ion transmission and electrochemical reaction, and strive to break the strong correlation between various factors, so as to achieve the ultimate goal of synergistic optimization of spatial energy transfer and interfacial electrochemical reaction.
In the porous carbon felt electrode structure, there is a unique multi-level pore structure. Among them, the primary pore is composed of carbon fibers overlapped with each other, and its pore size is generally in the range of tens to hundreds of microns. Its main function is to provide channels for the flow and transmission of macroscopic electrolytes; the secondary pores are distributed on the surface of carbon fibers, and the pore size is usually tens to hundreds of nanometers, which is responsible for providing channels for the diffusion, migration and convection of electrolyte reaction ions on the electrode surface; the tertiary pores exist inside the secondary pores, with a pore size of only 1-2 nm. Its main function is to increase the specific surface area of the electrode and provide a key place for electrochemical reactions. By carefully developing macroscopic and microscopic ordered electrode structures, we can achieve effective regulation of battery polarization. From a macroscopic perspective, by adjusting the compression ratio of the electrode, cleverly constructing the flow field structure of the electrode, or changing the shape of the electrode, the transmission characteristics of the electrode macro-channel to the electrolyte can be significantly improved. At the microscopic level, constructing a single-layer electrode with a multi-level pore structure and a multi-layer electrode structure with a gradient distribution can not only increase the electrode specific surface area and effectively promote the electrochemical reaction, but also improve the diffusion of the electrolyte on the electrode surface, successfully breaking the strong correlation between the electrode specific surface area and the permeability.
Among the many technologies for optimizing the performance of porous carbon felt electrodes, ultrasonic spraying technology is gradually emerging, showing unique application value and significant advantages. Ultrasonic spraying technology uses high-frequency ultrasonic vibrations to atomize liquid into extremely fine and uniform droplets. When applied to porous carbon felt electrodes, first of all, it can achieve precise coating thickness control. Traditional spraying methods often make it difficult to ensure the uniformity of the coating, and are prone to local over-thickness or over-thinness. However, ultrasonic spraying technology can ensure that the coating is evenly covered on the surface of the carbon felt, and a coating of consistent thickness can be obtained on the surface of the primary, secondary or tertiary holes. This is of great significance for improving the surface chemical properties of the electrode, enhancing its lyophilicity and conductivity, and thus effectively reducing ohmic polarization and concentration polarization.
Secondly, ultrasonic spraying technology can effectively increase the specific surface area of the electrode. Because the tiny droplets it produces can penetrate into the multi-level pore structure of the carbon felt, especially the tertiary pores, additional reaction sites are formed in these pores, further increasing the specific surface area of the electrode. This provides more places for electrochemical reactions, greatly promotes the improvement of electrochemical polarization, and improves the reversibility and activity of electrode reactions on carbon felt.
Furthermore, ultrasonic spraying technology helps to optimize the microstructure of the electrode. It can finely modify the carbon felt without destroying its original macroscopic and microscopic structure. By controlling the spraying parameters, a specific microstructure can be formed on the surface and pores of the carbon felt. This structure is conducive to the transmission of the electrolyte in the electrode, further enhancing the transmission characteristics of the electrode to the electrolyte, breaking the restrictive relationship between the electrode structure characteristics, and improving the overall performance.
In summary, in the research and application of porous carbon felt electrodes, it is crucial to deeply understand the relationship between electrode structure and the three polarizations. Ultrasonic spraying technology, with its unique advantages in coating uniformity, increasing specific surface area and optimizing microstructure, provides a new and effective way for the development of high-performance porous carbon felt electrodes, and is expected to play a more important role in the future field of energy storage and conversion, and promote the continuous innovation and progress of related technologies.
About Cheersonic
Cheersonic is the leading developer and manufacturer of ultrasonic coating systems for applying precise, thin film coatings to protect, strengthen or smooth surfaces on parts and components for the microelectronics/electronics, alternative energy, medical and industrial markets, including specialized glass applications in construction and automotive.
Our coating solutions are environmentally-friendly, efficient and highly reliable, and enable dramatic reductions in overspray, savings in raw material, water and energy usage and provide improved process repeatability, transfer efficiency, high uniformity and reduced emissions.
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