Capacitance Of Electrochemical Double Layer Capacitors Research Articles

Applying machine learning to understand the properties of biomass carbon materials in supercapacitors

Carbon is a fundamental material in developing electrochemical double-layer capacitors (EDLCs), also known as supercapacitors. Many studies have proven the impact of various carbon material properties, such as surface area, pore volume, and chemical surface composition, on the specific capacitance of supercapacitors (EDLCs). However, research endeavors to comprehensively evaluate the contribution of these material properties in correlation with experimental parameters, such as electrolyte concentration, voltage window, and current density, are scarce. This study aimed to employ machine learning algorithms to comprehend the interdependence between the properties of biomass-based carbon and the aforementioned experimental parameters with the capacitance of EDLCs. Four models of the machine learning algorithms were utilized in this study, including linear regression (LR), M5-Rules, Random Tree (RT), and Multi-Layer Perceptron (MLP), to determine the most suitable algorithm for analyzing and predicting the capacitance of EDLCs. The results revealed that the MLP model exhibited the highest determination correlation coefficient (R) of 0.871 with a Mean Absolute Error (MAE) of 45.069 F/g. Besides, the study utilized a machine learning correlation attribute model and observed that the supercapacitor’s surface area and pore volume demonstrated significant correlations with the same correlation ratio of 0.4. In conclusion, these findings emphasize the importance of considering surface area and pore volume in developing and optimizing supercapacitors. Finally, this study adds knowledge in supercapacitors and provides valuable insights for designing and developing high-performance energy storage devices.

Effect of ion charges on the electric double layer capacitance of activated carbon in aqueous electrolyte systems

Abstract Carbon based electrochemical double layer capacitors (EDLCs) are known for high power density, but their energy density is limited due to surface characteristics of the electrode materials as well as the size and charge of the ions used in the electrolyte. Therefore, considering the current demand for enhanced energy density devices, we investigated the use of multivalent electrolytes to increase the capacitance of activated carbon (AC) based EDLCs. As part of these studies, we examined the effect of the charge of the multivalent ions on the capacitive behavior of microporous AC electrodes and compared with the univalent Li + system. We performed impedance and cyclic voltammetry measurements on AC electrodes in a symmetric two electrode configuration to determine the impedance and capacitance with respect to varying charge and concentration of the ions in the aqueous nitrate electrolytes. These studies clearly demonstrated an increased capacitance with Mg 2+ and Al 3+ implying the possible effects of ion mobility and electrolyte conductivity in addition to the multivalent charge. These preliminary observations clearly point to the importance of selection of electrolyte ions with more charge, conductivity, and suitable size with respect to the pore size of the electrodes in order to increase the capacitance of EDLCs.

Tetramethylammonium tetrafluoroborate: The smallest quaternary ammonium tetrafluoroborate salt for use in electrochemical double layer capacitors

Abstract Tetramethylammonium (TMA) ion is the smallest quaternary ammonium ion (QAI) that can be used in electrochemical double layer capacitor (EDLC) applications. Small ions improve the capacitance of EDLCs by increasing the adsorbed ionic density. Herein, we first report the utilization of TMA BF 4 in EDLCs and the properties of the smallest QAI are investigated. However, because of the poor solubility of TMA BF 4 , it must be combined with another salt, forming a binary-salt electrolyte. In this study, the maximum TMA BF 4 concentration used was 5 mol%. These binary salt mixtures contain a conventional electrolyte salt such as tetraethylammonium BF 4 , trimethylethylammonium BF 4 , or spiro-bipyrrolidinium BF 4 . In addition, 4–5 mol% TMA BF 4 was added to the conventional salt solution and a binary-salt electrolyte was obtained, leading to 12–13% increase in the capacitance compared to that of a 100 mol% conventional electrolyte at 10 A g −1 . This work proposes a new method to improve the performance of EDLCs by using binary-salt electrolytes.

Ionic Liquids as Electrolytes for Electrochemical Double-Layer Capacitors: Structures that Optimize Specific Energy.

Key parameters that influence the specific energy of electrochemical double-layer capacitors (EDLCs) are the double-layer capacitance and the operating potential of the cell. The operating potential of the cell is generally limited by the electrochemical window of the electrolyte solution, that is, the range of applied voltages within which the electrolyte or solvent is not reduced or oxidized. Ionic liquids are of interest as electrolytes for EDLCs because they offer relatively wide potential windows. Here, we provide a systematic study of the influence of the physical properties of ionic liquid electrolytes on the electrochemical stability and electrochemical performance (double-layer capacitance, specific energy) of EDLCs that employ a mesoporous carbon model electrode with uniform, highly interconnected mesopores (3DOm carbon). Several ionic liquids with structurally diverse anions (tetrafluoroborate, trifluoromethanesulfonate, trifluoromethanesulfonimide) and cations (imidazolium, ammonium, pyridinium, piperidinium, and pyrrolidinium) were investigated. We show that the cation size has a significant effect on the electrolyte viscosity and conductivity, as well as the capacitance of EDLCs. Imidazolium- and pyridinium-based ionic liquids provide the highest cell capacitance, and ammonium-based ionic liquids offer potential windows much larger than imidazolium and pyridinium ionic liquids. Increasing the chain length of the alkyl substituents in 1-alkyl-3-methylimidazolium trifluoromethanesulfonimide does not widen the potential window of the ionic liquid. We identified the ionic liquids that maximize the specific energies of EDLCs through the combined effects of their potential windows and the double-layer capacitance. The highest specific energies are obtained with ionic liquid electrolytes that possess moderate electrochemical stability, small ionic volumes, low viscosity, and hence high conductivity, the best performing ionic liquid tested being 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

Tetraethylammonium difluoro(oxalato)borate as electrolyte salt for electrochemical double-layer capacitors

Difluoro(oxalato)borate (ODFB−) is a less symmetric borate anion, which makes it possible to increase the solubility of tetraethylammonium (TEA+) salt in propylene carbonate (PC) and improve the capacitance of electrochemical double-layer capacitors (EDLCs). The use of TEAODFB with PC solvent in EDLCs was investigated in the paper. The results show that TEAODFB has good solubility in PC, and the conductivity is comparable to TEABF4/PC electrolyte. When the molar concentration of TEAODFB reaches to 1.6M, the TEAODFB/PC electrolyte has superior conductivity of 14.46mScm−1 and good capacitor characteristics. Despite the less accessible to the electrode and low energy density was achieved, the specific capacitance of 1.6M TEAODFB/PC electrolyte is 21.4Fg−1 at 1Ag−1, and the energy density and power density were comparable to 1M TEABF4/PC electrolyte at 1–5Ag−1. Temperature characteristic was also tested by 3.3F circular capacitors from −40 to 60°C, the result demonstrates that capacitors using 1.6M TEAODFB/PC electrolyte show much higher capacitance and energy density at the investigated temperatures, and the discharge capacitance of capacitors using 1.6M TEAODFB/PC electrolyte varies with the temperature less than that of 1M TEABF4/PC electrolyte.

Preparation and Characterization of ACs/TiO2 Composite Electrodes for Improving the Specific Capacitance of Electrochemical Double-Layer Capacitors

In this work, the energy storage composite electrodes were prepared by mixing activated carbons (ACs) modified with a nanosize titanium oxide (TiO2) through a means of ultrasonic vibration in ethanol solution for 30 min. We examined the cyclic voltammetry of the composite electrodes in an aqueous electrolyte, 1 M H2SO4. It was found that the specific capacitance of the composite electrodes measured in a range of 0-0.8 V was increased from 100 to 155 F/g compared to carbon electrodes comprised of activated carbon only. This was attributed to a reduction of polarization of the ACs modified by nanosized TiO2.

Preparation and Characterization of Activated Carbon Nanofiber Webs Containing Multiwalled Carbon Nanotubes by Electrospinning

Electrochemical double layer capacitors (EDLCs) are promising high power energy sources for many different applications where high power density, high cycle efficiency and long cycle life are needed. However, because the energy density of EDLCs is small compared to that of rechargeable batteries one needs to increase the capacitance of EDLCs. The nanofiber diameters range from 50 nm to 400 nm, depending on the concentration of polymer solution types, tip-to-collector distance, applied voltage, and viscosity of the solution. The main advantage of the electrospinning process is that it is a simple means to prepare continuous fibers with unusually large surface to volume ratios and pore structure surfaces. So, feature of nanofiber webs are the high specific surface area developed by creating pores on the nanofiber surface. In this work, the multiwalled carbon nanotubes embedded polyacrylonitrile solutions in N,N-dimethylformamide (DMF) were electrospun to be webs consisting of 350 nm ultrafine nanofibers, which were used to produce a series of activated carbon nanofibers with developed mesoporosity and high electrical conductivity through stabilization, carbonization-activation processes.