Microporous Carbon Electrodes Research Articles

On the molecular origin of supercapacitance in nanoporous carbon electrodes

Lightweight, low-cost supercapacitors with the capability of rapidly storing a large amount of electrical energy can contribute to meeting continuous energy demands and effectively levelling the cyclic nature of renewable energy sources. The excellent electrochemical performance of supercapacitors is due to a reversible ion adsorption in porous carbon electrodes. Recently, it was demonstrated that ions from the electrolyte could enter sub nanometre pores, greatly increasing the capacitance. However, the molecular mechanism of this enhancement remains poorly understood. Here we provide the first quantitative picture of the structure of an ionic liquid adsorbed inside realistically modelled microporous carbon electrodes. We show how the separation of the positive and negative ions occurs inside the porous disordered carbons, yielding much higher capacitance values (125 F g(-1)) than with simpler electrode geometries. The proposed mechanism opens the door for the design of materials with improved energy storage capabilities. It also sheds new light on situations where ion adsorption in porous structures or membranes plays a role.

Highly stable performance of supercapacitors using microporous carbon derived from phenol–melamine–formaldehyde resin

A series of microporous carbons were prepared by simple carbonization and activation of phenol–melamine–formaldehyde resin. The morphology, surface area, and elemental composition of the samples were investigated by scanning electron microscope, Brunauer–Emmett–Teller measurement, Raman spectra, and elemental analysis, respectively. Electrochemical characteristics were evaluated by cyclic voltammograms, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements in 6.0 mol L−1 KOH. The microporous carbon activated by KOH presented a high specific capacitance of 202 F g−1 at a scan rate of 2 mV s−1. Furthermore, the KOH-activated microporous carbon electrode exhibited durable operation, the total loss of capacitance after 20,000 cycles is 2% at a current density of 500 mA g−1. The good electrochemical performance of the activated carbon was ascribed to well-developed micropores, high surface area, larger pore volume as well as oxygen groups.

In Situ Studies of Ion Transport in Microporous Supercapacitor Electrodes at Ultralow Temperatures

AbstractThe ability to quickly store and deliver a significant amount of electrical energy at ultralow temperatures is critical for the energy‐efficient operation of high altitude aircraft and spacecraft, exploration of natural resources in polar regions and extreme altitudes, and astronomical observatories exposed to ultralow temperatures. Commercial high‐power electrochemical capacitors fail to operate at temperatures below –40 °C. According to conventional wisdom, mesoporous electrochemical capacitor electrodes with pores large enough to accommodate fully solvated ions are needed for sufficiently rapid ion transport at lower temperatures. It is demonstrated that strictly microporous carbon electrodes with much higher volumetric capacitance can be efficiently used at temperatures as low as –70 °C. The critical parameters, with respect to electrolyte properties and electrode porosity and microstructure, needed for achieving both rapid ion transport and efficient ion electroadsorption in porous carbons are discussed. As an example, the fabrication of an electrochemical capacitor with an outstanding performance at temperatures as low as –60 and –70 °C is demonstrated. At such low temperatures the capacitance of the synthesized electrodes is up to 123 F g−1 (≈76 F cm−3), which is 50–100% higher than that of the most common commercial electrochemical capacitor electrode at room temperature. At –60 °C selected cells based on ≈0.2 mm electrodes exhibited characteristic charge–discharge time constants of less than 9 s, which is faster than the majority of commercial devices at room temperature. The achieved combination of high energy and power densities at such ultralow temperatures is unprecedented and extremely promising for the advancement of energy storage systems.

Computational modeling of discharge of a lithium battery with a microporous carbon electrode

Galvanostatic discharge of a model lithium cell with a microporous carbon electrode is modeled. Predictions of the model without account for the electric field and with account for electrostatic interaction between the carbon electrode particles were compared. A certain difference was observed.

Comparison of Electrospun and Commercially Available Separator Materials for Supercapacitors

Supercapacitors based on two ideally polarizable microporous carbide-derived carbon electrodes and different mesoporous electrospun and commercially available separators in acetonitrile as the solvent for the 1.0 M (C2H5)3CH3NBF4 electrolyte have been completed and tested by cyclic voltammetry and electrochemical impedance methods. The limits of ideal polarizability, low-frequency limiting capacitance and series resistance, time constant, complex power components and other characteristics have been established. Influence of the separator chemical composition, thickness, density, specific surface area, total pore volume and pore size distribution on the slope of the cyclic voltammetry curves at higher potential scan rates v {greater than or equal to} 10 mV s 1 has been established explained by the different specific conductivity of ions in mesoporous separator.

Modelling of cycling of lithium battery with microporous carbon electrode

Modelling of cycling of lithium battery with microporous carbon electrode

4855253 Test method for random defects in electronic microstructures

Two types of patterns were achieved on the surface of NR211 membranes: holes and knolls. These patterns were produced on only one side of the membrane at the cathode. For equivalent specific surfaces, these two membrane patterning morphologies were tested in fuel cell conditions with very low platinum loading (30 μg/cm2). Catalyst loading was achieved by magnetron plasma deposition either on the microporous carbon electrode or directly on the patterned membrane. The fuel cell performances in dry conditions were found to be highly dependent on the morphology of the membrane surface. Results showed that the knoll morphology gave better fuel cell performances than the hole morphology. For the knoll morphology the current density increased by a factor of 1.78 at 0.7 V versus a pristine membrane, whereas the hole morphology appeared in some cases to deteriorate the fuel cell performances, despite an increase in the specific surface by a factor of 1.87 versus a pristine membrane. The concepts of top level (extreme surface of the patterned membranes) and bottom level (the pattern base) were introduced to highlight the phenomena of micro water management on the areas of the micro-patterns which act on the local conductivity of the protonic membranes. These results suggest that it is necessary to choose the morphology of the patterns very carefully before simply increasing the specific surface of protonic membranes.