Karistusseadustiku § 394 lg 1 p 3 karistatavusala määratlemine

https://www.ester.ee/record=b545151

EDLC performance of carbide-derived carbons in aprotic and acidic electrolytes

This study shows that carbide-derived carbons (CDCs) with average pore size distributions around 0.9–1 nm and effective surface areas of 1300–1400 m2 g−1 provide electrochemical double-layer capacitors with high performances in both aqueous (2M H2SO4) and aprotic (1M (C2H5)4NBF4 in acetonitrile) electrolytes. In the acidic electrolytic solution, the gravimetric capacitance at low current density (1 mA cm−2) can exceed 200 F g−1, whereas the volumetric capacitance reaches 90 F cm−3. In the aprotic electrolyte they reach 150 F g−1 and 60 F cm−3. A detailed comparison of the capacitive behaviour of CDCs at high current density (up to 100 mA cm−2) with other microporous and mesoporous carbons indicates better rate capabilities for the present materials in both electrolytes. This is due to the high surface area, the accessible porosity and the relatively low oxygen content. It also appears that the surface-related capacitances of the present CDCs in the aprotic electrolyte are in line with other carbons and show no anomalous behaviour

EDLC performance of carbide-derived carbons in aprotic and acidic electrolytes

6 pages, 6 figures, 2 tables.-- Printed version published Oct 15, 2008.This study shows that carbide-derived carbons (CDCs) with average pore size distributions around 0.9–1 nm and effective surface areas of 1300–1400 m2 g−1 provide electrochemical double-layer capacitors with high performances in both aqueous (2M H2SO4) and aprotic (1M (C2H5)4 NBF4 in acetonitrile) electrolytes.In the acidic electrolytic solution, the gravimetric capacitance at low current density (1 mA cm−2) can exceed 200 F g−1, whereas the volumetric capacitance reaches 90 F cm−3. In the aprotic electrolyte they reach 150 F g−1 and 60 F cm−3.A detailed comparison of the capacitive behaviour of CDCs at high current density (up to 100 mA cm−2) with other microporous and mesoporous carbons indicates better rate capabilities for the present materials in both electrolytes. This is due to the high surface area, the accessible porosity and the relatively low oxygen content.It also appears that the surface-related capacitances of the present CDCs in the aprotic electrolyte are in line with other carbons and show no anomalous behaviour.Peer reviewe

Partial Oxidation to Extend the Lifetime of Nanoporous Carbon in an Ultracapacitor with Li₂SO₄ Electrolyte

A TiC-derived carbon (CDC) and its partially oxidized derivative (ox-red-CDC), oxidized by a modified Hummers method, were studied as promising electrode materials for electrochemical energy storage. To evaluate the electrochemical properties of the carbon materials, cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy measurements were performed in 1 M Li2SO4 using 2- and 3-electrode cells. A partially oxidized surface was shown to improve the capacitance and electrochemical stability of a nanoporous CDC at positive potential values. The respective anodic capacitance of 80 F cm−3 reveals a 15% improvement over the non-oxidized CDC. At negative potential values, the capacitance of two carbon materials is almost equal, 97 vs. 93 F cm−3, for the non-oxidized and partially oxidized CDC materials, respectively. An asymmetric 2-electrode ultracapacitor containing ox-red-CDC as the anode and pristine CDC as the cathode demonstrated an excellent cycle life. The temporary repolarization of the 2-electrode cell after thousands of charge–discharge cycles increased the capacitance and improved the cycling characteristics, likely due to regeneration and cleaning of the electrode surface

Electrochemical Evaluation of Directly Electrospun Carbide-Derived Carbon-Based Electrodes in Different Nonaqueous Electrolytes for Energy Storage Applications

This study focuses on the electrochemical behavior of thin-layer fibrous carbide-derived carbon (CDC) electrospun electrodes in commercial and research and development stage organic-solvent and ionic liquid (IL) based electrolytes. The majority of earlier published works stated various electrolytes with asymmetric cells of powder-based pressure-rolled (PTFE), or slurry-cast electrodes, were significantly different from the presented CDC-based fibrous spun electrodes. The benefits of the fibrous structure are relatively low thickness (20 µm), flexibility and mechanical durability. Thin-layered durable electrode materials are gaining more interest and importance in mechanically more demanding applications such as the space industry and in wearable devices, and need to achieve a targeted balance between mechanical, electrical and electrochemical properties. The existing commercial electrode technologies lack compatibility in such applications due to their limited mechanical properties and high cost. The test results showed that the widest potential window dU ≤ 3.5 V was achieved in 1.5 M 1-ethyl-3-methylimidazoliumbis(trifluoromethyl-sulfonyl)imide (EMIm-TFSI) solution in acetonitrile (ACN). Gravimetric capacitance reached 105.6 F g−1 for the positively charged electrode. Cycle-life results revealed stable material capacitance and resistance over 3000 cycles

Nanoporous Carbide-Derived Carbon Material-Based Linear Actuators

Devices using electroactive polymer-supported carbon material can be exploited as alternatives to conventional electromechanical actuators in applications where electromechanical actuators have some serious deficiencies. One of the numerous examples is precise microactuators. In this paper, we show for first time the dilatometric effect in nanocomposite material actuators containing carbide-derived carbon (CDC) and polytetrafluoroetylene polymer (PTFE). Transducers based on high surface area carbide-derived carbon electrode materials are suitable for short range displacement applications, because of the proportional actuation response to the charge inserted, and high Coulombic efficiency due to the EDL capacitance. The material is capable of developing stresses in the range of tens of N cm-2. The area of an actuator can be dozens of cm2, which means that forces above 100 N are achievable. The actuation mechanism is based on the interactions between the high-surface carbon and the ions of the electrolyte. Electrochemical evaluations of the four different actuators with linear (longitudinal) action response are described. The actuator electrodes were made from two types of nanoporous TiC-derived carbons with surface area (SA) of 1150 m2 g-1 and 1470 m2 g-1, respectively. Two kinds of electrolytes were used in actuators: 1.0 M tetraethylammonium tetrafluoroborate (TEABF4) solution in propylene carbonate and pure ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMITf). It was found that CDC based actuators exhibit a linear movement of about 1% in the voltage range of 0.8 V to 3.0 V at DC. The actuators with EMITf electrolyte had about 70% larger movement compared to the specimen with TEABF4 electrolyte

Quantitative Nano-Structure–Property Relationships for the Nanoporous Carbon: Predicting the Performance of Energy Storage Materials

Nanoporous carbon-based energy storage is a fast-growing research field thanks to high energy densities of carbon electrodes with nanoporous amorphous texture. To support the developments on electrical double-layer based ultracapacitors, it is necessary to improve understanding about relationships between the porous structure and energy storage behavior of carbon materials. This can be facilitated by the analysis of complex data sets and the development of corresponding descriptive and predictive models. Related to that, this work presents an in silico regression model to predict the suitability of various carbon materials for energy storage, thus being probably the first time a quantitative nanostructure–property relationship (QnSPR) approach is applied to the nanoporous carbon materials. With this study, which is based on the experimental data of 100 carbide-derived carbon materials, it has been shown that the electrical double layer capacitance of carbon electrode in a nonaqueous electrolyte can be predicted using experimentally determined specific surface area, a volume of certain pore size fraction of carbon and a bulk density of carbon electrode. The three-parameter QnSPR model for volumetric cathodic capacitance of carbon in triethylmethylammonium tetrafluoroborate/propylene carbonate electrolyte, <i>C</i>_V,NEG = <i>f</i>(<i>S</i>_BET, <i>V</i>_{<i>d</i><1.14}, <i>D</i>_el), comprising the above-mentioned parameters and characterized by <i>R</i>² = 0.94 and <i>s</i>² = 8.7, confirms the important role of carbon pore size for the double layer capacitance. It was shown that carbon pores with a size below 1.1 nm have the most significance for achieving high energy densities in the nonaqueous electrochemical systems studied. Putting the results of this research into wider perspective, it has been shown that the QnSPR approach provides a useful tool for describing and predicting the variable performance-related physical properties of nanoporous carbon and nanomaterial properties in general. The models are available in the QsarDB repository (http://dx.doi.org/10.15152/QDB.205)