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Abstract We apply a combination of experimental measurements and molecular dynamic (MD) simulations to describe imidazolium ionic liquids with porous carbon electrode. On the experiment's side, electrochemical measurements are conducted on two types of porous carbon electrodes prepared from different pore size distributions. The general trend of variations for impedance are identified at various temperatures and electrode geometries in Nyquist plots. On the simulation's side, fundamental geometries including slit and cylindrical pores are modeled to determine the ions' behaviours during charging and discharging process. By examining the local charges variations, the electrode charging or polarization are correlated with ion dynamics or relaxation, particularly in the vicinity of electrode. In one-to-one correspondence to experiments, linear segment of impedance for individual pores gives rise to the constant phase element in fitting of porous electrode's equivalent circuit. Our MD simulations explored the path of implementing the techniques of cyclic voltammetry and electrochemical impedance spectroscopy. [ABSTRACT FROM AUTHOR]

Reasonable design of electrode materials with excellent capacitance performance is essential for the construction of high-energy–density supercapacitors. In this work, we synthesized three SmMn2O5 nanocrystals with different morphologies through a simple one-step hydrothermal method, which are SmMn2O5-NSs, SmMn2O5-NRs, and SmMn2O5-NPs. Compared with SmMn2O5-NPs and SmMn2O5-NRs, SmMn2O5-NSs exhibit excellent electrochemical performance of capacitors. At a scanning speed of 1 mV s−1, the specific capacity of the SmMn2O5-NSs reaches 334.25 F g−1, which is much higher than the 52 F g−1 and 42.84 F g−1 of SmMn2O5-NRs and SmMn2O5-NPs, respectively. Meanwhile, SmMn2O5-NSs have a higher specific surface area and more octahedral Mn4+. The specific surface area increases the exchange rate of ions and protons between the material and the electrolyte, and more Mn4+ can provide more Mn–O bonds during the reaction. These results indicate that controlling the morphology of SmMn2O5 nanocrystals by changing hydrothermal reaction conditions is an effective way to construct high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

α-Form Co xNi1- x hydroxides with different Co/Ni ratios were synthesized by a chemical co-precipitation method under mild conditions. The effects of Co/Ni ratio on the structure, morphology, and supercapacitive properties of α-form Co xNi1- x hydroxides were investigated in detail. α-Form Co xNi1- x hydroxides had structures similar to those of hydrotalcite and α-Co(OH)2, and they exhibited better electrochemical performance than α-Co(OH)2 on testing by XRD, FTIR, and electrochemical performance (when x ≠ 0). The highest specific capacitance at 1 A g-1 for α-form Co xNi1- x hydroxides (for x = 0.2) is 1696.7 F g-1. An asymmetric supercapacitor packaged with Co0.6Ni0.4 hydroxide and activated carbon as positive and negative material, respectively, had an energy density of 23.5 Wh kg-1 at a power density of 412.5 W kg-1. [ABSTRACT FROM AUTHOR]

Traditional filtering capacitors suffer from low volumetric energy density (Ev), which hinders their integration in miniaturized electronics and their high‐frequency response ability to alternating current (AC). Here, a supercapacitor based on a carbon nano‐onion (CNO)‐graphene hybrid structure concurrently possessing high Ev and ultrahigh rate capability is reported for AC filtering. The hybrid structure is synthesized on etched nickel foil using preformed monodispersed nanocrystals through a chemical vapor deposition method. The supercapacitor device shows capacitive behavior independent of voltage scan rate up to 5000 V s−1 in both aqueous and organic electrolytes, which represents a record high among the reported filtering capacitors to date. It also exhibits a high Ev of 14.9 F V2 cm−3 at 120 Hz and 28.8 mWh cm−3 at a current density of 0.25 mA cm−2. Moreover, the supercapacitor is capable of filtering AC with different waveforms at high frequencies into direct current. The hybrid structure holds promise for applications in compact filtering units. The ultrafast ion transportation performance is enabled by the highly positive surface curvature of CNOs, hierarchical interconnection of CNO particles, and the covalent interfacial bonding between CNOs and graphene. [ABSTRACT FROM AUTHOR]

Supercapacitors: Ultrahigh-Rate Supercapacitor Based on Carbon Nano-Onion/Graphene Hybrid Structure toward Compact Alternating Current Filter (Adv. Keywords: alternating current filters; carbon onions; supercapacitors; ultrahigh rate capability EN alternating current filters carbon onions supercapacitors ultrahigh rate capability 1 1 1 11/19/20 20201117 NES 201117 In article number 2002132, Chenguang Zhang and co-workers report on an ultrahigh-rate supercapacitor fabricated based on a carbon onion/graphene hybrid structure for high-performance alternating current line filtering. Alternating current filters, carbon onions, supercapacitors, ultrahigh rate capability. [Extracted from the article]

Copper cobalt carbonate hydroxide (Cu-Co CH) microspheres were synthesized as a pseudocapacitive electrode material via a simple one-step hydrothermal method. Morphological characterization of the Cu-Co CH microspheres was carried out by scanning electron microscopy and transmission electron microscopy, showing their dandelion-like structure with the size approximately 4–7 μm. The crystalline structure, morphology and electrochemical performances of Cu-Co CH materials could be readily dominated by the molar ratio of Cu to Co. Among various stoichiometries of Cu-Co CHs, sample Cu 0.48 Co 1.52 CH delivered the highest specific capacitance of 397.3 F g − 1 at 1 A g − 1 with a good rate capability. Cu 0.48 Co 1.52 CH electrode material also exhibited a remarkably excellent cycling stability, ~ 99% of initial capacitance retention even after 10,000 charge/discharge cycles at 2 A g − 1 . An asymmetric energy storage device was assembled by using Cu 0.48 Co 1.52 CH as positive electrode and activated carbon as negative electrode in 2 M KOH electrolyte. The hybrid capacitor device could deliver an energy density of 26.3 Wh kg − 1 at a power density of 400.2 W kg − 1 , and remain 16.7 Wh kg − 1 at 8374.2 W kg − 1 . Meanwhile, it also showed amazing stability with ~ 99% capacity retention after 10,000 cycles. Based on the above results, Cu-Co CH microspheres possessed practical application as electrode materials for electrochemical capacitors due to their good structural stability in KOH electrolyte. [ABSTRACT FROM AUTHOR]