This paper aims at finding the experimentally controllable variables of solvent for the electric double layer capacitance obtained at two parallel platinum wire electrodes in the polarized potential domain. The equivalent circuit used is the frequency-dependent double layer impedance in series with solution resistance. The evaluated capacitance shows no systematic relation with the dielectric constants, viscosity, boiling temperatures, or dipole moments of the solvents but is proportional to the inverse of the lengths of field-oriented molecules. The proportionality indicates common saturated dielectric constants, 6, of 13 solvents. The variables controlling the capacitance are the saturated dielectric constants and the lengths of solvent molecules along the dipole.

Nowadays, transition-metal oxides are regarded as the most potential materials for the supercapacitor and electrocatalyst. However, the poor electrical conductivity and insufficient active sites limited their development in various fields. Herein, we report the method of phosphorous-doped NiCo 2 O 4 (named as P-NCO) prepared by the two-step strategy: the NiCo 2 O 4 nanostructure is grown on the nickel foams by hydrothermal treatment and subsequently phosphatized in a tube furnace. Successfully, the rich oxygen vacancies and the P element introduced into the NiCo 2 O 4 structure obviously improve the electrical conductivity, and the resulting P-NCO NWs/NF material shows an ultrahigh specific capacitance of 2747.8 F g −1 at 1 A g −1 and a prominent rate performance (maintain 50% at 100 A g −1 ). Furthermore, the assembled P-NCO NWs/NF//RGO asymmetric supercapacitor has an energy density of 28.2 W h kg −1 even at a high power density of 7750.35 W kg −1 . After 10,000 cycles, the capacitance still also has an 88.48% retention rate. As an electrocatalyst, P-NCO NWs/NF has an excellent hydrogen evolution reaction (55 mV at 10 mA cm −2 ) and oxygen evolution reaction (300 mV at 10 mA cm −2 ) activities in 1 M KOH solution. This study provides an effective strategy to prepare multifunctional materials.

The behavior of electric double layers at polarized interfaces in KC1 solutions is revisited in order to examine properties of the constant phase element (CPE). We pay attention specifically to frequency dependence of both the capacitance and the resistance. Two parallel platinum wires immersed in solution are used as insulator-free * C orresponding author, phone +81

The aim of this study was to prepare manganese dioxide with different crystal forms through hydrothermal

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