Structure and capacitive properties of porous nanocrystalline VN produced by NH3 reduction of V2O5

Vanadium nitride (VN) is currently one of the most promising materials for electrodes of supercapacitors. The structure and electrochemical properties of VN synthesized by temperature-programmed NH₃ reduction of V₂O₅ are analyzed in this paper. Vanadium nitride produced via this route has distinctive structural characteristics. VN mimics the shape of the initial V₂O₅ precursor indicating a pronounced direct attachment of nitride grains. The particles have domains of grains with a preferential orientation (texture). The large volume of pores in VN is represented by the range of 15−110 nm. VN demonstrates capacitive properties in three different types of aqueous electrolytes, 1 M KOH, 1 M H₂SO₄, and 3 M NaCl. The material has an acceptable rate capability in all electrolytes, showing about 80% of its maximal capacitance at a current load of 1 A/g in galvanostatic charging/discharging experiments. The capacitance of 186 F/g is observed in 1 M KOH electrolyte at 1 A/g. The previously reported negative effect of material loading on the capacitance is significantly suppressed. The observed electrochemical characteristics related to the application of this material in supercapacitors can be correlated with the crystalline structure of the nitride and the composition of its surface layer.

Design and simulation of a high isolation RF MEMS shunt capacitive switch for C-K band

This paper presents a wide band RF MEMS capacitive switch. The LC resonant frequency is reduced from mm wave to X band frequencies at down-state by using a meander type membrane, with the frequency band is being increased by adding two short high impedance lines at both ends of coplanar waveguide (CPW). Moreover, this acts as T-match circuit in up-state position and improves the matching. Simulation results demonstrate that the capacitance ratio reduces from 50 to 21.4, S21 and S11 are less than −10dB for the entire frequency band at down-state and up-state. Also, a comprehensive and complete electric model of the switch is proposed and simulation results agree well with the characteristics of the physical structure of the MEMS switch. Vpull-in and Vpull-out of this switch are 8.1V and 0.3V, respectively.