This thesis, containing two main parts. In the first part which is contains three sections, different new nanocomposite were synthesiszed and characterized by different techniques. The potential application of the prepared nanocomposites as an electrode material of supercapacitors were investigated using cyclic voltammetry, galvanostatic chronopotentiometry and electrochemical impedance spectroscopy. In the first section, copper-bismuth mixed oxide (CuBi2O4) nanoparticles were supported on nanoporous stainless steel by a simple electrochemical deposition method and then was employed as a binder-free electrode for supercapacitor application. The results showed that the proposed electrode exhibited a maximum specific capacitance of 144 mAh g-1 or 647 F g-1 at a current density of 1.0 A g-1 in 6.0 mol L-1 KOH with excellent long-term cycling stability (80% capacitance remained after 500 charge-discharge cycles). In the second section polypyrrole/nickel-cobalt hexacyanoferrate (PPy/NiCoHCF) nanocomposite was synthesized using a fast and facile electrochemical approach on a low cost stainless steel substrate. The capacitive behavior of the nanocomposite was investigated in aqueous and non-aqueous electrolytes. The results show that incorporation of NiCoHCF improves the capacitance properties of PPy in both aqueous and non-aqueous media. Maximum capacitance of 529 F g–1 and 668 F g–1 at the current density of 1.0 Ag?1 are achieved for the proposed nanocomposite in aqueous and non-aqueous electrolytes, respectively using galvanostatic charge-discharge technique. Moreover, the nanocomposite shows high specific power density (5600 W kg–1) and high specific energy density (87 Wh kg–1) at a current density of 10 Ag–1. In the last section, a quaternary nanohybrid of graphene/polyaniline-benzimidazole grafted graphene/MnO2 was performed as an electrochemical supercapacitors anode. Combination of high surface area of graphene, the high electrical conductivity of polyaniline and good charge storage capacity of MnO2 lead to a new electrode material for supercapacitor application. The prepared nano hybrid electrode material exhibits surpassing electrochemical performance than graphene/polyaniline and graphene/MnO2 nanocomposites, including a high specific capacitance of 675 F g?1 or 150 mAh g?1 at a discharge current of 50 A g?1. The nanocomposite showed excellent rate capability (over 80% retention at 50 A g?1) and high cycling stability with less than 13% of capacitance fading after 2000 cycles of galvanostatic charge-discharge as well as a high columbic efficiency of 96% at a high discharge current of 50 A g?1. The obtained results reveal that the proposed nanocomposites would be good candidates for electrode materials of supercapacitors with high charge storage capacity, good stability and high columbic efficiency in the future. In the second part (containing two sections), porous silicon was synthesized by chemical etching method and characterized by different techniques. Then, Pd@PSi and Ni@PSi nanocomposites were prepared using a simple galvanic loading of Pd and Ni nanoparticles on the surface of porous silicon in fluoride ions solution. Finally, the prepared nanocomposites were used for construction of new electrochemical sensors. In the first section, Pd@PSi containing carbon nanotube modified carbon paste electrode was used for voltammetric determination of acetaminophen and codeine. The results showed that the combination of the electrocatalytic activity of Pd nanoparticles, high conductivity of carbon nanotubes and high surface area of porous silicon provide a new sensing surface for simultaneous determination of acetaminophen and codeine with wide linear ranges and good selectivity. Under the optimum conditions, the oxidation current responses of acetaminophen and codeine were linear in the concentration range of 1.0–700.0 µmol L–1. The detection limits of 0.4 and 0.3 µmol L–1 were achieved for acetaminophen and codeine, respectively. In the second section, Ni@PSi was used for electrocatalytic detection of glucose by carbon paste electrode. The results indicate that Ni@PSi/CPE is a promising candidate for routine analysis of glucose in real samples. Glucose could be measured in the range of 2.0–5000 µmol L–1 and with detection limit of 200 nmol L–1 using chronoamperometry technique. The excellent applicability of the proposed method for determination of glucose in human blood serum with good accuracy and reproducibility made Ni@PSi nanocomposite promising for the development of effective electrochemical non-enzymatic glucose sensor.