Unipolar Pulse Electrodeposition And Pseudocapacitor Performances Of Porous Composite Electrode

Supercapacitor is a new kind of energy storage device which is mainly composed of electrode materials, electrolyte, separator and current collector, pseudo capacitor is one of them. Currently, the research of supercapacitors mainly focus on electrode materials. The electrode materials usually include carbon materials, transition metal oxides, conducting polymers, and even metal organic framework materials are also being improved to used as electrode materials. Porosity is the key factor that affect the performance of electrode materials, improve porosity of the electrode material is an effective way to obtain excellent capacitor performance. In this paper, we mainly research the preparation and pseudocapacitor performances of porous transition metal oxide and porous conducting polymer prepared by a unipolar polse electrodeposition method.Owing to the low price, high theoretical specific capacitance and simple preparation, the transition metal oxide of manganese dioxide(MnO2) has been widely studied. However, poor conductivity limit MnO2 to achieve the theoretical specific capacitance. In this work, manganese dioxide(MnO2) is deposited on multi-walled carbon nanotube(MWCNT) pre-covered onto Pt sheet by using a unipolar pulse electro-deposition(UPED) method and the composite electrode is prepared subsequently. Its contrast is also deposited using potentiostatic method(PM) to obtain composite electrode MnO2/MWCNT-PM. Observed by scanning electron microscopy(SEM), the composite electrode Mn O2/MWCNT-PM was formed by the accumulation of short nanorods, while the surface of the composite electrode MnO2/MWCNTUPED has a structure of nanometer arborization with loose and uniform porosity. The crystal form of both MnO2 have been studied by X-ray diffraction(XRD), found that both of them are amorphous. The FT-IR indicate that MnO2/MWCNT-UPED have more hydroxyl groups, suggest that the porous Mn O2 owing more hydrophilic groups and better compatibility to Na2SO4 solution. The electrochemical activity and specific capacitance of two MnO2 were investigated by cyclic voltammetry(CV). The electrode MnO2/MWCNT-UPED displays specific capacitance as high as 498.3 F·g-1, it can retain more than 97% of initial capacitance at the current density of 5 A·g-1 after 2000 cycles. While electrode MnO2/MWCNT-PM prepared with potentiostatical method shows only 334.4 F·g-1 and only retains 62% of its initial value at the same condition. The excellent performance of electrode MnO2/MWCNT-UPED is mainly contributed from the loose and stable structure of MnO2, which is deposited by using the UPED method.Because of facile synthesis, high stability, excellent electrochemical performance and low cost, polyaniline(PANI) has become one of the most widely studied conducting polymers. However, its available surface is limited. Preparation of polyaniline with high porosity and high conductivity by a simple method is very important. Metal-organic framework(MOF) materials with high surface area is selected as hard template for synthesizing porous PANI. Microporous PANI composite electrodes(Micro-PANI/CC) are fabricated by depositing aniline on to carbon cloth(CC) pre-coated with MOF material of HKUST-1 using a unipolar pulse electro-polymerization method. At the same time, PANI electrodes(PANI/CC) are also synthesized on carbon cloth for further comparatively. Their microstructure and morphology are characterized by XRD and SEM. Results indicate that electrode Micro-PANI/CC is composed of aggregated nanosized PANI spheres with nanopore structure. The cyclic voltammetry, constant current charge and discharge, impedance and stability tests are performed to evaluate the supercapacitor properties in 0.5 mol·L-1 sulfuric acid electrolyte. Specific capacitances of electrodes Micro-PANI/CC and PANI/CC are 895.6 F·g-1, 547.6 F·g-1 at scan rate of 2 mV·s-1, respectively. At the same given conditions, the specific capacitance of electrode Micro-PANI /CC is always 1.64 times than that of electrode PANI/CC. Meanwhile, electrode Micro-PANI/CC exhibits better rate capability, lower resistance and better stability of charge and discharge than PANI/CC. All the results imply that the microporous PANI templated from HKUST-1 is a good candidate for the electrode of supercapacitors.