Preparation Of Aligned Carbon Nanotube Array Electrode And Its Application To Supercapacitors

Supercapacitors is a new type of power energy-storage device.Comparing with rechargeable batteries,supercapacitors feature high specific power,broad operating temperature range and long cycle life.The promising application areas of supercapacitors include mobile telecommunication,information technology, consumer electronics,electric vehicles,military and aviation & aerospace.Majority of the commercial supercapacitors today use activated carbon electrodes,however, the performance of such supercapacitros is limited by the poor activated carbon conductivity and surface irregularity,non-uniform pore size and carbon impurity. Carbon Nanotubes(CNTs)is a better electrode material theoretically for supercapacitors due to its high conductivity and unique structure.Many research groups reported that supercapacitors based CNTs electrode showed excellent electrochemical properties.Aligned Carbon Nanotube Arrays(ACNTAs)could be an appropriate electrode material for supercapacitors application because of the unique arrangement of CNTs.In this dissertation,research work has been carried out to investigate the influence of preparation conditions on properties of ACNTAs,and the parameters for optimized conditions were obtained.Also ACNTAs were successfully grown on metal substrates.Such obtained ACNTAs were used directly as electrode materials for supercapacitors and electrochemical properties were investigated. Through a series of experiments,the following conclusions were drawn;1.ACNTAs with 210μm in length were prepared by pyrolysis of iron(â…¡) phthalocyanine(FePc)and C₂H₄ on quartz substrate.The as-grown ACNTAs were well-aligned,pure and highly crystallized.We systemically investigated the influence of experimental parameters,such as temperature,growth time,and flow rate of gas (H₂ and C₂H₄),on the formation of ACNTAs.The results indicated that 800℃was the most suitable temperature for preparation of long ACNTAs by pyrolysis of FePc and C₂H₄,the activity of catalyst could be kept for a rather long time(60 min),the addition of C₂H₄ significantly enhanced the growth speed of ACNTAs and 50 cm³ min^-1was found to be the optimal flow rate for the formation of ACNTAs.The optimal flow rate of H₂ was 40 cm³ min^-1.2.A tree-branch-like structure ACNTAs was obtained by pyrolysis of FePc under Ar ambient.The growth process of this special structure was studied and the possible reason of its formation was also given.3.Some disorderly entangled CNTs were obtained by pyrolysis of FePc and C₂H₄ directly on metal alloy substrate(Inconel 600).ACNTAs with several micrometers in length were synthesized while Inconel 600 was emerged in dense strong acid(H₂SO₄ or HNO₃),however,the as-grown sample was not uniform on the substrate.ACNTAs with a length of 150μm were grown when the Inconel 600 was deposited with a 20 nm Al₂O₃ film in advance.When the Inconel 600 with 20 nm Al₂O₃ film was emerged in a surfactant(NaAOT)and thioacetamide subsequently, ACNTAs with 280μm in length could be obtained.4.The as-obtained ACNTAs grown on Inconel 600 were used directly as electrode materials in supercapcitors with 1.0M(Et)₄NBF₄ + Propylene Carbonate (PC)as electrolyte and then e(?)trocbemical properties were investigated.A rectangular-shaped Cyclic Voltammetric(CV)curve was observed even at a sweep rate of 1000 mV s^-1.The specific capacitance measured at 1000 mV s^-1was about 57 %(47 F g^-1)of that obtained at 1 mV s^-1(83 Fg^-1).After 1000 cycles,only a slight decrease of C_spcan be observed.This result indicates an excellent stability of the ACNTA electrode,and an Equivalent Series Resistance(ESR)of 0.55 ohm was measured,which demonstrate the good contact between the ACNTAs and the substrate and the electrolyte can quickly diffuse into the forest of ACNTA electrode. The results obtained by galvanostatic charge-discharge test were well in agreement with the CV results.The specific energy was 28.8 Wh kg^-1and the average specific power could reach 1200 W kg^-1under 1mA constant current.These results indicated that the ACNTAs could be a promising candidate as electrode materials in supercapacitors.