| In recent years, electrochemical supercapacitors have received extensive attention with their attractive features including rapid charge/discharge capability, fast charge transfer, long cyclic life (> 106) and high power density (10 kW/kg) to fill the gaps left by batteries. Such advantages make them the most applicable in high power supply for both stationary and portable devices of digital communication, memory storage, electric cars and personal electronics.Supercapacitor mainly divided into electric double layer capacitor and Faraday capacitor (also called constraint capacitor), according to the different principle of the energy storage. The electrode materials are one of the key components determining the performance of supercapacitors and can be categorized mainly into three types:carbon-based materials, transition metal oxides, and conductive polymers. Carbon-based materials are the most widely studied serving as the electrode in electrochemical double-layer capacitors due to their excellent electrical conductivity, chemical stability, high specific surface area and low cost. However, at present most of the nannoproducts in market are prepared in the form of powder, which means they require to be mixed with conductive binders, and additives for the fabrication of electrodes. The process inevitably causes pollution of the electrode, which greatly limit the ion transfer between the electrode surface and the electrolyte and the movement of charge from the electrode surface to the current collector, hence, it is difficult to obtain supercapacitor with high energy storage. Several solutions have been proposed to solve these problems and explored in two major approaches:(1) hybirdization or doping on carbon in order to introduce Faradaic pseudo-capacitance; (2) preparing carbon film directly on the electric collector for fast charge transportation, that is, forming highly porous carbon film (PCF) which has been receiving enormous concern in lithium-ion batteries, supercapacitors and fuel cells. The PCF, especially serving in supercapacitors, demonstrates novel advantages including fast current response and high specific gravimetric capacitance.In the present work, highly PCF coated on nickel foam was prepared successfully by microwave plasma-assisted chemical vapor deposition (MPCVD) with C2H2 as carbon source and Ar as discharge gas for the electrode material in an electrochemical supercapacitor. The results show the PCF prepared under the flow rate of C2H2:Ar (15:1), the deposition time of 60 min and the microwave power of 1000 W has an excellent electrochemical performance. It displays the specific capacitance of 62.75 F/g in 30 wt.% KOH aqueous solution with the current density of 2.0 A/g, and 95% of the capacitance retains after 10,000 cycles at the current density of 2.0 A/g. Besides, Good near-rectangular shape of CV curves was obtained with various scan rates ranging from 50 mV/s to 1000 mV/s, which indicates good double-layer capacitance and high-rate capability.Then we designed the thermal treatment of the optimal sample. It found that the electrochemical performance of PCF treated under 500? has been obviously improved. At the current density of 3.0 A/g, the specific capacitance is 109.05 F/g and the energy density is 5.55 Wh/kg and the power density is 0.55 kW/kg, which is larger than PCF (3.40Wh/kg/0.52kW/kg) before thermal treatment. It highlights the potential of well-designed PCF for supercapacitance applications. |
PDF Full Text Request