Direct Growth of Carbon Nanofibers on Nickel Foam and Its Application As Electrochemical Supercapacitor Electrodes

Carbon nanofibers (CNF) are useful for many applications such as polymer reinforcement, electrochemical devices like sensors, batteries, and supercapacitors. The most common method of producing them is by catalytic chemical vapor deposition (CVD) or by electrospinning. CNF growth using CVD is a single step process, unlike electro spinning which requires an additional carbonization step at higher temperatures. In CVD the catalyst is either incorporated directly onto the substrate or introduced with the feed gases. This adds extra cost and set limits to the design of the systems used for the CNF growth process, particularly in cases where porous structures are envisioned. In supercapacitors, the electrode material is most often painted or deposited with an ink of carbon particles. Directly growing the carbon nanomaterial from the supporting surface would eliminate this step and allow complex geometries. It would also help in achieving a higher capacitance by removing the requirement of a binder material and eliminate the occurrence of agglomeration of the active material inherent in the ink deposition process. Another advantage is the higher conductivity of CNF compared to the commonly used active carbon material. With CNF growing directly of the current collector, the addition of conductive carbon black can possibly be eliminated. Finally, an increase access of the electrolyte to the electrode can be expected due to the natural 3-D nano-architecture formed by the CNF. On the other hand, the micro-scale 3-D structure of nickel foams have been the most sought after substrates (current collectors) in the battery and supercapacitor research as they offer more surface area for the deposition of the required active material, together with being non-corrosive in alkali medium. CNF grown directly on Ni-foams are thus expected to extend the performances of supercapacitor electrodes. In this work, we have found a novel method of growing dense CNF on nickel foam. Cyclic voltammetry, galvanotactic charge discharge, and electrochemical impedance spectroscopy was made to electrochemically characterize these CNF/Ni-foam supercapacitor electrodes. When tested as a supercapacitor electrode in 6M KOH, our directly grown CNF gives a good aerial capacitance of about 60 mF/cm2 and an energy density of 16 mWh/m2. We believe this nickel foam with CNF to be very useful in supercapacitors and batteries in decreasing the resistance of the electrochemical device and provide additional surface area.

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