Flexible Pseudo-capacitive Materials/Carbon Nanotube Film Electrode

In this paper, freestanding CNT films fabricated using CVD techniques are usedas flexible substrate. A combination of CNT film-based architechtures withpseudo-capacitive materials (MnO2and Ni(OH)2) has been designed as electrodes forsupercapacitors. We have conducted a series of structural and elecchochemicalcharacterization for these CNT film-based composite elctrodes.MnO2/CNT flexible electrodes have been synthesized by electrodeposition orsolution-based redox process. The as-prepared composite film exibits a specificcapacitance ranges from50~154F g-1, which is2~3times that of the prestine CNTfilms. Freestanding Ni(OH)2nanoflakes on CNT films (NNCF) electrode with highspecific capacitance is effectively fabricated via a facile chemical precipitationmethod. Take advantage of the slow and quite controllable reaction process, we havesuccessfully fabricated Ni(OH)2nanoflakes evenly coated on carbon nanotubeselectrode. The resulted ultrathin α-Ni(OH)2exhibits a high specific capacitance of3351F g-1at a scan rate of2mv s-1and a good cycling stability with a visibly lowcapacitance loss of15%at a high scan rate of70mv s-1. This ultrahigh specificcapacitance can be attributed to the following reasons. Firstely, the CNT networks inNNCF as the uniform nucleation sites for Ni(OH)2can effectively inhibit theaggregation of Ni(OH)2nanoflakes and provide more electrochemical active sites.Moreover, the uniform decoration of Ni(OH)2on CNT bundles, which in turn,prevents possible restacking of CNT bundles and improve the electrical double-layercapacitance of CNTs. In addition, as an excellent host material for the coating ofultrathin nanoflakes of Ni(OH)2, CNT films can provide a good electrical conductingpath for charge transfer and redox kinetics of the deposited layer. Based on the uniqueand desirable NNCF structure, we have further introduced parameter variables tomake a change to the mass loading and morphology of Ni(OH)2on CNT films.Ni(OH)2mass loading variation was achieved by changing the precursor reactantconcentration and the number of deposition time. Comparing the fabricated1/5NNCF(with precursor concentration half of the NNCF’s) and NNCF-2(with deposition time2times that of NNCF electrode) and the previous NNCF electrode, the utilization ofNi(OH)2reaches the highest in1/5NNCF electrode and a ultra-high specificcapacitance of3671F g-1together with a rather low capacitance loss of7%at high scan rates can be attained.By changing the types of precursor solvent, that is to replace potassiumpersulfate with ammonium persulfate, we intend to control its reaction speed tofurther affect morphology of the composite film. The results have shown that thereaction rate slows down a bit and the morphology of Ni(OH)2turned into granule.The granule Ni(OH)2shows a relatively lower capacitance compared to the nanoflakeNi(OH)2.