Process development for Roll-to-Roll Carbon Nano Tube (CNT) Growth.
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This study presents the process development for the synthesis of dense multiwalled carbon nanotube (CNT)- based high energy density electrodes for supercapacitors at pilot scale using an industrial roll-to-roll chemical vapour deposition facility. Pre-etched aluminium foil was used as substrate, where the catalyst nanoparticles of nickel were deposited through sputtering and NiSO₄ solution coating methods. The morphology and distribution of Ni nanoparticles and the growth mechanism of carbon nanotubes were studied thoroughly. Atmospheric pressure chemical vapour deposition (AP-CVD) was performed at 580 oC with synthesis time varying from 15 minutes to 180 minutes. This study majorly focused on the study of pilot production facility as it is not only more than 100 times larger in volume than the lab scale CVD reactor, but also possesses several additional challenges that makes it complicated to replicate the synthesis process from lab scale to industrial scale. Hence a systematic investigation of optimal gas ratios, flowrates, concentration, oxide reduction for solution coated samples, heating rate of the sample and segregation of gases was necessary due to the high sensitivity of the CNT growth mechanism to different conditions. Under optimal gas concentration and synthesis time it was possible to achieve high energy dense CNT electrodes with a record- high gravimetric capacitance of 78 F/g and areal capacitance of 1253 mF/cm², whereas the best/state-of-the-art industrial values are 60 F/g and 700 mF/cm², respectively, using activated carbon (AC) based electrodes.