Comparing Graphene and Carbon Nanotubes as Nanoscale Current Collectors in MnO₂-Based Supercapacitors

Recently, both graphene and carbon nanotubes were shown to improve the overall performance of supercapacitors by acting as nanoscale current collector. Even though both of them are made from pure carbon, their structures are very different. How would the differences in their structures affect their roles in a supercapacitor system is a very interesting question. Here, we evaluated both materials in MnO₂ based supercapacitor systems in order to answer this question. The composites of RGO/MnO₂ were synthesized through a simple but effective chemical co-precipitation method and have specific surface area ∼220 m²/g. Electrochemical measurements show that the efficiency of MnO₂ was greatly improved, with the specific capacitance generally higher than 300 F/g (at 10 mV/s) and 55%∼65% of the high C_sp retained at 500 mV/s across a range of material ratios and mass loading densities. Compared with RGO, FWNTs was able to provide MnO₂ better performance as ultra-thin film due to its higher conductivity. However, as the film goes thicker, the electrolyte ion diffusion resistivity across the composite film seems to become the major limitation and these two composites behave very similarly.