Facile synthesis of nanographene sheet hybrid α-MnO2 nanotube and nanoparticle as high performance electrode materials for supercapacitor

•Nanographene sheets are reversed directly from CO2 by a simple burn-quench method.•The obtained nano-carbon can react with KMnO4 solution to produce MnO2 composites.•The NGs hybrid MnO2 nanoparticles can be prepared at as low as temperature ∼40°.•The NGs hybrid MnO2 nanotubes can be synthesized at temperature ∼140°.•Enhanced electrical conductivity leads to electrochemical performance.

We have synthesized nanographene sheet (NGs) hybrid α-MnO2 nanotube (MTGs) and α-MnO2 nanoparticle (MPGs) by a joint method of burn-quench and hydrothermal. The NGs are prepared by directly reverting CO2 through a burn-quench method. The results indicate that these nano-carbons can easily react with KMnO4 to produce MPGs even at 40 °C and MTGs at 140 °C, respectively. The electrochemical measurements show the MTGs and MPGs have excellent electrochemical properties as supercapacitor electrode materials. The specific capacitance values for the MPGs and MTGs can get up to about 171.3 and 290.6 F g−1 at current density of 1 A g−1 in 1 M Na2SO4 electrolyte, respectively. Moreover, after 3000 cycles at a rate of 1 A g−1, the corresponding specific capacitances are 150.6 F g−1 for MPGs and 265.4 F g−1 for MTGs materials, which reveals the good retention of capacity upon cycling.