Synthesis and control of high-performance MnO2/carbon nanotubes nanocomposites for supercapacitors

Abstract

The rational combination of transition-metal oxides and carbon materials has been regarded as an efficient way of assembling the next-generation of electrode materials for supercapacitors. Here, a unique nanomaterial consisting of carbon nanotubes (CNTs) grafted with MnO2was synthesized for use in supercapacitors with high electrochemical performance. The synthesis was performed in three steps: surface functionalization of the CNTs with carboxyl groups, grafting of Mn2+with the carboxyl groups, and transformation of the Mn2+into MnO2nanoparticles by KMnO4oxidation. The bonds between the CNTs and the MnO2particles are believed to form between the carbon of the carboxyl groups of the CNTs and the oxygen atoms of the MnO2lattice. In addition, varying the acid-treatment time enabled control of the growth density of MnO2and affected the structural integrity of the CNTs, endowing the novel hybrid material with an adjustable electrochemical performance. As a consequence, the MnO2/CNTs composite with a 36 h acid treatment exhibited a maximum specific capacitance of up to 348 F g−1at a cyclic voltammetry scanning rate of 5 mV s−1. A symmetric supercapacitor assembled with the electrodes made from this MnO2/CNTs composite showed a capacitance decay rate of only 8.7% after 5000 cycles.