Scalable thermal synthesis of a highly crumpled, highly exfoliated and N-doped graphene/Mn-oxide nanoparticle hybrid for high-performance supercapacitors

Abstract

A scalable thermal method to synthesize a highly crumpled, highly exfoliated and N-doped graphene/Mn-oxide nanoparticle hybrid for high performance supercapacitors has been demonstrated. Reduction of graphene-oxide (GO), nanometer scale crumpling, high level of exfoliation, N-doping of graphene and decoration with Mn-oxide nanoparticles, each of which significantly contributes to a high specific capacitance (958 F g⁻¹ at 5 mV s⁻¹) in a synergetic way, are achieved in a single thermal process, thermal annealing of GO–Gly–Mn(NO₃)₂·4H₂O mixture at 500 °C followed by a rapid quenching with liquid nitrogen. N-doping of graphene is predominantly done in the form of pyrrolic-like and pyridine-like nitrogens, and Mn-oxide nanoparticles are formed on the surface of graphene as MnO₂ and Mn₃O₄. The nanometer scale crumpling of graphene sheets, which is achieved by rapid quenching of graphene in the presence of Mn-oxide nanoparticles on its surface, induces an exceptionally high degree of exfoliation of graphenes and prevents restacking of graphene sheets during a repeated charge–discharge process, providing a high specific surface area (1006 m² g⁻¹) and high cycle stability (94.1% retention after 1000 cycles), respectively. The simplicity of the synthesis process and the high performance of supercapacitors make it an easily scalable and industrially applicable method.