Formation of ultra-small Mn3O4 nanoparticles trapped in nanochannels of hollow carbon spheres by nanoconfinement with excellent supercapacitor performance

Ultra-small Mn3O4 nanoparticles are formed in the shell of hollow carbon spheres (HCS-Mn3O4) via nanoconfinement growth. The HCS with special cylindrical channels (about 2 nm) provides the limited space for growth of Mn3O4 nanoparticles and serves as a conductive substrate in electrochemical applications. The unique hollow structure shortens the distance for electrolytes to access Mn3O4 during the charging/discharging process. In the hybrid HCS-Mn3O4 structure, the interaction between Mn3O4 nanoparticles and HCS was enhanced resulting in good conductivity and electrochemical properties. The two-electrode supercapacitor cell composed of HCS-Mn3O4 shows high capacitance and energy density. The highest specific capacitance of 430 F g(-1) is achieved at a scanning rate of 1 mV s(-1) and the largest energy density of 13.5 Wh kg(-1) is observed at a power density of 0.3 kW kg(-1) by HCS-Mn3O4-5 with 93.15% retention after 10,000 cycles in 5 M LiCl. Symmetric HCS-Mn3O4-5//HCS-Mn3O4-5 shows higher energy density of 22.6 Wh kg(-1) at a power density of 0.4 kW kg(-1) and power density of 3.3 kW kg(-1) at an energy density of 16 Wh kg(-1) with 1 M Li2SO4. The technique to prepare the HCS-Mn3O4 hybrid materials is simple and readily scalable to satisfy industrial demand. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.