Microreactor facilitated preparation and Ni-doping of MnO2 nanoparticles for supercapacitors

Clustered countercurrent-flow micro-channel reactors (C-CFMCR) with varying magnification times were applied for the preparation of Ni-doped manganese dioxide (Ni-MnO2) via co-precipitation processes. Effects of the feeding flow rate of reactants and the concentration of the doping agent on the doping processes were investigated. The C-CFMCR, which is of intensified micromixing efficiency as compared with conventional stirred reactors (STR), played a crucial role in facilitating the uniform nucleation and growth of MnO2 crystals and then the doping of Ni. As a result, the prepared Ni-MnO2 had a decreased particle size and a more uniform microporous structure. EDS analysis showed an even distribution of Ni2+ within the nanocomposites and thus enhanced electrochemical performance of the MnO2 composite materials as supercapacitor electrodes was achieved. The 1.0 at% Ni-MnO2 nanocomposites prepared under optimal conditions exhibited the highest specific capacitance of similar to 389.6 F g(-1) at a current density of 1 A g(-1) and showed excellent cycling stability with 79.3% retention of the initial capacitance after 5000 charge/discharge cycles in 2 M KOH aqueous solution. The as-assembled Ni-MnO2//activated carbon (AC) asymmetric supercapacitor displayed a wide operating voltage (0-1.6 V), high energy and power densities (13.3 W h kg(-1) and 187.52 W kg(-1) at 0.25 A g(-1), respectively), and a stable cycling behavior (83.8% capacitance retention after 1000 cycles at 1 A g(-1)). In addition, only a weak scaling-up effect of C-CFMCR on the co-precipitation process was observed, suggesting that C-CFMCR is a prospective technique for the continuous and large-scale production of nanoparticles. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study focused on preparing Ni-MnO2 using C-CFMCR reactors with different magnification times, investigating the effects of reactant flow rate and doping agent concentration. The highly efficient micro-mixing capability of the C-CFMCR facilitated uniform nucleation and growth of MnO2 crystals and Ni doping, resulting in smaller particle size and more uniform microporous structure of Ni-MnO2. This enhanced electrochemical properties, leading to high specific capacitance and cycling stability in supercapacitor electrodes, showing potential for large-scale nanoparticle production.