Fast coprecipitation of nickel-cobalt oxide in a micro-impinging stream reactor for the construction of high-performance asymmetric supercapacitors

Abstract

Precipitation is a convenient process for the massive production of materials in industry due to its fast kinetics and mild reaction conditions. In this work, a micro-impinging stream reactor (MISR) was constructed as a process intensification equipment to synthesize transition metal oxides via ambient-temperature precipitation. The as-prepared Ni-Co-O composites showed a loose mesoporous structure consisting of aggregated spherical nanoparticles with a mean size of ∼50 nm, which exhibited much smaller particle size, larger BET surface area and superior electrochemical performance as compared to Co3O4 and NiO. Benefited from the enhanced micromixing performance and higher supersaturation level, the highly developed MISR (Reynold number (Rej) > 3000) could produce smaller and more uniform Ni-Co-O aggregates with larger BET surface area as well as higher specific capacitance than those prepared in traditional stirred tank reactor (STR) and in MISR at low Rej. The electrochemical measurements demonstrated that Ni-Co-O composites prepared in MISR at Rej = 3160 displayed a high specific capacitance of 2012 F g−1 at the current density of 1 A g−1 as well as good rate capability and cycle stability. Furthermore, a Ni-Co-O//AC asymmetric supercapacitor assembled with the Ni-Co-O composites and activated carbon exhibited remarkable performance with a high energy density of 48.3 W h kg−1, a maximum power density of 7.6 kW kg−1, and excellent capacitance retention of 90.2% after 3000 cycles. The results illustrated that MISR is a promising and powerful process intensification technology for the fast production of Ni-Co-O composites that can be used as high performance supercapacitor electrode materials.