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 Co 3 O 4 and NiO. Benefited from the enhanced micromixing performance and higher supersaturation level, the highly developed MISR (Reynold number ( Re j ) > 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 Re j . The electrochemical measurements demonstrated that Ni-Co-O composites prepared in MISR at Re j  = 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.