Application of micro-impinging stream reactors in the preparation of Co and Al co-doped Ni(OH)2 nanocomposites for supercapacitors and their modification with reduced graphene oxide.

A micro-impinging stream reactor (MISR) consisting of a commercial T-junction and steel capillaries, which is of intensified micromixing efficiency as compared with traditional stirred reactors (STR), was applied for the preparation of Co and Al co-doped Ni(OH)2 nanocomposites and their modification with reduced graphene oxide (RGO). The co-precipitation preparation process was conducted under precisely controlled proportions and concentrations of reactants in the MISR. Therefore, element analysis showed a higher uniform distribution of metal ions within the nanocomposites obtained through the MISR. The structural characterization and electrochemical measurements also showed that the MISR-prepared metal-doped nanocomposites were of more uniform dispersion and superior electrochemical performance than those prepared with STR. In addition, by modifying with RGO in the MISR, the electrochemical performance of Co and Al co-doped Ni(OH)2 nanocomposites could be further improved. The Co and Al co-doped Ni(OH)2/RGO prepared under optimal conditions achieved an ultrahigh specific capacitance of 2389.5 F g-1 at the current density of 1 A g-1 and displayed an excellent cycling stability with 83.7% retention of the initial capacitance after 1000 charge/discharge cycles in 6 M KOH aqueous solution.