Enhanced Electrochemical Performance of Bimetallic Doped Ni-Based Metal–Organic Frameworks by Redox Additives in an Alkaline Electrolyte

A Cu2+ and Zn2+ bimetallic doped metal–organic framework Ni2(bdc)2(dabco) (CuZnNi–MOF, where bdc is 1,4-benzenedicarboxylic acid and dabco is 1,4-diazabicyclo[2.2.2]-octane), has been successfully synthesized by the solvothermal method. The carbon-held metal compound nanoparticles (MCN@C) and metal oxide composite (CuOZnONiO) were subsequently obtained by using the CuZnNi–MOF as the precursor. The electrochemical performance of the prepared samples was evaluated in an electrolyte with and without a redox additive (K4Fe(CN)6). The specific capacity of the samples tested in the electrolyte with Fe(CN)64–/Fe(CN)63– has a high value of 112.5 mA h g–1 at 1 A g–1, which is much higher than that measured in the electrolyte without the redox additive, indicating that the Fe(CN)64–/Fe(CN)63– redox couple can effectively enhance the electrochemical performance of electrode materials. An asymmetric supercapacitor (ASC) CuZnNi–MOF//PEDOT-AC (poly(3,4-ethylenedioxythiophene)-activated carbon) was further assembled and tested in 3 M KOH + 0.05 MK4Fe(CN)6 electrolyte. The ASC shows a high energy density of 25.2 W h kg–1, a maximum power density of 8 808 W kg–1, and also superb cycling performance. Moreover, two assembled ASCs in series connection are found to be able to light up a red light-emitting diode for at least 20 min.