Tailoring the capacitive performance of ZnCo₂O₄by doping of Ni²⁺and fabrication of asymmetric supercapacitor

Doping with d-block metal ions plays a pivotal role in enhancing the specific capacity (Cg) of metal oxides. Here, augmenting the electrochemical performance of ZnCo2O4 is demonstrated by Ni2+ ion doping. An enormous boost in Cg after doping with Ni2+ was noticed due to the high electrical conductivity of Ni. In addition, doping with Ni leads to excellent rate capability and long cycle life. An asymmetric supercapacitor (ASC) fabricated using Ni2+ doped ZnCo2O4 and reduced graphene oxide (rGO) in 3.5 M KOH electrolyte displays an excellent energy density of 40 W h kg-1 and power density of 775 W kg-1 at 1 A g-1. In addition, an all-solid-state flexible asymmetric supercapacitor (ASFAS) device was fabricated to demonstrate its application in flexible electronics. Surprisingly, the as-prepared ASFAS device achieved a high energy density of 26 W h kg-1. Moreover, the device retained 95% of its original capacity over 10 000 cycles.