Bricks of Co, Ni doped Fe3O4 as high performing pseudocapacitor electrode

Iron oxide has been a widely used electrode material for energy storage devices. It has also been recently utilized in magnetic supercapacitors. To improve its performance, a strategy of co-doping with cobalt and nickel is proposed. This leads to nearly 85 % improvement in the performance, which can be further tuned by varying the concentrations of cobalt and nickel. Performance of Ni1-xCoxFe2O4 (x = 0, 0.3, 0.5, 0.7 and 1.0) is discussed in the paper. Owing to the varying order of electrolyte ions in different materials, the specific capacitance value also changes. This is established using a theoretical model. Performance of an asymmetric device, fabricated using optimized composition i.e. Ni0.5Co0.5Fe2O4 as positive and graphene oxide (GO) as the negative electrode is also presented. The asymmetric Ni0.5Co0.5Fe2O4//GO device is able to deliver high energy density i.e. 21.5 Wh kg-1 and excellent cyclic stability (-92 % after 5000 cycles).