No abstract

Metal hexacyanoferrates (MHCFs), known as the Prussian blue analogues, with the general chemical formula AhMk[Fe(CN)6]r nH2O (where A = alkali metal cation, M = transition metal cation), are promising materials for electrocatalysts, charge-storage and sensor applications due to their unique structural characteristics such as three-dimensional (3D) network with a distinct tunnel and pore structures. It is well known that MHCF can exhibit solid state redox reactions associated with electrochemical insertion/extraction of various ions (Li+, Na+, K+, NH4 +, Mg2 +, etc.). For this reason, Prussian blue Analogues are currently being widely employed as active materials for alkali ion batteries and supercapacitive energy storage. In this work, the nickel(II)/cobalt(II) hexacyanoferrate(III) (Ni/Co-PBA)/graphene oxide composites were synthesized by co-precipitation method. XRD, FT-IR and Raman carried out their structural characterization, and morphological characterization was performed using SEM and TEM. The cyclic voltammetry results show two faradic processes associated to FeIII/ FeII and CoII/ CoIII redox couple which is accompanied by K+ ion insertion in and out of the cyanobridged metallic framework to maintain local charge neutrality. Adittionally, Electrochemical impedance spectroscopy was employed to study the impact of CoII/NiII ratio on the apparent diffusion coefficient for K+ in the material. The composites synthesized exhibited higher specific capacitance in acid medium within the potential range from 0 to 0.85 V vs Ag/AgCl (3M NaCl).