Synthesis, Characterization, and Electrochemical Behavior of Ternary Ni–Co–Fe Prussian Blue Analogues

We present a systematic investigation on the structural and physical features of a series of ternary Prussian blue analogues (t-PBAs) based on cobalt, nickel, and iron (Co/Ni ratio varied from 0 to 1), coupled with the study of their electrochemical performance as potential supercapacitors. The materials are prepared through the well-established coprecipitation method in water, proving it as a robust approach for a fine <i>on demand</i> modulation of their composition. The increase of the Co content rules the extent of crystallite sizes, as well as the strength of the bond in the iron-cyanide ligand, through internal charge exchange between these two transition metal ions. The relative amount of Co and Ni, on the other hand, significantly affects their electrochemical behavior: the formal potentials, the current generated under voltage scanning, the resistance to long bias solicitations, and the characteristics of galvanostatic charge-discharge are all affected by this parameter. A mixed charge storage control mechanism is observed for both capacitive and diffusive processes for the entire batch. The supercapacitive behavior is investigated as well, showing no obvious dependence on material composition, although fairly good performance in terms of capacitance and capacitance retention is recorded.