Potential Co2+ and Ni2+ intercalation into nickel hexacyanoferrate in aqueous media: Study of electrochemical process and multivalent batteries implications

Alternative energy storage systems to lithium-ion batteries that can reduce the dependency on such technology have attracted great interest in recent years. Besides their current limitations, multivalent batteries based on coupling a metallic anode (Mg, Zn, Ca…) with a multivalent intercalation cathode are considered as a potential option. Prussian Blue Analogues (PBAs) have shown promising multivalent intercalation capacities and have also been employed in other scientific fields like wastewater treatment, selective element extraction, and may have a potential applicability in batteries recycling. However, some controversies have recently appeared around the capacity of PBAs to incorporate multivalent cations in aqueous media. In this work, we analyze by a combinatorial approach using structural and electrochemical techniques the potential Ni2+ and Co2+ intercalation in K0.61Ni[Fe(CN)6]0.84□0.16·2.12H2O, its limitations, the role of proton intercalation and the cation released after oxidation, which differed from the intercalated during previous reduction step. The potential implications of such findings in current uses of PBAs for multivalent batteries are also discussed.