Copper hexacyanoferrate with a well-defined open framework as a positive electrode for aqueous zinc ion batteries

The feasibility of the electrochemical zinc ion insertion/extraction reaction in CuHCF nano-cube in aqueous solution is investigated. It is demonstrated for the first time that the divalent zinc ions can be reversibly inserted/extracted into/from CuHCF nano-cube in aqueous solution due to the small radius steric effect of zinc ions. The zinc ion insertion and extraction is controlled by the solid phase diffusion into/from the CuHCF electrode. Divalent cation (de)intercalation discovered in this work expands perspectives on intercalation electrochemistry of divalent cations, and it will possibly lead to development of novel divalent cation intercalation compounds for aqueous rechargeable batteries.