Optimizing NH4+ Storage Capability of Nickel Ferrocyanide by Regulating Coordination Anion in Aqueous Electrolytes

Abstract Will anions in electrolytes affect the electrochemical properties of Prussian blue analogues for aqueous ammonium ion batteries? In this study, the electrochemical reaction between nickel ferrocyanide and ammonium ions is investigated in three common inorganic ammonium salt solutions [NH 4 NO 3 , NH 4 Cl, and (NH 4 ) 2 SO 4 ]. The results suggest that at the same NH 4 + concentration, nickel ferrocyanide exhibits different electrochemical performances. The as‐prepared nickel ferrocyanide contains two phases, which are rhombohedral phase and cubic phase. Rhombohedral phase of nickel ferrocyanide has a high reactivity in 0.5 M (NH 4 ) 2 SO 4 solution during cycling while cubic phase shows good performance in 1 M NH 4 NO 3 and 1 M NH 4 Cl electrolyte. It should be noted that the performance of cubic phase is superior to rhombohedral phase in kinetic consideration. Additionally, due to the strong coordination ability of chloride, nickel ferrocyanide exhibits an excellent electrochemical performance in 1 M NH 4 NO 3 solution, rather than 1 M NH 4 Cl electrolyte.