Cobalt Ion-Stabilized VO₂ for Aqueous Ammonium Ion Hybrid Supercapacitors

Aqueous ammonium ion hybrid supercapacitor (A-HSC) is an efficient energy storage device based on nonmetallic ion carriers (NH 4 + ), which combines advantages such as low cost, safety, and sustainability. However, unstable electrode structures are prone to structural collapse in aqueous electrolytes, leading to fast capacitance decay, especially in host materials represented by vanadium-based oxidation. Here, the Co 2+ preintercalation strategy is used to stabilize the VO 2 tunnel structure and improve the electrochemical stability of the fast NH 4 + storage process. In addition, the understanding of the NH 4 + storage mechanism has been deepened through ex situ structural characterization and electrochemical analysis. The results indicate that Co 2+ preintercalation effectively enhances the conductivity and structural stability of VO 2, and inhibits the dissolution of V in aqueous electrolytes. In addition, the charge storage mechanisms of NH 4 + intercalation/deintercalation and the reversible formation/fracture of hydrogen bonds were revealed.