Investigation on the Keggin Anchored on Hydroxide-Functionalized Single-Walled Carbon Nanotubes as Superior Cathode for Aqueous Zinc-Ion Batteries

Rechargeable aqueous zinc-ion batteries (AZIBs) have become a viable option in electrochemical energy storage systems (EESS) owing to their inherent safety features and economic friendliness. Nonetheless, creating suitable cathode materials for AZIBs with high structural stability, good rate performance, and great capacity remains a significant challenge. Polyoxometalate (POM)-based nanohybrid materials have shown promising results in high cycling stability and great specific capacity. However, POMs susceptible to electrolyte dissolution and the sluggish Zn-ion (Zn²⁺) kinetics have significantly hampered their electrochemical performance as cathodes for AZIBs. Herein, we present a Keggin POM, K₃[PW₁₂O₄₀]·nH₂O (KPW₁₂), anchored on hydroxyl (OH)-functionalized single-walled carbon nanotubes (SWOH) that were fabricated via a facile ultrasonication procedure. Employed as cathodes for AZIBs, the optimal KPW₁₂/SWOH feature exhibited remarkable electrochemical performance. The system satisfied the Zn²⁺ storage, achieving a reversible discharge capacity of 183 mAh g^–1 at a high current density of 5C with a flat and long discharge plateau after 160 cycles. The perfect synergistic contribution of the pseudocapacitive nature of the super-reduced state of KPW₁₂ and the electron-conductive network of SWOH was attributed to this exceptional electrochemical performance. Furthermore, the presence of oxygen in SWOH enhanced the transfer kinetics of electrons and smooth Zn²⁺ diffusion while lowering the Zn²⁺ migration energy barrier by providing more accessible active sites. This demonstrates remarkable promise in fabricating robust electrode materials optimized for integration within aqueous battery systems that pave the way for further research into POM-based materials for EESS.