Colloidal WO2.72 Nanocrystals with Hexagonal Tunnels for Sodium-ion Supercapacitors

초록

Although sodium-ion supercapacitors are promising candidates for next-generation electrochemical systems, their performance is often hindered by the relatively large ionic radius of Na⁺, which limits facile ion insertion and thus suppresses capacity enhancement. The high surface area and large hexagonal tunnels make colloidal monoclinic WO2.72 nanocrystals attractive as electrode materials, but their use in Na⁺-based supercapacitors remains unexplored. In this study, we introduce colloidally synthesized monoclinic WO2.72 nanocrystals capable of effectively accommodating Na⁺ ions within their hexagonal sites for Na+-based supercapacitors. By removing insulating organic ligands, the nanocrystals are uniformly deposited onto hydrophilic carbon cloth (CC) through a controllable, additive-free dip-coating process. Furthermore, applying a conformal 1 nm Al2O3 overlayer via atomic layer deposition (ALD) enhances mechanical robustness and prevents nanocrystal delamination, enabling highly reversible charge-storage behavior. A symmetric supercapacitor fabricated with ALD-treated WO2.72/CC and a PVA/Na2SO4 gel electrolyte demonstrates stable performance without degradation under bending, achieving an areal energy density of 10.08 µWh/cm2 at 0.3724 mW/cm2. These results highlight the potential of colloidal nanocrystal-based electrodes for high-performance sodium-ion supercapacitors suitable for practical, wearable electronic applications.

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