Hydrogel electrolytes regulated by hydroxypropyl methylcellulose and hydroxyethyl cellulose for zinc-ion hybrid supercapacitors.

The practical application of zinc-ion hybrid supercapacitors (ZIHSCs) is limited by the trade-off between interfacial stability and ion transport in aqueous electrolytes. Herein, two cellulose ethers with distinct substituent structures, hydroxypropyl methylcellulose (HPMC) and hydroxyethyl cellulose (HEC), were introduced as regulatory components to construct composite hydrogel electrolytes, denoted PASMCE and PASECE, respectively. Their effects on water states, network morphology, ion transport, and electrochemical behavior were comparatively investigated. HPMC, containing relatively hydrophobic methoxy and amphiphilic hydroxypropyl substituents, promoted a denser network and stronger water confinement. These features were associated with a wider electrochemical stability window of 2.33 V, lower hydrogen-evolution and corrosion currents, and improved Zn interfacial stability. In contrast, HEC promoted a more open freeze-dried network morphology and higher ionic conductivity, enabling PASECE-based ZIHSCs to deliver a specific capacity of 105.3 mAh g-1 at 0.75 A g-1 and a maximum energy density of 115 Wh kg-1 at 825 W kg-1. These findings demonstrate that cellulose ethers can serve as regulatory polymeric components for tailoring hydrogel electrolyte microenvironments and balancing ion transport with Zn interfacial stability.