Rarely negative-thermovoltage cellulose ionogel with simultaneously boosted mechanical strength and ionic conductivity via ion-molecular engineering

Abstract

Excellent mechanical strength and conductivity are essential and exigent features for advanced gel materials. The trade-off between them, however, remains a challenge. Here, we proposed an ion-molecular engineering strategy to develop a strong (4.46 MPa) yet high conductivity (67.43 mS cm⁻¹), freezing tolerant (−103 °C), and transparent (94%) cellulose ionogel via ZnCl₂ doping (namely CZ ionogel). Doping Zn²⁺ induces coordination interactions with cellulose molecules (Zn²⁺–COO⁻) through coupling hydrogen bonding and ion–dipole interactions, resulting in a robust CZ ionogel with 15- and 10-times improvement in the elastic modulus and toughness, respectively. The Zn²⁺–cellulose engineering produces a confined nanostructure that supports the efficient transport of small-size Cl⁻ anions, while limiting the movement of large-size cations, thereby allowing the CZ ionogel to function as a rare n-type ionic thermoelectric material to convert low-grade waste heat into useful electricity (∼110 mV at ΔT = 36 K). This ion-molecular engineering strategy offers unprecedented degrees of freedom for developing adaptable gel materials.