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Hydrogel electrolytes have high room-temperature conductivity and can be widely used in energy storage device. However, hydrogels suffer from the inevitable freezing of water at subzero temperatures, resulting in the diminishment of their conductivity and mechanical properties. How to achieve high conductivity without sacrificing hydrogels' flexibility at subzero temperature is an important challenge. To address this challenge, a new type of zwitterionic polymer hydrogel (polySH) electrolytes is fabricated. The anionic and cationic counterions on the polymer chains facilitate the dissociation of LiCl. The antifreezing electrolyte can be stretched to a strain of 325% and compressed to 75% at −40 °C and possesses an outstanding conductivity of 12.6 mS cm −1 at −40 °C. A direct hopping migration mechanism of hydrated lithium-ion through the channel of zwitterion groups is proposed. The polySH electrolyte-based-supercapacitor (SC) exhibits a high specific capacitance of 178 mF cm −2 at 60 °C and 134 mF cm −2 at −30 °C with a retention of 81% and 71% of the initial capacitance after 10 000 cycles, respectively. The overall merits of the electrolyte will open up a new avenue for advanced ionic conductors and energy storage device in practical applications.

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Density fingering of exothermic autocatalytic fronts in vertically oriented porous media and Hele-Shaw cells is studied theoretically for chemical reactions where the solutal and thermal contribution to density changes have opposite signs. The competition between these two effects leads to thermal plumes for ascending fronts. The descending fronts behave strikingly differently as they can feature, for some values of the parameters, fingers of constant amplitude and wavelength. The differences between up and down going fronts are discussed in terms of dispersion curves and nonlinear dynamics. The theoretically predicted dispersion curves are experimentally evidenced with the chlorite-tetrathionate reaction.

We consider the density fingering of exothermic autocatalytic fronts in vertically oriented Hele-Shaw cells with chemical reactions whose solutal and thermal contributions to density changes have opposite signs. Using the Darcy-Boussinesq equations we examine the influence of the competition between solutal and thermal density changes on the linear stability of traveling fronts and the fully nonlinear dynamics. Ascending fronts are characterized by standard Rayleigh-Taylor fingering dispersion curves and in the nonlinear stage of the instability they feature thermal plumes. Descending fronts on the other hand behave strikingly differently as they can feature for some values of the parameters Turing-type dispersion curves and stationary patterns with fingers of constant amplitude and wavelength.

We consider the buoyancy driven Rayleigh-Taylor instability of reaction-diffusion acidity fronts in a vertical Hele-Shaw cell using the chlorite-tetrathionate ͑CT͒ reaction as a model system. The acid autocatalysis of the CT reaction coupled to molecular diffusion yields isothermal planar reaction-diffusion fronts separating the two miscible reactants and products solutions. The reaction is triggered at the top of the Hele-Shaw cell and the resulting front propagates downwards, invading the fresh reactants, leaving the product of the reaction behind it. The density of the product solution is higher than that of the reactant solution, and hence a hydrodynamic instability develops due to unfavorable density stratification. We examine the linear stability of the isothermal traveling wavefront with respect to disturbances in the spanwise direction and demonstrate the existence of a preferred wavelength for the developed fingering instability. Our linear stability analysis is in excellent agreement with two-dimensional numerical simulations of the fully nonlinear system.

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