In situ generated bubble-mediated porous ionically conductive hydrogels for hydrogel-based electronics

Abstract

Ionically conductive hydrogels (ICHs) are increasingly explored in flexible electronic devices but the mechanoelectrical and electrochemical performances of hydrogel devices are often limited. Herein, bubble-mediated pores are established inside ICHs to achieve high sensitivity in pressure sensors and high-performance in rechargeable zinc-ion hybrid supercapacitors containing ICHs as electrolytes. CO₂ bubbles generated from an embedded reaction between weak acids and bases are trapped within the viscous polyvinyl alcohol/poly (sodium acrylic acid) (PVA/PAANa) pre-gel solution as a soft template. Cyclic freezing–thawing treatment of pre-gel solutions results in fully physically cross-linked ICHs containing pores that are regulated by acid–base reactions. Interestingly, by regulating the feed amount of acids and bases, porous channels are obtained in ICHs due to the orientation of rising bubbles in the precursor solution. Because of the synergistic capacitance effect from high-specific-area pores, the sensitivity of capacitive pressure sensors containing porous ICHs as electrodes is improved by 10 times. Additionally, porous ICHs also promisingly work as electrolytes in zinc-ion hybrid supercapacitors. Stable charge–discharge in nearly 30 000 cycles with high coulombic efficiency (∼100%) has been achieved. The bubble-mediated method is expected to provide a new pathway to improve the performance of hydrogel-based devices through structural regulation.