Non-Drying Hydrogel Polyelectrolytes via Polymer-Assisted Cation Solvation-Confinement Toward H₂O for Ultrahigh-Voltage Aqueous Micro-Supercapacitors.

Abstract

Conventional hydrogel electrolytes often encounter challenges such as poor water retention and a limited electrochemical window due to inadequate control over water molecules, leading to a low operational voltage and an undesirable low energy density of pure aqueous micro-supercapacitors (MSCs). Herein, a polymer-assisted cation solvation-confinement strategy is presented to enhance both water retention and the electrochemical window of poly(acrylamide-hydroxypropyl acrylate) (PAM-HPA) polyelectrolytes. Remarkably, PAM-HPA polyelectrolytes, without any organic additives, exhibit no water evaporation after over 3.5 months of air exposure at room temperature. Owing to the strong confinement toward H₂O in PAM-HPA polyelectrolyte, activated carbon-based aqueous symmetric MSCs achieve a record-breaking voltage of 2.5 V and the highest areal energy density of 187.9 µWh cm^-2 among all reported pure aqueous carbon-based MSCs. Even coupling with low-voltage MXene-based microelectrodes, the microdevice still maintains a high voltage exceeding 2 V, a significant areal energy density, and an ultra-long cycle life. Impressively, after exposing PAM-HPA polyelectrolytes to an oven at 60 °C for 24 h, the constructed MSCs retain nearly 90% of their capacitance compared to non-heat-treated polyelectrolytes. This work introduces a novel approach for developing non-drying polyelectrolytes with a wide electrochemical window, boosting the development of high-performance and safe micro-power sources.