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 H 2 O 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.