Hydrogen bond crosslinking hydrogel for high-performance ultra-low temperature MXene-based solid state supercapacitors

Abstract

The electrochemical performance of aqueous electrolytes at low temperatures is frequently suboptimal due to their low freezing point (0 °C). In this study, we constructed MXene-based ultra-low temperature polyvinyl alcohol/nanocellulose-H2SO4 (PVA/CNF-H2SO4) hydrogel electrolytes utilising hydrogen bonding between water molecules and nanocellulose. The process results in a reduction in the amount of free water present in the hydrogel electrolyte, lowering its freezing point to -77.35 °C. PVA/CNF-H2SO4-based solid-state supercapacitors (C7-SSC) demonstrate a capacitance of up to 813 mF cm-2 at -50 °C, exhibiting high-rate performance at low temperatures. The capacitance remains at 45 F g-¹ at a current density of 20 A g-¹. The maximum areal energy and power densities of our C7-SSC achieve 113 μWh cm-² and 0.4 μW cm-² at -50 °C, respectively, surpassing the majority of state-of-the-art devices. This work provides new insights into MXene-based hydrogel manufacturing and expands the range of potential applications for such materials.