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

The electrochemical performance of aqueous electrolytes at low temperatures is frequently suboptimal due to their low freezing point (0 degrees 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 degrees C. PVA/CNF-H2SO4-based solid-state supercapacitors (C7-SSC) demonstrate a capacitance of up to 813 mF cm(-2) at -50 degrees 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 mu Wh cm(-2) and 0.4 mu W cm(-2) at -50 degrees 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.