Remarkable electrochemical performance of holey MXene/graphene hydrogel-based supercapacitor operated at − 60 °C in sulfuric acid aqueous electrolyte

The ability to store and deliver electricity quickly at low temperatures is crucial for exploring unknown spaces under harsh conditions. In this work, we present a supercapacitor with excellent high power density and ultra-low temperature tolerance. The supercapacitor is assembled using designed MXene/holey graphene hydrogel electrodes and an all-around 37.0% H₂SO₄ electrolyte. It combines high ionic conductivity, self-supporting properties, and anti-freezing ability. The optimal composition ratio of the supercapacitor demonstrates a power density of 2500 μW cm⁻² and an energy density of 64.86 μWh cm⁻², along with a high specific areal capacitance of 467 mF cm⁻² and excellent cycle stability, retaining 90.23% of its capacitance after 20,000 cycles. The electrochemical stability can be maintained even at temperatures as low as − 40 °C (with a retention rate of approximately 71.08%) and − 60 °C (with a retention rate of approximately 60.11%). Additionally, the device exhibits outstanding cycle stability, with a capacitance retention rate of over 95% after 20,000 cycles at − 60 °C. This study provides an opportunity to develop acid supercapacitors as environmentally tolerant energy storage devices.