<p>In the context of mounting energy demands and escalating environmental pollution, the development of high-efficiency, low-temperature-tolerant supercapacitors has emerged as a pivotal research focus in the domain of energy storage. To address the limitations of conventional supercapacitors, which include low energy density and poor electrochemical performance at low temperatures, this study proposes a three-dimensional hierarchical porous nitrogen-doped graphene/carbon nanotube composite hydrogel (NGM) electrode. The NGM was synthesized by reducing graphene oxide (GO) and carboxylated multi-walled carbon nanotubes (MWCNTs) using urea as both a reducing agent and nitrogen source. Electrochemical characterization demonstrates that the NGM5 electrode (with optimal nitrogen doping) exhibits enhanced power density and low-temperature adaptability, achieving a remarkable areal specific capacitance of 498 mF cm⁻² at 1&#xa0;mA&#xa0;cm⁻² and an energy density of 63.91 µWh cm⁻² at 5000&#xa0;µW&#xa0;cm⁻², outperforming comparable studies. When tested with a 37 wt% H₂SO₄ electrolyte, the supercapacitor retains 62.01% and 50.67% of its capacitance at − 40&#xa0;°C and − 60&#xa0;°C, respectively. Furthermore, after 8000 cycles at 25&#xa0;°C and − 60&#xa0;°C, the device exhibits capacitance retention rates of 74.75% and 70.29%, respectively, underscoring its remarkable low-temperature tolerance and cycling stability. This work represents a significant advancement in the development of wide-temperature-range, high-power-density supercapacitors, with promising applications in wearable devices, electric vehicles, and energy storage under extreme conditions.</p>