Dimethyl sulfoxide (DMSO) was added to an aqueous-based Na2SO4-polyacrylamide (PAM) electrolyte to improve its low temperature performance. The addition of DMSO significantly enhanced the ionic conductivity of Na2SO4-PAM binary electrolyte at sub-zero temperatures, while virtually maintained their excellent properties at and above ambient temperature. The improvement in low temperatures was correlated to the lower melting point and smaller crystal hydrates at freezing point. Solid capacitor cells using carbon nanotube electrodes with the ternary Na2SO4-PAM-DMSO electrolytes were assembled and compared against the binary Na2SO4-PAM baseline. Under ambient conditions, both cells showed similarly wide 1.8 V window and excellent rate capability. While the cells with binary electrolytes showed pure resistive behaviour at -20 °C, those with ternary electrolytes showed significant improvement in their capacitive voltammogram profile and impedance spectra. The results showed that DMSO can be effective in widening the operating temperature of neutral pH polymer electrolytes and their enabled solid capacitive devices.