Redox flow batteries, especially the vanadium redox flow battery (VRFB), are promising candidates for grid-scale applications. Operating temperature significantly affects the power, efficiency, and energy rating of a flow battery. Operating a VRFB at sub-zero temperatures leads to significant energy loss due to increased resistance for the electrochemical reactions. In the present work, the role of thermal activation on the electrodes was studied as a possible remedial measure. Thermal activation modifies the carbon felt electrode surface properties, which helps in restoring the kinetic reversibility even at low-temperature operation. To this end, the electrodes were pyrolyzed in the air at temperatures of 350 to 450 °C for 30 hours. Post-treatment characterization showed activation at 400 °C to be optimal. Electrochemical testing of a large-scale (936 cm²) VRFB at two different temperatures, viz., 10 and 0 oC showed thermal activation effectively reduces the VRFB system temperature sensitivity. Around 14% improvement in energy efficiency was achieved through the thermal activation of electrodes at an operating temperature of 0 %C.