A high temperature ammonia treatment was applied to carbon felt electrodes to enhance vanadium redox flow battery (VRFB) performance. Samples were heated to 900 °C in the presence of ammonia gas for up to 4 h. While all heating times resulted in an overall improvement in current density at 80% voltage efficiency, samples treated for 4 h showed the greatest increase in current density (325%) compared to untreated carbon felt. Raman spectroscopy showed a 74% increase in edge sites as a result of the 4 h treatment. Electrochemical surface area increased by 142% and scanning electron microscopy showed the appearance of pores on felt fiber surfaces, indicating that the performance improvement may be due to enhanced surface area in addition to functionalization. Impedance spectroscopy showed decreased charge transfer resistance and increased durability (during cycling) compared to other published electrode treatments. These results indicate that heated ammonia can be used to increase the performance of electrodes for vanadium flow battery applications, with excellent durability.