Polygonal carbon nanofibers (PCNFs) were prepared at large scale by chemical vapor deposition using Ni3Sn2 intermetallic compound as a catalyst. The PCNFs feature a polygonal cross-section with side lengths ranging from 200 nm to 400 nm, as primarily determined by the orthorhombic structure of the Ni3Sn2 compound. The PCNFs were subsequently activated by KOH with different concentrations, denoted as a-PCNFs, for supercapacitor electrode applications. The PCNFs were significantly etched during the activation process under a high KOH concentration, forming a unique thin-ribbon-like nanostructure with large specific surface area and high content of oxygen-containing functional groups. The electrochemical measurements reveal that a-PCNFs, activated by KOH at a KOH:C weight ratio of 4:1 under 800 ℃, exhibit favorable electrochemical properties with a specific capacitance of 186 F g-1 at a current density of 3 A g-1 in 1 M Na2SO4, good rate capability (capacitance retention of 81.9% at a current density of 10 A g-1), low internal resistance, and reasonably good cycle stability with a capacitance retention of 85.2% after 1000 cycles. These promising electrochemical properties coupled with high yield indicate significant potential for use as scalable supercapacitor electrodes.