Boosting the performance of electrical double layer capacitors (EDLCs) without degradation of power density or lifespan demands innovative modification of electrode materials in order to have both sufficient surface area and fast ion diffusion kinetics. Herein, carbon nanofibers (CNFs) with a unique hetero-shaped mesoporous structure were reported via decomposition of poly (methyl methacrylate) (PMMA) and dissolution of ZnO nanoparticles during the carbonization process. To optimize electrochemical performance, the amount of ZnO nanoparticles was varied from 0 to 0.5, 1.5, or 2.5 wt%. As a result, hetero-shaped mesoporous CNFs with 1.5 wt% ZnO nanoparticles (1.5ZnO-PCNF) exhibited the largest surface area of 691.6 m² g^-1, providing sufficient electrochemical active sites. Moreover, 1.5ZnO-PCNF showed the highest mesopore volume fraction of 92.5%, leading to fast ion diffusion kinetics. The optimized 1.5ZnO-PCNF electrode showed a specific capacitance of 120 F g^-1 at a current density of 0.2 A g^-1, 91.6% capacitance retention at a current density of 2 A g^-1, and excellent cycling stability up to 3,000 cycles (maintaining 75.8% of capacitance after 3,000 cycles). These improvements in performance were mainly attributed to a well-generated hetero-shaped mesoporous structure with a large specific surface area

Keywords: Electrical double layer capacitors, Carbon nanofibers, hetero-shaped mesopore, cycling stability, rate performance