<p>The application of environmentally friendly and renewable biomass materials as precursors for supercapacitor electrode materials has attracted much attention in recent years. Herein, we designed a KHCO₃-based pore regulation strategy to synthesize sunflower seed hull (SSH) into oxygen-rich interconnected porous activated carbon (SSHK) and reveal their structure–activity relationship with electrochemical performance. The samples produced at 800 °C for 2 h (SSHK-800–2) showed outstanding electrochemical performance with high specific capacitance (180.2 F g⁻¹) and good rate capability (83%), owing to the possible synergistic effects originating from their high specific surface area (1623.97 m² g⁻¹) and O-rich content. The SSHK-800–2-based symmetric supercapacitor delivered an impressive energy density of 15 Wh kg⁻¹ at a power density of 500 W kg⁻¹ and recorded 110% cycling stability after 10,000 cycles. SSH can be used as an efficient carbon precursor for electrode material in practical supercapacitors and this work offers an efficient, affordable, and environmentally friendly strategy for potential renewable energy storage devices.</p> Graphical Abstract <p></p>