<p>While bismuth oxyformate (BiOCOOH) is known to be a promising pseudocapacitive material for supercapacitors, its poor electrical conductivity, low surface area and cyclic stability continue to hinder its practical applications. Here we report the first ternary integration of BiOCOOH nanospheres with nitrogen-enriched graphitic carbon nitride (g-C₃N₅) nanosheets and acid-functionalised multi-walled carbon nanotubes (MWCNTs) into a hierarchical nanocomposite via a facile solvothermal method. Three specific innovations distinguish this work: First, the use of g-C₃N₅ (confirmed by X-ray photoelectron spectroscopy (XPS) N 1s analysis) rather than the conventional graphitic carbon nitride (g-C₃N₄) provides a nitrogen-richer, more electrochemically active scaffold. Second, systematic kinetic analysis confirms a mixed pseudocapacitive charge-storage mechanism (b-value = 0.647; surface-capacitive contribution increasing from 43% at 10 mV s^− 1 to 63% at 50 mV s^− 1). Third, the ternary architecture reduces the charge-transfer resistance by more than 90% relative to pure BiOCOOH (from &gt; 22,000 Ω to 1,834 Ω), as confirmed by electrochemical impedance spectroscopy (EIS). The composite delivers a specific capacitance of 419&#xa0;F g^− 1 at 0.5&#xa0;A g^− 1 by the linear galvanostatic charge-discharge (GCD) method, a 5.4-fold improvement over bare BiOCOOH and retains 92% capacitance over 1000 cycles. When assembled as a BiOCOOH/g-C₃N₅/MWCNT // activated carbon asymmetric coin-cell device, a specific cell capacitance of 63.3&#xa0;F g^− 1 at 1&#xa0;A g^− 1 and a peak energy density of 28.49 Wh kg^− 1 at 900&#xa0;W kg^− 1 are achieved, with 13.43 Wh kg^− 1 retained at 2250&#xa0;W kg^− 1. These findings demonstrate the viability of BiOCOOH/g-C₃N₅/MWCNT nanoarchitecture as a promising, cost-effective, and active electrode material for future-generation pseudocapacitive energy storage devices.</p>