Metal-free carbon catalysts are promising alternatives to noble-metal electrocatalysts for H₂O₂ production through two electron oxygen reduction reaction (2e⁻ ORR). Herein, a novel bioengineering approach is proposed to prepare N-doped hollow carbon nanoboxes from guanine precursor. The optimized NC-HNBs-550 exhibits an exceptional electrocatalytic performance, achieving a high H₂O₂ Faradaic efficiency (FE) of over 90% across a broad potential window exceeding 0.6 V. Remarkably, when tested in a flow cell configuration, NC-HNBs-550 delivers near-unity FE for H₂O₂ production at industrial-grade current densities, demonstrating its practicality for scalable applications. Impressively, the in situ electro-synthesized H₂O₂ is further employed as a green oxidant for rapid degradation of various organic dyes and even tetracyclines, and high-purity benzoyl peroxide (BPO) synthesis, highlighting its versatility in environmental and chemical applications. Combining experimental and theoretical analyses, we reveal that the superior 2e⁻ ORR activity originates from the abundance of pyrrolic-N species in NC-HNBs, which optimize the adsorption energy of *OOH intermediates and promote selective O₂ reduction. This work not only advances the rational design of biomass-derived carbon catalysts for sustainable H₂O₂ production but also provides a versatile platform for environmental remediation and value-added chemical production.