Electron-trapping feature on SL-HC-CN for efficient oxygen reduction

Photocatalytic hydrogen peroxide (H₂O₂) production offers a green and sustainable pathway to replace the energy-intensive anthraquinone process. Highly crystalline semiconductors with long-range structural order and reduced phase defects enable efficient charge carrier separation and diffusion, essential for superior photocatalytic activity. This study proposes a K⁺ eutectic-guided, programmed thermally-controlled stripping strategy to successfully synthesize highly crystalline single-layer carbon nitride (SL-HC-CN) nanosheets. Research reveals that K⁺ ions play a pivotal role in guiding structural ordering and expanding the π-conjugated system. This not only enhances electron mobility but also forms stable surface electron-trapping states, manifesting as reversible blue photochromic behavior. These capture states accumulate and store photo-generated electrons, prolonging their lifetime and facilitating efficient electron transfer to O₂, generating ·O₂^- and *OOH intermediates. Concurrently, K⁺-induced local electrostatic fields stabilize critical intermediates, suppressing disproportionation and reverse reactions, thereby significantly enhancing the selectivity of the 2e^- oxygen reduction reaction (ORR) and H₂O₂ yield. Compared to Na⁺-templated and bulk CN, K⁺-engineered SL-HC-CN exhibits broadened visible light absorption, enhanced charge separation efficiency, and superior H₂O₂ synthesis performance. This study reveals the crucial role of cation specificity in regulating crystallinity, electron trapping, and reaction pathways, providing new insights for designing highly efficient, selective metal-free photocatalysts.