Single-Atom Co–N₄ Electrocatalyst Enabling Four-Electron Oxygen Reduction with Enhanced Hydrogen Peroxide Tolerance for Selective Sensing

Abstract

Electrocatalysis of the four-electron oxygen reduction reaction (ORR) provides a promising approach for energy conversion, storage, and oxygen monitoring. However, it is always accompanied by the reduction of hydrogen peroxide (H₂O₂) on most employed catalysts, which brings down the electrocatalytic selectivity. Here, we report a single-atom Co-N₄ electrocatalyst for the four-electron ORR at an onset potential of 0.68 V (vs RHE) in neutral media while with high H₂O₂ tolerance, outperforming commercial Pt electrocatalysts. Electrochemical kinetic analysis confirms that the Co-N₄ catalytic sites dominantly promote the direct four-electron pathway of the ORR rather than the two sequential two-electron reduction pathways with H₂O₂ as the intermediate. Density functional theory calculations reveal that H₂O₂ reduction is hampered by the weak adsorption of H₂O₂ on the porphyrin-like Co centers. This endows the electrocatalyst with improved resistance to current interference from H₂O₂, enabling highly selective O₂ sensing as validated by the reliable sensing performance in vivo. Our study demonstrates the intriguing advantage of single-atom catalysts with high capacity for tailoring metal-adsorbate interactions, broadening their applications in environmental and life monitoring.