Electrochemical two-electron O2 reduction reaction toward H2O2 production: using cobalt porphyrin decorated carbon nanotubes as a nanohybrid catalyst

Abstract

Electroreduction of O₂ into H₂O₂ holds great promise to replace the energy-intensive anthraquinone process that is currently used as an industry standard, but its practical feasibility still requires materials with high catalytic efficiencies. It is now shown that a Co-tetramethoxyphenylporphyrin–carbon nanotube (CoTMPP/CNT) nanohybrid acts as a high-performance catalyst with fast electron delivery to active sites toward electrochemically generating H₂O₂ under acidic aqueous conditions, achieving a H₂O₂ selectivity of over 95% and achieving strong stability. More impressively, it reduces O₂ to H₂O₂ with an unprecedented mass activity of 9694 A g⁻¹ and a high turnover frequency of up to 6.95 s⁻¹ (0.6 V_RHE), representing the most active molecule-based two-electron O₂ reduction reaction (ORR) electrocatalyst under an acidic environment so far. It also performs efficiently in neutral media. Taking advantage of the well-defined structure of the TMPP unit, we systematically study the trends in catalytic activity as well as selectivity toward the ORR at the M–N₄ site (M = Mn, Fe, Co, Ni, Cu) with an identical chemical environment of TMPP. In situ attenuated total reflection infrared spectroscopy and density functional theory calculations were used to reveal further the catalytic mechanism.