Mesoporous carbon nitride supported 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine cobalt(ii) as a selective and durable electrocatalyst for the production of hydrogen peroxide via two-electron oxygen reduction

Abstract

Mesoporous carbon nitride (MCN) is synthesized using a mesoporous silica material (MCM-41) as a sacrificial template. 5,10,15,20-Tetrakis(4-methoxyphenyl)-21H,23H-porphine cobalt(II) (cobalt tetramethoxyphenylporphyrin, CoTMPP), which consists of methoxy groups as the electron-rich center is integrated with MCN and the resulting composite material (CoTMPP@MCN) without any further heat treatment is used for the electrocatalytic reduction of oxygen. CoTMPP@MCN shows a higher onset potential (0.65 and 0.84 V, respectively, in 0.1 M HClO₄ and 0.1 M KOH) for the oxygen reduction reaction (ORR) than the bare MCN (0.34 and 0.60 V, respectively, in 0.1 M HClO₄ and 0.1 M KOH). The ORR onset potential exhibited by CoTMPP@MCN is comparable to several non-pyrolyzed mono-nuclear metal porphyrin integrated on carbon-based supports in both acidic and basic media. Kinetic measurements of CoTMPP@MCN show high selectivity for two-electron oxygen reduction to H₂O₂ in both media. The H₂O₂ yield in terms of faradaic efficiency is measured to be 87.6 and 89.0%, respectively, in 0.1 M HClO₄ and 0.1 M KOH. CoTMPP@MCN exhibits amazingly high durability (minute changes in the onset potential and current density at high reduction potentials after 3000 CV cycles) facilitated by the surface coordination of CoTMPP through the nitrogen present on the MCN surface. Being highly selective and outstandingly durable, CoTMPP@MCN fulfills all necessary requirements for an economically efficient electrocatalyst for industrial hydrogen peroxide synthesis and related commercial applications.