Supramolecular Tuning Enables Selective Oxygen Reduction Catalyzed by Cobalt Porphyrins for Direct Electrosynthesis of Hydrogen Peroxide

Abstract

We report a supramolecular strategy for promoting the selective reduction of O2 for direct electrosynthesis of H2O2. We utilized cobalt tetraphenylporphyrin (Co‐TPP), an oxygen reduction reaction (ORR) catalyst with highly variable product selectivity, as a building block to assemble the permanently porous supramolecular cage Co‐PB‐1(6) bearing six Co‐TPP subunits connected through twenty‐four imine bonds. Reduction of these imine linkers to amines yields the more flexible cage Co‐rPB‐1(6). Both Co‐PB‐1(6) and Co‐rPB‐1(6) cages produce 90–100 % H2O2 from electrochemical ORR catalysis in neutral pH water, whereas the Co‐TPP monomer gives a 50 % mixture of H2O2 and H2O. Bimolecular pathways have been implicated in facilitating H2O formation, therefore, we attribute this high H2O2 selectivity to site isolation of the discrete molecular units in each supramolecule. The ability to control reaction selectivity in supramolecular structures beyond traditional host–guest interactions offers new opportunities for designing such architectures for a broader range of catalytic applications.

Metal–Organic‐Framework‐Supported Molecular Electrocatalysis for the Oxygen Reduction Reaction

“…We herein report MOF‐supported Co porphyrins as catalysts for oxygen electrocatalysis. Co porphyrins are active and robust for electrocatalytic ORR, which is a significant process in many new energy conversion technologies, including fuel cells and metal–air batteries [34–41] . Through ligand exchange, [42–45] we can graft Co porphyrins on MOF surfaces (Figure 1 c), considering the following benefits of using MOFs as supports [46–53] .…”

Metal–Organic‐Framework‐Supported Molecular Electrocatalysis for the Oxygen Reduction Reaction

“…Co porphyrins are active and robust for electrocatalytic ORR, which is a significant process in many new energy conversion technologies, including fuel cells and metal-air batteries. [34][35][36][37][38][39][40][41] Through ligand exchange, [42][43][44][45] we can graft Co porphyrins on MOF surfaces (Figure 1 c), considering the following benefits of using MOFs as supports. [46][47][48][49][50][51][52][53] First, with different metals and organic linkers, the compositions of MOFs can be modified to make diverse hybrids.…”

Design Strategies of Non‐Noble Metal‐Based Electrocatalysts for Two‐Electron Oxygen Reduction to Hydrogen Peroxide

“…The reaction selectivity can be finely controlled in supramolecular structures. Using cobalt tetraphenylporphyrin (Co‐TPP) as the building block, porous supramolecular cage Co‐PB‐1(6) bearing six Co‐TPP subunits connected by 24 imine bonds was obtained [128] . The Co‐rPB‐1(6) was yielded by the reduction of the imine linkers to amines, which is a more flexible and electron‐rich supramolecular catalyst (Figure 7a).…”