Supramolecular Tuning Enables Selective Oxygen Reduction Catalyzed by Cobalt Porphyrins for Direct Electrosynthesis of Hydrogen Peroxide
We report a supramolecular design strategy for promoting the selective reduction of O2 for direct electrosynthesis of H2O2. Specifically, we utilized cobalt tetraphenylporphyrin (Co-TPP), a non-selective oxygen reduction reaction (ORR) catalyst, 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 porous 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, and we attribute this high selectivity to site isolation of the discrete molecular units, as the analogous Co-TPP monomer generates only a 50% mixture of H2O2 and H2O from electrochemical ORR under the same conditions. 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.