Iron Porphyrins Embedded into a Supramolecular Porous Organic Cage for Electrochemical CO₂ Reduction in Water

Abstract

A porous organic cage composed of six iron tetraphenylporphyrins was used as a supramolecular catalyst for electrochemical CO -to-CO conversion. This strategy enhances active site exposure and substrate diffusion relative to the monomeric catalyst, resulting in CO generation with near-quantitative Faradaic efficiency in pH 7.3 water, with activities reaching 55 250 turnovers. These results provide a starting point for the design of supramolecular catalysts that can exploit the properties of the surrounding matrix yet retain the tunability of the original molecular unit.

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

“…These values are in the range observed for other molecular catalysts adsorbed onto heterogeneous supports in a similar manner . Co‐PB‐1(6) exhibits the largest percentage of EA Co , which agrees with our previous studies suggesting that the porosity enhances active site exposure . Co‐rPB‐1(6) has the lowest percentage of EA Co , which we attribute to the loss in porosity after imine reduction observed by gas sorption and MD.…”

“…This strategy has been used to synthesize binding sites in a POC for molecular recognition and for constructing POCs capable of hydrogen isotope separation . Of particular interest to our electrocatalysis program in water is the development of a porphyrin POC that is resistant to hydrolytic decomposition, which we have used to create a porous iron porphyrin catalyst for CO 2 reduction where the permanent porosity increases the density of electrochemically‐active sites for catalysis as well as transport of gaseous substrates and products …”

“…Furthermore, 1 H NMR spectroscopy shows the disappearance of the imine peak and subsequent broadening of the remaining resonances, which we attribute to a large degree of conformational heterogeneity (See Supporting Information). Using analogous methods to our previous work, cobalt was introduced into all six porphyrin moieties in both PB‐1(6) and rPB‐1(6) by heating with CoCl 2 and 2,6‐lutidine in THF (Scheme ). MALDI‐MS and UV/Vis show complete metalation for each catalyst (Figures S3–S4, S6–S10).…”

“…The Co III /Co II wave for Co‐TPP is irreversible, whereas Co‐PB‐1(6) and Co‐rPB‐1(6) display broadened re‐oxidation waves, and at slow scan rates more minor redox features are observable, suggesting a distribution of closely related active sites in the catalyst films. Analysis of the scan rate dependence of the Co III /Co II reduction waves yields the number of electrochemically active cobalt centers (EA Co ) in each heterogeneous film . For Co‐TPP, Co‐PB‐1(6), and Co‐rPB‐1(6), the observed EA Co were 6.3 nmol cm −2 , 9.1 nmol cm −2 , and 4.2 nmol cm −2 , respectively.…”

Positive Allosteric Control of Guests Encapsulation by Metal Binding to Covalent Porphyrin Cages

“…Porphyrins are attractive as active components for artificial allosteric systems due to their involvements in many biological processes through their binding, redox or photophysical properties. Especially, structures incorporating metalloporphyrins with a defined binding pocket have shown molecular recognition properties and catalytic activity …”