Supramolecular Porphyrin Cages Assembled at Molecular–Materials Interfaces for Electrocatalytic CO Reduction

Abstract

Conversion of carbon monoxide (CO), a major one-carbon product of carbon dioxide (CO2) reduction, into value-added multicarbon species is a challenge to addressing global energy demands and climate change. Here we report a modular synthetic approach for aqueous electrochemical CO reduction to carbon–carbon coupled products via self-assembly of supramolecular cages at molecular–materials interfaces. Heterobimetallic cavities formed by face-to-face coordination of thiol-terminated metalloporphyrins to copper electrodes through varying organic struts convert CO to C2 products with high faradaic efficiency (FE = 83% total with 57% to ethanol) and current density (1.34 mA/cm2) at a potential of −0.40 V vs RHE. The cage-functionalized electrodes offer an order of magnitude improvement in both selectivity and activity for electrocatalytic carbon fixation compared to parent copper surfaces or copper functionalized with porphyrins in an edge-on orientation.

In‐Situ Nanostructuring and Stabilization of Polycrystalline Copper by an Organic Salt Additive Promotes Electrocatalytic CO2 Reduction to Ethylene

“…[1][2][3][4] In the context of the electrochemical CO 2 reduction reaction (CO 2 RR), small molecule additives have been employed to tune the reactivity of heterogeneous catalysts by stabilizing intermediates,i nhibiting proton diffusion, or acting as redox mediators.F or example,o rganic species such as N-aryl pyridinium salts, [5] imidazole, [6][7][8] thiol [9] and cysteamine [10] have been reported to alter the surface of the electrode,y ielding catalytic systems with increased selectivities for specific products. [11,12] Germane to the present study,o ur research team disclosed as imple method for increasing the selectivity of CO 2 RR towards C !2 products by combining apolycrystalline copper electrode with an N-aryl pyridinium salt additive in bicarbonate aqueous solutions (Figure 1a). [5] Upon in situ electroreduction of these water-soluble additives,a no rganic film is deposited onto the electrode,a ltering the catalytic properties of the Cu surface.S elective inhibition of CH 4 and H 2 production was observed, resulting in an improved selectivity for C !2 products with Faradaic efficiencies (FE) higher than 60 %.…”

Tuning Gold Nanoparticles with Chelating Ligands for Highly Efficient Electrocatalytic CO2 Reduction

“…To understand how P1 contributes to the observed improvements of catalytic activity and selectivity,w ef irst investigated the electrochemically active surface area (ECSA) of both OAm-AuNP and P1-AuNP by aP bu nderpotential deposition (UPD) method (Figure 2d). [28,33,41,42] The calculated ECSA of P1-AuNP is 3.2-fold larger than that of OAm-AuNP,w hich is most likely due to more exposed Au sites as anticipated in ligand design. To further confirm this hypothesis,w ea lso acquired the ECSA of naked-AuNP.I t turns out that naked-AuNP and P1-AuNP possess comparable ECSA (1.17:1) and similar TEM pattern (Supporting Information, Figure S6), suggesting that both catalysts expose similar numbers of Au sites for CO 2 RR.…”

Multidentate Anchors for Surface Functionalization

“…(b) Schematic representation of the quadripodal porphyrin compound 12 on Cu electrode surface (Cu/ 12 ). Reprinted with permission from reference . Copyright 2017 American Chemical Society.…”

“…Recently, Chang et al. report the assembly of the thiol‐terminated metalloporphyrin 12 on copper electrode to yield supramolecular cages on the surface (Figure b) . The four flexible arms of 12 are placed on the ortho ‐position of meso ‐phenyl rings in order to immobilize the complex in a planar orientation.…”

“…[68] Recently,C hang et al report the assembly of the thiol-terminated metalloporphyrin 12 on copper electrode to yield supramolecular cages on the surface (Figure 5b). [69] The four flexible arms of 12 are placed on the ortho-position of meso-phenyl rings in order to immobilize the complex in ap lanar orientation. As tructurally relatedp orphyrin compound with the flexible arms in the para-position of meso-phenyl rings was used to achieve an edge-on orientation for the purpose of comparison study.T he obtained Cu/12 materials show an order of magnitude improvement in the selectivity and activity for the electrochemical CO reduction, compared to free copper surfaces or those functionalized with porphyrins in the edge-on orientation.…”