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

Abstract

Bridging homogeneous molecular systems with heterogeneous catalysts is ap romising approach for the development of new electrodes,c ombining the advantages of both approaches.I nt he context of CO 2 electroreduction, molecular enhancement of planar copper electrodes has enabled promising advancement towards high Faradaic efficiencies for multicarbon products.B esides,n anostructured copper electrodes have also demonstrated enhanced performance at comparatively low overpotentials.H erein, we report an ovel and convenient method for nanostructuring copper electrodes using N,N'-ethylene-phenanthrolinium dibromide as molecular additive.Selectivities up to 70 %for C !2 products are observed for more than 40 hw ithout significant change in the surface morphology.M echanistic studies reveal several roles for the organic additive,including:the formation of cubelike nanostructures by corrosion of the copper surface,t he stabilization of these nanostructures during electrocatalysis by formation of ap rotective organic layer,a nd the promotion of C !2 products.

Molecular enhancement of heterogeneous CO2 reduction

“…It has been proposed that organic additives or coatings, such as cysteamine 19 , thiols 19,20 , amine 20,21 , polypyrrole 22 , N-heterocyclic carbenes (NHCs) 23 , 4-pyridylethylmercaptan (4-PEM) 24 , glycine 25 and N-substituted tetrahydro-bipyridine 26,27 , may control the binding energy of CO 2 RR intermediates such as *COOH, *CO and *HCOO ( Fig. 2a).…”

“…Surface reorganization during electrocatalysis can affect CO 2 RR selectivity. Molecular additives and coatings may serve as ligands to stabilize the surface of the electrode against severe reconstruction 27 (Fig. 4i).…”

Report of the Basic Energy Sciences Roundtable on Liquid Solar Fuels

“…The strategies employed to increase selectivity include varying the pH and composition of the electrolyte, increasing the surface area and altering the surface structure of the catalyst through nano-and mesostructuring, chemically modifying the surface with molecular additives, and integrating the catalyst into a gas-diffusion electrode that increases the flux of CO 2 to the surface ( Figure S10). These studies have allowed for a steady improvement in product selectivity for multi-carbon products from 34% 65 to greater than 70% 66 . Depending on the catalyst, these selectivity improvements can result from an increase in the rate of formation of multi-carbon products; an inhibition in the rate of formation of methane, hydrogen, and CO; or both.…”

“…For example, N,N′-ethylenephenanthrolinium dibromide promotes restructuring of the copper surface into cube-like nanostructures, which are known to have product ratios distinct from those of polycrystalline copper. In parallel, the reductive coupling product of this additive stabilizes the nanostructures formed and likely influences binding of key CO intermediates through a mechanism similar to N-substituted arylpyridinium salts 66 . To fully exploit the beneficial effects of molecular additives to optimize product selectivity and enhance catalyst durability, their mechanisms of action must be fully understood.…”

Improved electrochemical conversion of CO2 to multicarbon products by using molecular doping

“…Alternatively, molecular engineering of either the electrolyte or the catalyst surface has recently been proposed for orienting the selectivity of the reaction by stabilizing intermediates, inhibiting proton diffusion, or acting as redox mediators during the electrochemical CO 2 reduction reaction (CO 2 RR) 26 – 30 . Organic species such as N-aryl pyridinium salts 31 , 32 , imidazole 33 – 35 , thiol 36 , 37 , and cysteamine 38 have been reported as an effective lever to tune the reaction selectivity toward the formation of specific products by stabilizing key reaction intermediates. Functionalization of alkyl chains can also lead to better CO 2 RR performance by suppressing the competitive hydrogen evolution reaction (HER) via the creation of hydrophobic regions on the surface of the catalyst 37 , 39 , 40 .…”