Selective CO₂ Electroreduction to Ethylene and Multicarbon Alcohols via Electrolyte‐Driven Nanostructuring

Abstract

Production of multicarbon products (C2+) from CO2 electroreduction reaction (CO2RR) is highly desirable for storing renewable energy and reducing carbon emission. The electrochemical synthesis of CO2RR catalysts that are highly selective for C2+ products via electrolyte‐driven nanostructuring is presented. Nanostructured Cu catalysts synthesized in the presence of specific anions selectively convert CO2 into ethylene and multicarbon alcohols in aqueous 0.1 m KHCO3 solution, with the iodine‐modified catalyst displaying the highest Faradaic efficiency of 80 % and a partial geometric current density of ca. 31.2 mA cm−2 for C2+ products at −0.9 V vs. RHE. Operando X‐ray absorption spectroscopy and quasi in situ X‐ray photoelectron spectroscopy measurements revealed that the high C2+ selectivity of these nanostructured Cu catalysts can be attributed to the highly roughened surface morphology induced by the synthesis, presence of subsurface oxygen and Cu+ species, and the adsorbed halides.

Imaging electrochemically synthesized Cu2O cubes and their morphological evolution under conditions relevant to CO2 electroreduction

“…Interestingly, regardless of the initially exposed crystal facets, only {100} planes remained after exposing these crystals to Cl − -containing solutions for a few minutes, leading to cubic shapes. Moreover, the electrochemical nanostructuring of Cu foils into cubic facets was observed in the presence of Cl − , while flatter larger morphologies and needle-like structures were obtained when cycling in the presence of Br − and I − , respectively 44 . We also showed recently 8 that Cu cubes can be grown by electrodeposition on a carbon substrate (HOPG) using CuSO 4 as Cu source to create NPs and KCl to reshape them.…”

“…Even more importantly, the highest ethylene yield was obtained when the Cu NCs/Cu samples were pretreated with an oxygen plasma which lead to a drastic change in the structure and the loss of the cubic shape after reaction, while the same samples pretreated in Ar-plasma retained the cubic structure but resulted in a significantly lower C2-C3 product selectivity. In general, the loss of Cu(100) facets is correlated with a decrease in the yield of ethylene 9,44,47 , although other factors such as the content of subsurface oxygen or Cu(I) species have also been mentioned to play a role 9,48 . Unfortunately, correlating the observed structural transformations with their impact on reaction product selectivity is still a nontrivial technical challenge for LC-TEM, and outside the scope of this work.…”

Designing Electrolyzers for Electrocatalytic CO₂ Reduction

“…Due to their simple configuration and easy operation, H-cell electrolyzers are usually the first choice in mechanistic studies. While current densities are limited in H-cell electrolyzers, high selectivities towards target products that are often determined by intrinsic properties of catalysts have been reported in previous studies 55, [67][68][69] . For example, both formate and CO, two important C1 products, can be produced with high Faradaic efficiency of > 90% over Pd nanoparticles via engineering active phases and reaction pathways (Fig.…”

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

“…Increasing the oxidation state of copper has been suggested to improve the CO2RR performance and notably the formation of C2+ species 14,21,22 . Various strategies are being explored to prepare Cu + by using controlled oxidation via plasma treatments or doping with boron and halides 14,[23][24][25] . 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 CO2 reduction reaction (CO2RR) [26][27][28][29][30] .…”