Electron‐Deficient Cu Sites on Cu₃Ag₁ Catalyst Promoting CO₂ Electroreduction to Alcohols

Abstract

carbon sources through different technical routes, [1] which either have negative environmental impacts or deliver a poor atomic economy while being energy intensive. [2] For instance, the life-cycle greenhouse gas emission for producing a liter of bioethanol is ≈1.6 kg CO 2 equivalent. [3] For fuel ethanol with a global production of ≈104 billion liters per year, [4] the annual CO 2 emission is more than 170 million metric tons, corresponding to 0.5% of the global annual overall carbon emission. [5] New technologies are thus in demand to balance the target of environmental protection and economic development. Electrochemical CO 2 reduction (ECR) driven by renewable energies is a competitive candidate, as it converts CO 2 into liquid products like formate and alcohols with nearly net-zero CO 2 emissions. [6] Nonetheless, the Faradaic efficiency (FE) for CO 2-to-alcohol production generally remains low, typically less than 50%. [7] For instance, Gewirth and co-workers presented a nanoporous Cu-Ag alloy for the enhancement of ECR activity, with an FE toward ethanol of ≈25%. [8] Bell and co-workers reported a Cu-Ag alloy with stain effect, and the total FE of alcohol production was less than 15%. [9] Recently, Sargent and co-workers reported an enhancement of ethanol selectivity in a flow cell system by tuning binding site diversity in an Ag/ Cu catalyst, while the FE for ethanol was still less than 50%. [10] The challenge in developing effective strategies of tuning the energetics of reaction pathways limits the CO 2-to-alcohol selectivity. Based on the theoretical and experimental studies, [11] ethylene (C 2 H 4) generally dominates the C 2+ product distribution, with a theoretical prediction of an alcohol/ethylene ratio of 35:65. [12] However, Calle-Vallejo and Koper reported that ethanol presents a lower free energy position compared to ethylene in the entire reaction route of carbon monoxide (CO) electroreduction to C 2 products. [13] The poor alcohol selectivity has been attributed to the unfavorable adsorption of key intermediates in the ethanol pathway on copper, [13] such as CH 3 CHO* and CH 3 CH 2 O* proved by Chorkendorff and co-workers. [14] Thus, it is rational to hypothesize that an enhanced alcohol selectivity may arise from modulating the adsorption of key intermediates like CH 3 CH 2 O* in the ECR pathways. In addition, it is also well known that Ag component can suppress hydrogen Copper-based catalysts electrochemically convert CO 2 into multicarbon molecules. However, the selectivity toward alcohol products has remained relatively low, due to the lack of catalysts favoring the adsorption of key intermediates in the alcohol pathways. Herein, a Cu 3 Ag 1 electrocatalyst is developed using galvanic replacement of an electrodeposited Cu matrix. The Cu 3 Ag 1 electrocatalyst enables a 63% Faradaic efficiency for CO 2-to-alcohol production and an alcohol partial current density of −25 mA cm −2 at −0.95 V versus reversible hydrogen electrode, corresponding to a 126-fold enhancement in selectivity and 25-...

Engineering Silver‐Enriched Copper Core‐Shell Electrocatalysts to Enhance the Production of Ethylene and C2+ Chemicals from Carbon Dioxide at Low Cell Potentials

“…The injection lasted 10 h and the mixture was stirred for an additional 12 h to ensure uniform growth of the Ag‐enriched shell. [ 69,70 ] The Cu Core and Cu@Ag NPs were collected by centrifugation, washed with hexane and methanol, and dispersed in hexane for further use. Figure 1b is a proposed atomic scheme for the formation of the Cu@Ag NPs through the process outlined in Figure 1a.…”

“…[ 57,58 ] One important solution to tune the electronic properties of Cu is to design bimetallic electrocatalysts that combine a noble metal with Cu (e.g., CuPd, CuAg, and CuAu). [ 49,59–70 ] CuAg bimetallic catalysts are particularly important and reported to have increased conductivity, stability, and local concentration of surface carbon monoxide species (CO*). [ 15,16,36,43,65–68,70 ] Research on CuAg catalysts often relies on large nanoparticles (NPs, >30 nm), likely due to the challenges for making bimetallic NPs between two immiscible metals, highlighting the synthetic need and importance for controlling the atomic ratio and nanostructures between Cu and Ag towards generating active sites.…”

Residual Chlorine Induced Cationic Active Species on a Porous Copper Electrocatalyst for Highly Stable Electrochemical CO2 Reduction to C2+

“…Theh eteroatomic doping in Cu matrix can induce the change in chemical state and electronic structure of Cu via electron transfer between Cu atoms and the doped atoms. [33] Non-metallic elements,i ncluding nitrogen and boron, have also been demonstrated to modify the electronic structure of Cu and induce positively charged Cu sites. [8a,26] Ther esidual Ii ons also promoted ah igh content of Cu + species in iodine-modified Cu catalyst after CO 2 RR.…”

Residual Chlorine Induced Cationic Active Species on a Porous Copper Electrocatalyst for Highly Stable Electrochemical CO2 Reduction to C2+

“…In this work, the Cl ions were found to be more stable than F ions in the e‐CuOHFCl electrocatalysts under CO 2 RR conditions and the residual Cl still existed after long‐term CO 2 RR test. The heteroatomic doping in Cu matrix can induce the change in chemical state and electronic structure of Cu via electron transfer between Cu atoms and the doped atoms [33] . Non‐metallic elements, including nitrogen and boron, have also been demonstrated to modify the electronic structure of Cu and induce positively charged Cu sites [8a, 26] .…”