Mechanistic Insights for Low-Overpotential Electroreduction of CO₂ to CO on Copper Nanowires

Abstract

Recent developments of copper (Cu)-based nanomaterials have enabled the electroreduction of CO 2 at low overpotentials. The mechanism of low-overpotential CO 2 reduction on these nanocatalysts, however, largely remains elusive. We report here a systematic investigation of CO 2 reduction on highly dense Cu nanowires, with the focus placed on understanding the surface structure effects on the formation of *CO (* denotes an adsorption site on the catalyst surface) and the evolution of gas-phase CO product (CO(g)) at low overpotentials (more positive than −0.5 V). Cu nanowires of distinct nanocrystalline and surface structures are studied comparatively to build up the structure−property relationships, which are further interpreted by performing density functional theory (DFT) calculations of the reaction pathway on the various facets of Cu. A kinetic model reveals competition between CO(g) evolution and *CO poisoning depending on the electrode potential and surface structures. Open and metastable facets such as (110) and reconstructed (110) are found to be likely the active sites for the electroreduction of CO 2 to CO at the low overpotentials.

An overview of Cu-based heterogeneous electrocatalysts for CO2reduction

“…Some groups [68][69][70][71]142,143 suggest that grain boundaries are the active sites. Some groups 80,144,145 believe that low-coordinated atoms act as active sites. There are also many groups 85,114,[146][147][148] which believe that the active phase is metallic Cu 0 since there is a signicant driving force for Cu 2 O reduction under CO 2 reduction conditions.…”

“…(100) and (211)) on the surface. Later studies by C. Wang, T. Mueller and co-workers 144,145 further suggested that the high activity and selectivity of the ECR nanowires could be ascribed to the (110) surface, high-angle grain boundaries, or some closely related metastable surface feature. Pre-reduction of annealed Cu in different solutions led to different activities, as also reported by J. J. Zhang's group.…”

Hydrogen bonding steers the product selectivity of electrocatalytic CO reduction

“…Most research to date has focused on understanding how the chemical composition and the surface morphology of the electrode give rise to catalytic reactivity. For example, quantitative correlations have been established between catalytic selectivity and grain-boundary density (19)(20)(21)(22), strain (23,24), Cu nanocluster size (25)(26)(27), edge-site density (28)(29)(30), or singlecrystal orientation (30)(31)(32). These observations have provided deep insights into the interactions of key reaction intermediates, such as CO, with the electrode surface and how these interactions impact product selectivity.…”

Heterogeneous catalysts for catalytic CO2 conversion into value-added chemicals

“…To tune selectivity, nano-structured Cu electrodes were studied, including Cu nanofoams [155], Cu nanowires [156][157][158][159][160], nanoporous Cu film [161], Cu nanocubes [151][152][153], Cu truncated nanocubes [153], Cu rhombic dodecahedrons [153], inverse opal Cu film [162], mesoporous Cu film [163], electro-redeposited Cu [164], electrodeposited Cu dendrites [165], prism shaped Cu [166], nano-structured Cu by battery cycling [150], hierarchical Cu pillar electrode [167], oxide derived Cu [160,[168][169][170]. The best CO 2 RR performance on Cu electrode was 60~70% faraday efficiency toward C 2 H 4 production [170,171].…”