Absence of Oxidized Phases in Cu under CO Reduction Conditions

Abstract

The surface structure and oxide content near the surface of copper electrodes under CO and CO 2 reduction conditions are debated. By live-monitoring Cu and Cu 2 O Bragg peaks from the surface of a polycrystalline Cu electrode while scanning from open-circuit potential to CO reduction potentials, we show that the near-surface region is fully converted to the metallic phase at approximately +0.3 V vs RHE.

On the Oxidation State of Cu2O upon Electrochemical CO2 Reduction: An XPS Study

“…On the one hand, the latter takes place at potentials ! 0 volts vs. the reversible hydrogen electrode (V RHE ) that are well below the Cu 2 O/Cu 0 equilibrium (at � 0.5 V RHE ), [11] and from which the operando reduction of the initial oxide would be expected -an extent that has been predicted by several computational studies [12,13] and experimentally demonstrated using in situ X-ray diffraction [14] and Raman spectroscopy, [10,15] as well as postmortem secondary ion mass spectrometry (SIMS). [16] On the other hand, and in clear conflict with those works, a greater number of recent studies implementing in situ or post-mortem X-ray absorption, photoelectron or electron energy loss spectroscopies (XAS, XPS, EELS) have concluded that the initial oxide does not get completely reduced in the course of the CO 2reduction process.…”

Optical Excitation of a Nanoparticle Cu/p-NiO Photocathode Improves Reaction Selectivity for CO2 Reduction in Aqueous Electrolytes

“…This electrochemical observation is consistent with recent in operando spectroscopic evidence of the electrocatalytically active phase of Cu-based cathodes. 72 We also note that a change in the 10 optical absorption was observed for these Cu/p-NiO films immediately after cyclic voltammetry was performed. The freshly cycled Cu/p-NiO photocathodes exhibit a new spectral feature located around 630 nm that we attribute to the surface plasmon resonance of metallic Cu nanoparticles (Figure 2c, red curve).…”

Structure‐Sensitivity and Electrolyte Effects in CO2 Electroreduction: From Model Studies to Applications

“…The possible active role of subsurface oxygen induced in the OD‐Cu copper structure has been focus of intense debate, and several authors have pointed out that both residual subsurface oxygen as well as the increase of density of under‐coordinated Cu sites, could enhance the production of multicarbon oxygenated species . This explanation, however, was recently refuted by Scott et al., who carried out electrochemical in‐situ grazing incidence X‐ray diffraction measurements to monitor the surface and composition changes of a Cu 2 O polycrystalline thin films under CO reductive conditions . They claimed that the oxide film was completely reduced to the metallic phase at potentials at which CO reduction activity was registered.…”

“…[69,82,[94][95][96] This explanation, however, was recently refuted by Scott et al, who carried out electrochemical in-situ grazing incidence X-ray diffraction measurements to monitor the surface and composition changes of a Cu 2 O polycrystalline thin films under CO reductive conditions. [97] They claimed that the oxide film was completely reduced to the metallic phase at potentials at which CO reduction activity was registered. Moreover, they observed faceting reconstruction in agreement with results from Kim et al.…”