Revealing the Active Phase of Copper during the Electroreduction of CO₂ in Aqueous Electrolyte by Correlating In Situ X-ray Spectroscopy and In Situ Electron Microscopy

Abstract

The variation in the morphology and electronic structure of copper during the electroreduction of CO2 into valuable hydrocarbons and alcohols was revealed by combining in situ surface- and bulk-sensitive X-ray spectroscopies with electrochemical scanning electron microscopy. These experiments proved that the electrified interface surface and near-surface are dominated by reduced copper. The selectivity to the formation of the key C–C bond is enhanced at higher cathodic potentials as a consequence of increased copper metallicity. In addition, the reduction of the copper oxide electrode and oxygen loss in the lattice reconstructs the electrode to yield a rougher surface with more uncoordinated sites, which controls the dissociation barrier of water and CO2. Thus, according to these results, copper oxide species can only be stabilized kinetically under CO2 reduction reaction conditions.

On the Activity/Selectivity and Phase Stability of Thermally Grown Copper Oxides during the Electrocatalytic Reduction of CO2

“…These changes in the morphology were also recently observed under reaction conditions in situ using an electrochemical scanning electron microscope with electrodeposited copper oxide electrodes indicating a reconstruction in the electrode because of the oxygen loss during the CO 2 RR. 38 However, Figure 2 D2 shows that the electrode oxidized at 300 °C (Cu(II) oxide) underwent partial dissolution because of the electrical current flowing along a narrow path and Joule heating inducing cathodic breakdown, or as a consequence of the erosion induced during the copper oxide phase changes yielding a spongy porous morphology composed of electrically isolated patches/islands (see also Figure S2 ). A magnification of these electrodes before and after the CO 2 RR is shown in Figure S3 in the Supporting Information .…”

Graphene-Capped Liquid Thin Films for Electrochemical Operando X-ray Spectroscopy and Scanning Electron Microscopy

“…At the same time, graphene provides electrical conductivity 19 , 20 and is mostly transparent to a wide range of wavelengths 21 − 23 and slow electrons. 24 − 26 These benefits allow studies under wet conditions using surface sensitive spectroscopy 27 − 29 or electron microscopy with the same type of sample.…”

Potentialabhängige Morphologie von Kupferkatalysatoren während der Elektroreduktion von CO2, ermittelt durch In‐situ‐Rasterkraftmikroskopie

“…This is in line with the assumption that the surface is mainly composed of metallic copper under such reducing conditions. [21] Direct insight into effects of CO2 and CO2RR products onto surface morphology can be found in data recorded in CO2-free Ar-saturated electrolyte ( Figure S7). Images evidence a reduced electrochemical annealing effect at -0.5 VRHE.…”

“…In situ AFM can provide high-resolution information on the nature of the defects and prevalence under a given electrochemical potential, with advantages in identification and surface sensitivity over ATR-FTIR and electron microscopy. [21] To this end, we compared step edge density estimates for copper surfaces during CO2RR at different reducing potentials with those for as-prepared samples and found variations in line defect densities as a function of the sample state (Figure 4e). Asprepared electropolished Cu(100) electrodes exhibit the lowest defect densities.…”

“…Progress has been made in the understanding of CO2RR by combining for instance bulksensitive X-ray absorption spectroscopy with in situ electrochemical scanning electron microscopy (SEM). [21] Yet, alternative local-imaging methods must be sought, such as scanning probe microscopy, in order to study catalyst surfaces in situ with local spatial resolution down to the atomic scale. Scanning tunneling microscopy (STM) has provided key insights into the surface chemistry and corrosion of copper.…”