Real‐time Monitoring Reveals Dissolution/Redeposition Mechanism in Copper Nanocatalysts during the Initial Stages of the CO₂ Reduction Reaction

Abstract

Size,m orphology,a nd surface sites of electrocatalysts have amajor impact on their performance.Understanding how, when, and why these parameters change under operating conditions is of importance for designing stable,a ctive,a nd selective catalysts.Herein, we study the reconstruction of aCubased nanocatalysts during the startup phase of the electrochemical CO 2 reduction reaction by combining results from electrochemical in situ transmission electron microscopyw ith operando X-ray absorption spectroscopy. We reveal that dissolution followed by redeposition, rather than coalescence, is the mechanism responsible for the sizei ncrease and morphology change of the electrocatalyst. Furthermore,w e point out the key role played by the formation of copper oxides in the process.U nderstanding of the underlying processes opens apathway to rational design of Cu electro (re)deposited catalysts and to stability improvement for catalysts fabricated by other methods.

Reconstruction of Copper Nanoparticles at Electrochemical CO2 Reduction Reaction Conditions Occurs via Two‐step Dissolution/Redeposition Mechanism

“…Since the nature of ex-situ study, starting Cu nanoparticles are in an oxidized form most likely due to exposure to the air, as well as the aqueous electrolyte. [11] Thus, we can safely consider the surface of NPs to be composed of Cu x O as a starting material prior to ERC. The same was also observed in other studies.…”

“…So far, copper-based catalysts have been observed to be highly susceptible for restructuring while exposed to the applied bias of the ERC. [7][8][9][10] Since nanostructured copper surfaces are prone to oxidation when exposed to the ambient air, water-based electrolyte immersion, [11] a local pH increase, [12] presence of undercoordinated atoms and grain boundaries [13] it is expected that copper oxide is present on the surface before ERC. [14,15] Oxide-derived copper (ODÀ Cu) catalysts are proposed to have high catalytic performance, however, the interpretation of this increase is still not settled.…”

“…Up to date, there have been different approaches to understand and reveal the process of the reconstruction and degradation mechanisms of nanostructured copper-based catalysts under ERC relevant conditions. [7][8][9]11,[15][16][17][18] Despite the multidisciplinary approaches that were employed to study Cu-based catalysts' reconstruction under ERC conditions, either through exsitu [7,16,18] and in-situ or operando [11,17,19,20] methods, there is still an active debate in the community regarding their actual mechanisms.…”

“…Recently, copper surface dis-solution was shown to be the main process that governs the reconstruction of nanostructured Cu-based catalysts. [11,12] Vavra et al [11] revealed dissolution/redeposition as the main degradation mechanism in the initial stages of ERC. Nevertheless, the insitu liquid TEM with all its limitations (e. g., beam-induced radiolysis effects) [23,24] provides only low-resolution morphological changes of the of Cu-based catalyst.…”

Sub‐Second Time‐Resolved Surface‐Enhanced Raman Spectroscopy Reveals Dynamic CO Intermediates during Electrochemical CO2 Reduction on Copper

“…[22] This additional peak is ascribed to redeposition of dissolved Cu 2+ /CuO x (OH) y species from solution, which were created during the anodic treatment. [22,23] Most of the redeposition process is complete after ca. 7s of reduction, which matches with the time scale of the observed transition of the adsorbed CO species from LFB-dominating to HFB-dominating (Figure 2b,c).…”