Cu+ transient species mediate Cu catalyst reconstruction during CO2 electroreduction

Abstract

Understanding metal surface reconstruction during operation is of the uttermost importance in heterogeneous catalysis as it directly affects the available active sites. However, surface reconstruction is notoriously difficult to study because of the dynamic nature of the phenomena behind it. Here, we report on the mechanism and the intermediates, which drive the rearrangement of copper catalysts during the electrochemical CO2 reduction reaction. In-situ methods, including mass spectrometry and fluorescence spectroscopy, evidence a dissolution – redeposition process mediated by transient species containing copper in +1 oxidation state. Theory identifies copper-adsorbate complexes which form in solution under operating conditions. Copper carbonyls and oxalates emerge as the major reaction-specific species driving copper reconstruction. This work motivates future studies to specifically target these compounds to improve the catalyst operational stability in the electrochemical CO2 reduction reaction.

Probing the Dynamics of Low-Overpotential CO2-to-CO Activation on Copper Electrodes with Time-Resolved Raman Spectroscopy

“…This hypothesis is in line with the high-intensity signals we observed in the carbonate and CO Raman regions as well as the boosted activity for CO at low overpotentials (see Figure S21). Furthermore, copper carbonate transient species were elucidated through in situ fluorescence spectroscopy, and the authors invoked these transient copper carbonate complexes as highly active phases for CO formation in a dissolution–redeposition mechanism, in line with our findings . We therefore ascribe the low-overpotential CO 2 -to-CO activation observed in our combined PE and TR-SERS experiments to an alternative reaction pathway that involves malachite copper carbonate hydroxide complexes in the electrolyte solution, which generates a highly active site upon redeposition and subsequent reduction.…”

Structural Transformation and Degradation of Cu Nanocatalysts during Electrochemical CO2 Reduction Reaction

“…However, a study suggests that surface-bound CO 2 RR intermediates (e.g., *CO and *C 2 O 4 ) can enhance the dissolution of Cu surface atoms, which would be minimized under N 2 conditions. 33 A similar observation of CO 2 RR intermediates enhancing the degradation of the catalyst surface has been reported on Au NPs. 7 These previous ndings suggest that Cu dissolution is not a major factor in the enhanced declustering observed under Ar conditions.…”

How Temperature Affects the Selectivity of the Electrochemical CO2 Reduction on Copper

“…Recently, the group of Buonsanti , showed that Cu dissolves under negative applied potentials, with subsequent redeposition on the electrode roughening the electrocatalyst surface. Based on their results, we hypothesize that this dissolution can be promoted by small amounts of oxygen in the system as they show that the dissolution is enhanced in air . Even though CO 2 is being purged throughout the experiment, we cannot guarantee that the cell is completely oxygen-free.…”

“…Based on their results, we hypothesize that this dissolution can be promoted by small amounts of oxygen in the system as they show that the dissolution is enhanced in air. 62 Even though CO 2 is being purged throughout the experiment, we cannot guarantee that the cell is completely oxygen-free. At higher temperatures, surface diffusion of the copper atoms is expected to be enhanced.…”