Enhanced Reduction of CO₂ to CO over Cu–In Electrocatalysts: Catalyst Evolution Is the Key

Copper–indium catalysts have recently shown promising performance for the selective electrochemical reduction of CO₂ to CO. In this work, we prepared Cu–In nanoalloys by the in situ reduction of CuInO₂ and In₂O₃-supported Cu nanoparticles and found that the structure of these nanoalloys evolves substantially over several electrocatalytic cycles, in parallel with an increase in the activity and selectivity for CO evolution. By combining electrochemical measurements with ex situ characterization techniques, such as XRD, STEM, elemental mapping, and XPS, we show that this behavior is caused by the segregation of copper and indium in these materials, resulting in the formation of a heterogeneous nanostructure of Cu-rich cores embedded within an In­(OH)₃ shell-like matrix. The evolved catalysts show high electrocatalytic performance at moderate overpotential (i.e., j_CO > 1.5 mA cm^–2 at −0.6 V vs RHE). We found that the removal of In­(OH)₃ from these heterogeneous nanostructures decreases the performance of the evolved catalysts, particularly in terms of the selectivity toward CO, which then recovers with the reappearance of the hydroxide following the re-equilibration of the material. On the other hand, an In­(OH)₃-supported Cu catalyst exhibits a current efficiency for CO comparable to that of the evolved nanoalloys without the need for an equilibration stage, indicating that In­(OH)₃ plays a crucial role in favoring the production of CO over Cu–In electrocatalysts. These findings shed light on the link between the architecture of these materials and their performance and underscore the potential of nonreducible hydroxides to act as promoters in CO₂ reduction electrocatalysis.