The study investigates the structural evolution of Cu nanocubes during the electrochemical reduction of CO₂, a process known but poorly understood. Using a combination of techniques including identical location transmission electron microscopy (IL-TEM), cyclic voltammetry (CV), in situ X-ray absorption fine structure spectroscopy (XAFS), and ab initio molecular dynamics simulation, the researchers found that Cu catalysts undergo a previously unexplored pathway of reconstruction—alkali cation-induced cathodic corrosion—when the electrode potential is more negative than an onset value (e.g., −0.4 V\_OHE in 0.1 M KHCO₃). The presence of alkali cations in the electrolyte is critical for this process, leading to dynamic morphologies of Cu catalysts. While these reconstructions do not necessarily prevent stable electrocatalytic reactions, they limit long-term selectivity and activity enhancement by controlling the morphology of Cu pre-catalysts. Operating Cu catalysts at less negative potentials (e.g., −0.37 V\_RHE) in the CO electrochemical reduction (CORR) can mitigate cathodic corrosion, allowing Cu nanocubes to maintain a stable selectivity advantage over spherical Cu nanoparticles. The findings highlight the importance of understanding and managing alkali cation-induced cathodic corrosion to optimize the performance of Cu catalysts in CO₂ reduction reactions.The study investigates the structural evolution of Cu nanocubes during the electrochemical reduction of CO₂, a process known but poorly understood. Using a combination of techniques including identical location transmission electron microscopy (IL-TEM), cyclic voltammetry (CV), in situ X-ray absorption fine structure spectroscopy (XAFS), and ab initio molecular dynamics simulation, the researchers found that Cu catalysts undergo a previously unexplored pathway of reconstruction—alkali cation-induced cathodic corrosion—when the electrode potential is more negative than an onset value (e.g., −0.4 V\_OHE in 0.1 M KHCO₃). The presence of alkali cations in the electrolyte is critical for this process, leading to dynamic morphologies of Cu catalysts. While these reconstructions do not necessarily prevent stable electrocatalytic reactions, they limit long-term selectivity and activity enhancement by controlling the morphology of Cu pre-catalysts. Operating Cu catalysts at less negative potentials (e.g., −0.37 V\_RHE) in the CO electrochemical reduction (CORR) can mitigate cathodic corrosion, allowing Cu nanocubes to maintain a stable selectivity advantage over spherical Cu nanoparticles. The findings highlight the importance of understanding and managing alkali cation-induced cathodic corrosion to optimize the performance of Cu catalysts in CO₂ reduction reactions.