The structure of Cu nanocrystals as catalysts for the electrochemical reduction of CO2 is a subject of considerable contemporary interest. Recent efforts have focused mainly on the preparation of Cu nanocrystals, but the question of their stability is equally relevant and has not been considered as extensively. Herein, we report on the reconstruction of Cu nanocrystals during CO2 reduction and discuss the factors influencing the observed changes with computerbased quantitative analysis and spectroscopic techniques. The timelines of opposing phenomena, sintering and declustering, previously reported separately, are detailed with a focus on two forces affecting the final morphology: applied potential and reaction intermediates. This intriguing system demonstrates the need for fundamental understanding of catalyst behavior preceding the ability to control its performance.