Understanding metal surface reconstruction is of the uttermost importance in heterogeneous catalysis as this phenomenon directly affects the nature of available active sites. However, surface reconstruction is notoriously difficult to study because of the dynamic nature of the phenomena behind it, particularly when solid/liquid interfaces are involved. Here, we report on the intermediates which drive the rearrangement of copper catalysts for the electrochemical CO2 reduction reaction (CO2RR). Online mass spectrometry and UV-Vis absorption spectroscopy data are consistent with a dissolution–redeposition process, previously demonstrated by in-situ electron microscopy. The data indicate that the soluble transient species contain copper in +1 oxidation state. Density functional theory identifies copper adsorbate complexes which can exist in solution under operating conditions. Copper carbonyls and oxalates are suggested as the major reaction-specific species driving copper reconstruction during CO2RR. This work motivates future methodological studies to enable the direct detection of these compounds and strategies which specifically target them to improve the catalyst operational stability.