Electrochemical CO2 conversion into valuable chemicals and fuels offers a promising route to reduce greenhouse gas emissions and close the carbon cycle. Copper nanocube (NC) catalysts with well-defined (100) facets are particularly attractive for their selective ethylene production. However, scaling up CO2 electroreduction (CO2ER) is hindered by rapid catalyst deactivation due to structural degradation and loss of active sites. Understanding catalyst restructuring under operational conditions is crucial for designing stable, efficient CO2ER systems. This thesis presents a fundamental study of the restructuring pathways of Cu NCs catalysts during CO2ER, using electrochemical liquid-phase electron microscopy (ec-LPEM). First, a statistically relevant population of Cu NCs was monitored via energy-filtered liquid-phase transmission electron microscopy (LPTEM) during CO2ER. The results revealed that restructuring occurs through concurrent pathways of dissolution, redeposition, reattachment as well as fragmentation. This effectively leads to a decrease in the fraction of the selective (100) facets, which presumably results in catalyst deactivation. Furthermore, a series of surface oxidized Cu and Cu2O NCs were studied using LPTEM and the results were compared to their catalytic performance. The analysis revealed that oxide-rich NCs are more susceptible to restructuring and deactivation, with Cu carbonate formation identified as a key contributor to these processes. These studies were made possible through imaging under energy-filtered conditions and signal detection by direct electron devices, providing improved image contrast in liquid and enhanced temporal resolution. Meanwhile, stable LPTEM monitoring of the catalysts under cathodic potential was achieved by optimizing conventionally used glassy carbon (GC) electrodes as supports for the Cu NCs. Finally, to facilitate future high-resolution imaging of catalysts, essential for the in-depth understanding of catalyst (de)activation, graphene (Gr) was integrated as the membrane and electrode material into the electrochemical microchip. The results revealed that, in addition to improved spatial resolution, Gr possesses a wider inert potential range than conventional GC electrodes, enabling more realistic cathodic potentials. Real-time LPSEM imaging of Cu NCs with Gr microcells showed similar restructuring via dissolution/redeposition, as was previously reported with LPTEM. This confirms that integration of Gr electrodes in the microchips can advance the field.