If copper degradation required CO2 ER, one would expect the degradation kinetics to correlate with the electrochemical potential applied, which is contrary to what is observed . The enhanced degradation observed for larger copper particles is consistent with an increase in the local pH due to a parasitic hydrogen evolution reaction. Larger particles have more catalytic sites consuming hydrogen ions, which exacerbates the increase in local pH . Higher pH values favor the formation of a larger number of soluble Cu complexes, which contributes for accelerated corrosion in those microenvironment conditions (Figure ). Furthermore, the number of macro-and micro-defects -initiation corrosion sitescorrelates with particle size . Electrochemical plating is eclipsed by corrosion through formation of soluble copper-CO2-related complexes when a higher number of reactive sites is present. The enhanced corrosion of larger Cu particles and greater stability of small, re-plated particles observed in this study is contrary to thermodynamic stability theory predicting that larger particles are more stable and are expected to grow at the expense of small ones (Figure ) .