Investigation on the dynamic behaviors of single surface CO nanobubbles during CO2 electroreduction in ionic liquids

CO nanobubbles generated on the electrode surface affects inevitably the reaction performance during the electroreduction of CO2. Understanding the dynamic behaviors of single surface CO nanobubbles, especially on the onset stage (i.e., nanobubble nucleation), has been received wide attentions in recent years. However, it is a great challenge to detect the nanobubble nucleation and evolution behaviors in-situ due to the transitory and nanoscale nature of nanobubble. In this work, for the first time, a single-entity electrochemistry method was developed to generate the single CO nanobubbles exclusively and stably in ionic liquids (ILs) by CO2 electroreduction. The unique dynamic behaviors of CO nanobubble and special regulations were revealed by the recorded voltammograms, where the critical supersaturation and the energy barrier for the CO nanobubble nucleation are much lower than that of other gases in aqueous solutions, thus CO nanobubbles are easy formed in ILs systems. It is proved through the classic nucleation theory that the main control factor of CO nanobubble nucleation is the relatively low surface free energy in ILs systems. Furthermore, experiments and simulations simultaneously revealed that the nanoelectrode surface is partially covered by the CO nanobubble due to the slower reaction kinetics instead of CO2 diffusion rate. The insights gained have relevant implications in regulating the behavior of nanobubbles as well as the performance of CO2 electroreduction to CO.