High‐Speed AFM Observation of Electrolytic Hydrogen Nanobubbles During Potential Scanning

Abstract

ABSTRACTNano‐sized bubbles (NBs: nanobubbles) have attracted attention in various fields such as physics, engineering, medicine and agriculture for fundamental and practical reasons. Atomic force microscopy (AFM) has revealed the occurrence of NBs and discovered their flattened shape. However, their dynamic behaviours have not yet been discussed much owing to the slow scanning speed. The existence of these energetically unfavourable structures is still controversial owing to the lack of studies on bubble‐like behaviour of NB such as aggregation, growth and dissolution. Recently developed high‐speed AFM (HS‐AFM) can observe nano‐interface phenomena at a speed of 0.5 frame s−1. In this study, HS‐AFM was applied to electrolytic H2 NBs. We successfully observed NB nucleation, growth and dissolution during a potential scan. Image analysis revealed flattened nuclei with heights of less than 10 nm. The NBs remained stable for a short period after the hydrogen evolution stopped, and they rapidly dissolved at the anodic potential. As the potential sweep was repeated, the number of NB nuclei increased. This is the first study showing the dynamic motion of NBs during the potential sweep by AFM. Videos captured by HS‐AFM make NB existence more certain. This research contributes not only to the NB study but also to the clarification of the gas evolution mechanism on electrodes.