High-Speed AFM Observation of Electrolytic Nanobubbles Formation on HOPG

Abstract

IntroductionNanobubbles (NBs) on solid surfaces are an interesting topic for surface and colloid science. Since the diameter of NBs is less than 1 μm, NBs can be morphologically measured by atomic force microscope (AFM) [1]. However, due to the slow scanning speed of conventional atomic force microscope (AFM), the nucleation and growth process is not yet known. We previously applied high-speed AFM (HS-AFM) for NBs’ evolution during water electrolysis [2]. Here, we discuss the NBs’ formation during cyclic voltammetry (CV).ExperimentalThe experimental cell was a three-electrode system at room temperature. The working electrode was highly ordered pyrolytic graphite (HOPG). The counter and reference electrodes were Pt wires. The electrolyte was a sulfuric acid solution (5 mmol L-1). CV was performed by a potentiostat. HS-AFM was operated in dynamic mode. The scanning speed was 0.5 frame s-1 and the size was 1 × 0.75 µm2.Results and discussionWhen the potential was swept to the anode from the open circuit potential, the pancake-like NBs were formed (Fig. 1). The height was ~5 nm, and the surface roughness was very small (< 1 nm). The pancake NBs grew along the step side and moved actively on the surface. They occasionally coalesced with neighboring NBs.On the other hand, when the potential was swept to the cathode, the dynamic process was the opposite. The pancake NBs dissolved. This poster will present the dynamic variation of electrolytic NBs during the CV.Reference[1] X.H. Zhang et al., Langmuir, 23, 1778 (2007).[2] M Mita, H Matsushima, M Ueda, H Ito, J. Colloid Interface Sci., 641, 389 (2022). Figure 1