Electrogeneration of Single Nanobubbles at Sub-50-nm-Radius Platinum Nanodisk Electrodes

The electrochemical generation of individual H₂ nanobubbles at Pt nanodisk electrodes immersed in a 0.5 M H₂SO₄ solution is reported. A sudden drop in current associated with the transport-limited reduction of protons is observed in the i–V response at Pt nanodisk electrodes with radii of less than 50 nm. This decrease in current (∼95% blockage) corresponds to the formation of a single H₂ nanobubble attached to the nanoelectrode that blocks proton transport to the surface. The current at which nanobubble formation occurs, i_nb^p, is independent of scan rate and H₂SO₄ concentration (for [H₂SO₄] > 0.1 M), indicating a critical concentration profile of electrogenerated H₂ required to nucleate a nanobubble. Finite element simulation based on Fick’s first law, combined with the Young–Laplace equation and Henry’s law, indicates that the concentration of H₂ near the nanoelectrode surface at i_nb^p exceeds the saturation concentration necessary to generate a nanobubble with a size comparable to the electrode size. The rapid dissolution of the nanobubble due to the high inner Laplace pressure is precisely balanced by the electrogeneration of H₂ at the partially exposed Pt surface, resulting in a dynamically stabilized nanobubble. Preliminary measurements of the i–t response during nanobubble formation indicate a two-step nucleation and growth mechanism with time scales on the order of 100 μs (or less) and ∼1 ms, respectively.