la402496z_si_001.pdf (1.57 MB)
Electrogeneration of Single Nanobubbles at Sub-50-nm-Radius Platinum Nanodisk Electrodes
journal contribution
posted on 2013-09-03, 00:00 authored by Long Luo, Henry S. WhiteThe 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, inbp, 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 inbp 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.