Effect of Nonuniform Mass Transport on Nanobubble Nucleation at Individual Pt Nanoparticles

Understanding nanoscopic bubble nucleation and growth is critical to reducing significant losses in efficiency during water electrolysis or photoelectrochemical hydrogen production. Herein, we demonstrate the controlled nucleation and growth of H₂ nanobubbles at individual Pt nanoparticles (NPs) via the hydrogen evolution reaction (HER) using the dual-barrel mode of scanning electrochemical cell microscopy (SECCM). The NPs, with an average radius of 35 nm, were dispersed on highly oriented pyrolytic graphite (HOPG), an otherwise inert surface, with a spacing much greater than the radius of the probe, allowing for the voltammetric recordings of HER at individual Pt NPs. Finite-element simulations indicate that the concentration of electrogenerated H₂ is highly nonuniform at the NP/solution interface, reaching a maximum at the three-phase HOPG/NP/solution boundary. Using finite-element modeling, we establish a correction factor to estimate the H₂ surface concentration required for nucleation, as determined from the maximum current measured just prior to bubble formation. Furthermore, a drop in ionic current is measured between the two barrels of the SECCM nanopipette upon bubble formation, in agreement with simulations of local conductance when a nanobubble blocks the current path.