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

Abstract

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.

Single-Entity Electrochemistry of Nano- and Microbubbles in Electrolytic Gas Evolution

“…Later, the Ren group employed a ∼500 nm radius dual-barrel pipet and performed a delicate electrochemical imaging of electrolytic gas bubble nucleation across the polycrystalline Pt film (Figure a) . Although an abrupt current reduction attributed to bubble formation was justified, the formed nanobubble exhibited poor stability with large discrepancy between voltammetric responses, which was reconfirmed by the White group using a similar dual-barrel configuration SECCM . We speculate the fast gas-exchange at the liquid–air interface at the nanoscopic droplet quickly dissipates the local gas supersaturation.…”

“…81 Although an abrupt current reduction attributed to bubble formation was justified, the formed nanobubble exhibited poor stability with large discrepancy between voltammetric responses, which was reconfirmed by the White group using a similar dual-barrel configuration SECCM. 82 We speculate the fast gas-exchange at the liquid−air interface at the nanoscopic droplet quickly dissipates the local gas supersaturation. Our group carried out a modified electrochemical study of bubble nucleation using a single-barrel micropipette.…”

The new era of high throughput nanoelectrochemistry

“…If the substrate is a conductor, it is usually connected as the working electrode (WE) and an additional voltage, applied between the QRCEs and the WE, facilitates the implementation of a variety of electrochemical techniques, within the confines of the miniature cell. Voltammetry experiments [207][208][209][210][211][212][213][214][215][216][217][218] and chronoamperometry experiments 207,219 are used to investigate the local electrochemical activity and to induce and monitor phase changes (Figure 5C). At the same time, the ionic current informs of any change occurring in the meniscus, e.g., the nucleation and growth of gas bubbles.…”

“…At the same time, the ionic current informs of any change occurring in the meniscus, e.g., the nucleation and growth of gas bubbles. 212 With vertical tip position modulation SECCM, the surface topography can be tracked in a constant-distance mode (Figure 5B), where the probe does not break contact with the substrate. 205 In this case, the potential versus the surface is kept stable, or swept while lateral movement is briefly interrupted.…”

“…Individual Pt NPs on HOPG were encapsulated by a double-barrel pipette meniscus and H + reduction was performed. 212 In this case, the pipette configuration allowed monitoring of bubble evolution via the ionic current flowing between the two barrels. Aided by FEM simulations, the relationship between the measured current peak and the local gas concentration was clarified.…”