Electrochemical Measurement of Hydrogen and Nitrogen Nanobubble Lifetimes at Pt Nanoelectrodes

Abstract

The lifetimes of individual H 2 and N 2 nanobubbles, electrochemically generated at Pt nanoelectrodes (7-85 nm-radius), have been measured using a fast-scan electrochemical technique. To measure lifetime, a stable single H 2 or N 2 bubble is first generated by reducing protons or oxidizing hydrazine, respectively, at the Pt nanoelectrode. The electrode potential is then rapidly stepped (<100 μs) to a value where the bubble is unstable and begins to dissolve by gas molecule transfer across the gas/water interface and diffusion. The electrode potential is immediately scanned back to values where the bubble was initially stable. Depending on the rate of this second voltammetric scan, the initial bubble may or may not have time to dissolve, as is readily determined by the characteristic voltammetric signature corresponding to the nucleation of a new bubble. The transition between these regimes is used to determine the bubble's lifetime. The results indicate that dissolution of a H 2 or N 2 nanobubble is, in part, limited by the transfer of molecules across the gas/water interface. A theoretical expression describing mixed diffusion/kinetic control is presented and fit to the experimental data to obtain an interfacial gas transfer rate of ∼10 Interfacial nanobubbles are gaseous, nanoscale spherical caps on a solid substrate immersed in a gas-saturated solution. They were first proposed to explain the long-range attractive interactions between hydrophobic surfaces.1-3 Initially their existence was contentiously debated, 4,5 but their existence, composition and stability has since been documented in numerous experiments. [6][7][8][9][10] The argument against their existence is due to the lack of a theoretical understanding of their peculiar longevity, often measured in days. 11It is well understood that a spherical bubble suspended in a gassaturated liquid should be intrinsically unstable. The internal pressure within a bubble of radius R exceeds that of its surroundings by the Laplace pressure, 2γ/R, where γ is the liquid's surface tension. The gas within the bubble therefore has a higher chemical potential than the dissolved gas and must reach equilibrium by dissolution into the liquid and transport away from the bubble. While this process is quite slow for macroscopic bubbles, the rate of dissolution increases by orders of magnitude for nanoscopic bubbles, due to the increase in Laplace pressure and decreased diffusion lengths. Epstein and Plesset 12 first detailed a theoretical framework for growing and shrinking bubbles and later Ljunggren and Eriksson 13 explicitly extended the theory to the nanoscale. Both mathematical approaches predict isolated, spherical bubbles smaller than 100 nm radius to dissolve in less than 100 microseconds. Experimentally, and as noted above, nanobubbles are observed to persist for much longer periods, often for several days. 11Several different mechanisms have been proposed to explain the persistence of nanobubbles on surfaces: a transport barrier and lowering of the surface tension b...

Interplay of the Open Circuit Potential-Relaxation and the Dissolution Behavior of a Single H2 Bubble Generated at a Pt Microelectrode

“…OCP decay measurements revealed a lifetime over a period of more than 100 s followed by dissolution of the adsorbed Pt-H intermediates. Formation and lifetime of a single nanobubble at a Pt nanoelectrode were also reported by Luo and White 12,13 . Opposite to Nakabayashi 11 a rapid dissolution of the nanobubble due to the high inner Laplace pressure is discussed, which is precisely balanced by the electrogeneration of H 2 at the partially exposed Pt surface, resulting in a dynamically stabilized nanobubble.…”

Surface nanobubbles: Theory, simulation, and experiment. A review

“…Moreover, the authors were able to observe the formation, growth, coalescence and eventual release of merged NBs from the HOPG substrate [143]. Electrochemical generation of individual H 2 , N 2 , and O 2 NBs have been reported as well in the literature [144][145][146][147][148][149][150][151]. In [148].…”

“…Electrochemical generation of individual H 2 , N 2 , and O 2 NBs have been reported as well in the literature [144][145][146][147][148][149][150][151]. In [148]. In particular, they found that the dissolution of NBs is partly limited by the translocation of molecules across the gas-water interface, where the interfacial gas transfer is estimated to be around 10 −9 mol/(N·s) [148].…”

Monitoring nanobubble nucleation at early‐stage within a sub‐9 nm solid‐state nanopore

“…The previous theoretical calculation predicted that bulk nanobubbles with a diameter of 10 nm tended to shrink and disappear due to the high inner pressure . Thus, the gas within the nanobubble inside the SiN X nanopore would dissolve into the solution, eventually . Moreover, after the nanobubble gradually occupying the limited volume of liquid‐liquid‐interface inside the nanopore, the encounter of two reaction liquids for H 2 production would be inhibited.…”

“…But this method is not sensitive enough for observing the nanobubble formation at its early‐stage. Recently, electrochemistry , transmission electron microscope and fluorescence microscopy have also been used for nanobubble studies. Among these methods, the electrochemistry method utilizes the confined electroactive surface of the nanoelectrode to directly produce and characterize nanobubbles .…”