Nucleation and Analysis of Nanobubbles Observed by Single Entity Electrocatalysis in Microdroplets

ongoing

The NANOSEED, Nucleation and Analysis of Nanobubbles Observed by Single Entity Electrocatalysis in microDroplets, project seeks to directly electroanalyze microdroplet-confined nanobubble properties to elucidate the physical chemistry of their formation and reactivity. Its success will develop the first stochastic electrochemical method for nanobubble nucleation in microdroplet reactors, calculate important physical parameters of heterogenous nucleation processes under femtoliter confinement, and address the topical literature controversy regarding redox species generated and/or stabilized at gas|water interfaces. When a microdroplet collides with a microelectrode surface it forms a nanoscale contact area. By loading these microdroplets with acid, and applying a sufficient bias to the microelectrode, the hydrogen evolution reaction (HER) will occur at the microdroplet|microelectrode interface. Under conditions where the evolved hydrogen exceeds the critical concentration, a hydrogen nanobubble will nucleate in the microdroplet. The nanobubble is detected as a sharp decrease in cathodic current due to the insulating phase physically blocking molecular flux of the electrochemically active species (i.e., proton) to the microelectrode surface. Bulk mathematical models are re-derived for microdroplet reactors to relate the transient current-time profiles to nanobubble sizes and nucleation rates. Finite element simulations will validate the equations and provide additional information on the nanobubble geometry and nucleation site. The microdroplet is further used to confine radical oxygen species that may be produced at the nanobubble interface by accumulating the redox species to electrochemically-detectable levels. The detection of reactive oxygen species will provide clarity to an ongoing debate that may, in turn, reveal opportunities to leverage the harsh physical properties at the dielectric gas|water boundary to drive remarkable interfacial chemistry.