Electrochemical Measurements of Single H₂ Nanobubble Nucleation and Stability at Pt Nanoelectrodes

Abstract

Single H₂ nanobubble nucleation is studied at Pt nanodisk electrodes of radii less than 50 nm, where H₂ is produced through electrochemical reduction of protons in a strong acid solution. The critical concentration of dissolved H₂ required for nanobubble nucleation is measured to be ∼0.25 M. This value is ∼310 times larger than the saturation concentration at room temperature and pressure and was found to be independent of acid type (e.g., H₂SO₄, HCl, and H₃PO₄) and nanoelectrode size. The effects of different surfactants on H₂ nanobubble nucleation are consistent with the classic nucleation theory. As the surfactant concentration in H₂SO₄ solution increases, the solution surface tension decreases, resulting in a lower nucleation energy barrier and consequently a lower supersaturation concentration required for H₂ nanobubble nucleation. Furthermore, amphiphilic surfactant molecules accumulate at the H₂/solution interface, hindering interfacial H₂ transfer from the nanobubble into the solution; consequently, the residual current decreases with increasing surfactant concentration