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

Single H-2 nanobubble nucleation is studied at Pt nanodisk electrodes of radii less than 50 nm, where H-2 is produced through electrochemical reduction of protons in a strong acid solution. The critical concentration of dissolved H-2 required for nanobubble nucleation is measured to be similar to 0.25 M. This value is similar to 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 H-2 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 H-2 nanobubble nucleation. Furthermore, amphiphilic surfactant molecules accumulate at the H-2/solution interface, hindering interfacial H-2 transfer from the nanobubble into the solution; consequently, the residual current decreases with increasing surfactant concentration.