Spontaneous Motion of Oil Droplets on Au Electrode during Sn Electrodeposition: Factors Creating Imbalance of Interfacial Tension

A nitrobenzene droplet put on an Au electrode moves spontaneously during Sn electrodeposition, which has been reported previously. The driving force of the motion is an imbalance of the interfacial tension of solid-water interface (γSW): the droplet moves when γSW acting on the front side of droplet is larger than that on the rear side. The electrodeposition, which increases γSW, is supressed by a side reaction such as hydrogen evolution reaction. Thus, if the electrode surface is non-uniform, the electrodeposition as well as the side reaction takes place non-uniformly on the electrode surface, resulting in the droplet motion. In other words, the non-uniform surface is one of the factors that create the interfacial tension imbalance. However, we have recently found that the droplet moves spontaneously on a uniform surface. This motion is initiated when nitrobenzene molecules are adsorbed non-uniformly on the surface, as discussed in this study.