Electron transfer in liquid–solid contact electrification and double-layer formation

The liquid–solid (L-S) interface is one of the most important surface sciences subject in chemistry, catalysis, energy provision and even biology. The formation of an electric double-layer (EDL) at the L-S interface is thought to be due to the adsorption of a layer of ions on the solid surface, resulting in the redistribution of ions in the liquid. Although the existence of a layer of charge on a solid surface has always been assumed, the source of the charge has not been widely explored. Recent studies of contact electrochemistry (CE) between liquids and solids have shown that electron transfer plays a dominant role in the initial stage of charge layer formation at the L-S interface. Here, we review recent studies on electron transfer in liquid–solid CE, including liquid-insulator, liquid-semiconductor, and liquid-metal scenarios. Considering the existence of electron transfer on the L-S interface, we reconsider the formation of EDL. In addition, a liquid–solid CE based triboelectric nanogenerator (TENG) technique is introduced, which can be used not only to obtain mechanical energy from liquid, but also as a probe to detect charge transfer at liquid–solid interface.