Fig. 1: Classification for the existing studies on liquid-solid CE based on the wettability of solid surfaces and charge polarity of water.
There are three types of solid surfaces, including polymer (FEP, etc.)18,22,51, self-assembled monolayer (PFOTS-SiO2, etc.)17,21,52,53,54, and inorganic solid that is chemically active in water (SiO2, etc.)20, which are distinguished by three different font colors. The solid surfaces are located in the position of their corresponding wettability. The positive and negative areas represent the polarity of water charges generated during liquid-solid CE. The sign “?” means the area yet to be explored, i.e., whether the water can acquire the negative charges from the superhydrophobic surfaces. Note that some works report mutually conflicting results regarding the charge polarity or the surface wettability. For example, SiO2 is reported as hydrophobic in literature21 (marked bya), and water is positively charged by PP in literature51 (marked byb).
