As a well‐known phenomenon, contact electrification (CE) has been studied for decades. Although recent studies have proven that CE between two solids is primarily due to electron transfer, the mechanism for CE between liquid and solid remains controversial. The CE process between different liquids and polytetrafluoroethylene (PTFE) film is systematically studied to clarify the electrification mechanism of the solid–liquid interface. The CE between deionized water and PTFE can produce a surface charges density in the scale of 1 nC cm−2, which is ten times higher than the calculation based on the pure ion‐transfer model. Hence, electron transfer is likely the dominating effect for this liquid–solid electrification process. Meanwhile, as ion concentration increases, the ion adsorption on the PTFE hinders electron transfer and results in the suppression of the transferred charge amount. Furthermore, there is an obvious charge transfer between oil and PTFE, which further confirms the presence of electron transfer between liquid and solid, simply because there are no ions in oil droplets. It is demonstrated that electron transfer plays the dominant role during CE between liquids and solids, which directly impacts the traditional understanding of the formation of an electric double layer (EDL) at a liquid–solid interface in physical chemistry.

of OER, a complex four-electron redox process involving OO bond formation that typically requires a high overpotential. [2] RuO 2 and IrO 2 are currently the stateof-the-art materials for OER, though the high cost and low earth abundance of Ru and Ir motivates the search for low-cost alternatives. Layered double hydroxides (LDHs), due to flexible chemical composition, show great potential in photo/ electrocatalysis. [3] Since the first report of NiFe-LDH-based materials exhibiting high OER activity, [4] much research effort has been directed toward the optimization of the OER activity of LDH materials. Hu and co-worker reported that monolayer NiM-LDH nanosheets (M = Fe, Co, etc.) exhibit efficient performance for water oxidation at low overpotentials (0.3 V at 10 mA m −2 ). [5] CoMn, [6] NiCo, [7] NiCoFe, [8] NiV, [9] and VFebased ultrathin LDH nanosheets also show good performance in OER, and core-shell Cu nanowires@NiFe-LDH nanosheets give excellent overall water splitting activity, [10] all the above mainly due to the high surface area and abundance of active surface sites. [11] However, the LDH nanosheet catalysts reported to date generally possess lateral platelet dimensions greater than 30 nm (Table S1, Supporting Information). These platelets are too large to dramatically improve the catalytic performance due to the limited availability of edge and corner sites that are typically highly reactive sites due to coordinative unsaturation. [12] Ultrafine monolayer LDHs with the lateral size of less than 3 nm containing highly exposed coordinatively unsaturated edge or corner active sites are thus a prized research target, potentially offering large catalytic performance improvements compared to conventional monolayer LDH nanosheets. However, the direct synthesis of ultrafine monolayer LDHs has proved extremely challenging to date, thus the potential of ultrafine monolayer LDHs to enhance catalytic and electrocatalytic applications remains unexplored.Traditionally, LDH nanosheets are synthesized with a lateral size of 30-200 nm and monolayer thicknesses using topdown (including solvent exfoliation [13] and plasma etching [14] ) or bottom-up approaches [5,15] (microemulsion methods [16] and layer growth inhibitors [15c,17] ). Reducing the lateral size further to sub-3 nm is challenging due to rapid crystallization kinetics and/or platelet aggregation. [18] Recently, 7.8 nm LDH nanoclusters containing only several layers were obtained using propylene oxide and acetylacetone as solvents, [19] and some ≈5 nm LDH nanosheets have been reported when LDHs were grown in situ on graphene-based supports. [20] Such approaches This study reports the synthesis of ultrafine NiFe-layered double hydroxide (NiFe-LDH) nanosheets, possessing a size range between 1.5 and 3.0 nm with a thickness of 0.6 nm. Abundant metal and oxygen vacancies impart the ultrafine nanosheets with semi-metallic character, and thus superior charge transfer properties and electrochemical water oxidation performance with overpotentials (η) of 254 mV r...

It has been demonstrated that substantial electric power can be produced by a liquid-based triboelectric nanogenerator (TENG). However, the mechanisms regarding the electrification between a liquid and a solid surface remain to be extensively investigated. Here, the working mechanism of a droplet-TENG was proposed based on the study of its dynamic saturation process. Moreover, the charge-transfer mechanism at the liquid−solid interface was verified as the hybrid effects of electron transfer and ion adsorption by a simple but valid method. Thus, we proposed a model for the charge distribution at the liquid−solid interface, named Wang's hybrid layer, which involves the electron transfer, the ionization reaction, and the van der Waals force. Our work not only proves that TENG is a probe for investigating charge transfer at interface of all phases, such as solid−solid and liquid−solid, but also may have great significance to water energy harvesting and may revolutionize the traditional understanding of the liquid−solid interface used in many fields such as electrochemistry, catalysis, colloidal science, and even cell biology.