The liquid-solid (L-S) interface, ubiquitous in nature, serves as a critical boundary for addressing fundamental scientific problems. Its prevalence and intricate dynamics underpin a wide range of essential physical and chemical phenomena essential to fields such as catalysis, energy, sensors and environmental science, offering profound opportunities for exploration in various disciplines. The functionality of the L-S interface is rooted in charge accumulation and release driven by potential gradients or disparities in material properties across the phases. This chapter delves into the mechanisms of contact electrification (CE) at L-S interfaces, emphasizing charge transfer processes across interfaces involving conductors, dielectrics, and semiconductors. It emphasizes the formation and dynamics of the electrical double layer (EDL), a fundamental structure regulating charge behavior at interfaces. Wang's two-step model is introduced to elucidate the role of CE in EDL formation on dielectric surfaces. Key discussions include ion and electron transfer quantification, advanced electron transfer modeling, and the hybrid characteristics of the EDL, shedding light on the physics of L-S CE. The chapter explores techniques for dynamic EDL regulation through electric fields or mechanical methods to control charge carrier behavior. By modulating ion migration and optimizing charge concentration at interfaces, these strategies directly influence energy scavenging, storage, and processes of information flow etc. Practical applications of L-S CE are demonstrated across various devices. At liquid-conductor interfaces, EDL regulation underpins efficient energy storage in supercapacitors and the functionality of electrochemical sensors. For liquid-dielectric interfaces, the dynamic regulation of the EDL has catalyzed innovations in high-efficiency energy harvesting and information flow, such as triboelectric nanogenerators (TENGs) and triboiontronic nanogenerators (TINGs). At liquid-semiconductor interfaces, the tribovoltaic effect harnesses L-S CE for effective direct current (DC) energy generation. These advancements highlight the vast and new application potential of EDL regulation at L-S interfaces, laying the foundation for breakthroughs in energy and information technologies.