Raindrops are an abundant micromechanical renewable energy source in nature, and raindrop energy harvesting has always been a research hotspot. Traditional hydropower generation is not suitable for low-frequency energy harvesting, and it is difficult to realize distributed energy harvesting. The development of triboelectric nanogenerator (TENG) is a promising strategy for converting raindrop energy in the environment into electrical energy. Polydimethylsiloxane (PDMS) composite has received much attention due to its excellent chemical stability and insulating properties for TENG. However, the deficiency of the low output performance and insufficient hydrophobicity of PDMS limits the application of PDMS in droplet energy capture. Modification of PDMS can improve the droplet energy collection capability of the liquid–solid contact triboelectric (LS-TENG). In this work, a new approach to modifying polydimethylsiloxane (PDMS) as a hydrophobic negative triboelectric material using a high dielectric constant MXene and a hydrophobic nano-SiO2 was reported. The as-prepared composites′ permittivity and triboelectric performance were remarkably promoted as compared to composites without interfacial modification. In addition, the use of composites for TENG assembly improved the open-circuit voltage and short-circuit current by a factor of 47.5 and 25.21, respectively, compared to pure PDMS. Application of the composite to the assembled TENG was employed as energy harvester to light up LEDs and charge a capacitor. In addition, a cathodic protection system was designed to demonstrate its potential application in the field of electrochemistry. This provides guidance for the practical implementation of TENGs in the field of electrochemical cathodic protection.