The use of triboelectrification to collect dissipated energy in the environment to realize the in-situ cathodic protection of metal materials is a new clean, economical, and environmentally friendly strategy. However, the low output current density of triboelectric nanogenerators (TENGs) based on the normal inclined surface structure (I-TENG) greatly limits their application in the field of metal material cathodic protection owing to their impressed current cathodic protection capability. Here, we designed a new droplet TENG based on an arc-shaped surface structure (A-TENG) and organic coating materials to increase the output current density by more than an order of magnitude. With this new type of A-TENG, the water droplets can move on the arc-shaped structure to increase their contact-separation speed and effective contact-separation area with the triboelectric resin surface, thereby generating more triboelectric charges. The new structure can also prevent the droplets from splashing during the collision of the interface, which leads to the reduction of the triboelectric performance. Compared with I-TENG, the short-circuit current of A-TENG increases from 0.6 μA to18 μA, with an output voltage of 80 V and a power of up to 322 μW, which can easily light 50 commercial LEDs with one water droplet. In addition to the high-efficiency collection of energy from water droplets, it can also be designed as an efficient self-powered cathodic protection device for metals against corrosion through spraying on a large area. Under the action of A-TENG, the corrosion potential of the A3 carbon steel electrode dropped significantly by 580 mV, with an obvious increase in corrosion current density because the negative friction charges from TENG transferred to the surface of the protected metals for efficient impressed current cathodic protection. This device has the advantages of simple structure, low price, large-scale realization, and great application potential in ocean energy harvesting, sensing, and the self-powered corrosion protection of various marine equipment.