Ocean waves, the most widely distributed energy source within the marine environment, promise renewable energy for next-generation self-sufficient ocean exploration and monitoring instrumentation. Triboelectric nanogenerator (TENG) technology has shown the potential in harvesting ocean wave energy. However, most TENG designs suffer from challenges such as relatively low contact intimacy and energy power density, limiting their practical application. This paper proposes a solid–liquid-interfaced, tube-shaped triboelectric–electromagnetic hybrid nanogenerator (TTEHG) to efficiently capture wave energy. Owing to the solid–liquid interface in conjunction with the coupled TENG and the electromagnetic generator (EMG) design, the TTEHG features a reduced frictional loss and broadened range of harvestable wave energy. At a frequency of 1 Hz, the instantaneous power density and current density of the TTEHG are 0.25 mW·cm–3 and 5 mA·cm–3, respectively. Even at an ultra-low operational frequency of 0.2 Hz, the TTEHG exhibits an excellent output performance with a peak current of nearly 15 mA, and is able to power various functional electronic devices, such as temperature and humidity sensors, to monitor the marine environment. The TTEHG was deployed in Sanya Bay, China, to demonstrate its practical application in harsh ocean environments.