Recent progress in blue energy harvesting for powering distributed sensors in ocean

Oceanography has received a lot of attention in the 21st century. Due to the harsh and complex ocean conditions, ensuring power supply to the distributed marine equipment has become a critical challenge. The ocean kinetic energy harvester (OKEH) has made favorable progress in powering ocean sensors by harvesting blue energy. The latest developments in the electromagnetic harvester (EMH), electroactive polymers harvester (EAH), triboelectric nanogenerator (TENG), and hybrid harvester (HH) are reviewed in this study. This study analyzes the working principles and output performance of the OKEH as well as highlights the future challenges of and perspectives on the OKEH. Based on the comparison of OKEHs, this study indicates that TENG is favorable for harvesting low-frequency, low-amplitude, and random-direction wave energy (called high entropy energy).