| Abstract: | Harvesting energy directly in oceans by electrochemical devices is essential for driving underwater appliances such as underwater vehicles or detectors. Owing to the extreme undersea environment, it is important but difficult to use the devices with both a high energy density and power density simultaneously. Inspired by marine organisms that have switchable energy extraction modes (aerobic respiration for long‐term living or anaerobic respiration to provide instantaneously high output power for fast movement), an auto‐switchable dual‐mode seawater energy extraction system is presented to provide high energy density and power density both by initiatively choosing different solutes in seawater as electron acceptors. With assistance from metal–organic frameworks, this device had a theoretical energy density of 3960 Wh kg?1, and a high practical power density of 100±4 mW cm?2 with exceptional stability and low cost, making practical applications in seawater to be possible. |
