The vast energy stored in the ocean, which receives an average solar power of ≈60 000 TW per year, surpasses human energy consumption by three orders of magnitude. Harnessing even a small fraction of it holds great promise in addressing global energy and water crises. Here, an integrated device that achieves unprecedented power density up to 1.1 W m−2 with excellent stability through a salinity concentration gradient induced by solar evaporation, while simultaneously producing clean water at a rate of 1.25 kg m−2 h−1 under one sun irradiation is presented. The remarkable electricity generation capability stems from the unique interlayer structure of polyaniline-graphene oxide-MnO2 (PANI@GO/MnO2) electrodes, enabling the recovery of electrochemical potentials from a wide range of ion salinity concentrations within the device and the additional Donnan potential generated by the anion-exchange membrane. Furthermore, periodic flipping of the device effectively reactivates the electrodes and suppresses salt accumulation, enabling long-term operation. Notably, a prototype device of 8 × 25 cm2 exhibits a short-circuit current of 10 mA and an open-circuit voltage of 10.2 V, as well as a clean water production rate of 24.8 g per hour. These findings shed light on the reliable technology for power and freshwater supply in marine environments.