Extraction of Salinity‐Gradient Energy by a Hybrid Capacitive‐Mixing System

Salinity‐gradient energy (SGE) is a renewable energy source available wherever two solutions with different salinity mix. Capacitive‐mixing (Capmix) is a technology that directly extracts the SG potential through the movements of ions in high‐ and low‐concentration solutions. However, the energy‐harvesting performance of Capmix needs further improvement. Herein, a hybrid Capmix that consists of a battery and capacitive electrodes is proposed. In this system, sodium ions and anions are captured/released by the metal oxide and carbon electrodes, respectively. The hybrid Capmix extracted an energy density that was approximately three times higher (130 J m−2) and exhibited a notable power output (97 mW m−2) compared to the previous Capmix using ion‐exchange membranes. Furthermore, the hybrid system operated successfully with real river water and seawater. These results suggest that the hybrid Capmix could be a viable option to harvest energy from salinity gradients. Synergistic effect! A hybrid capacitive‐mixing system that consists of a battery and capacitive electrodes with an anion‐exchange membrane was fabricated to harvest salinity‐gradient energy. From the developed voltage rise induced by the concentration difference of sea water and river water, the hybrid system could capture energy of up to 130 J m−2 with significant power output.