A charge-free and membrane-free hybrid capacitive mixing system for salinity gradient energy harvesting

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2023-02, Vol.11 (7), p.3388-3398
• Main Authors: Yang, Bin, Yu, Jian, Ma, Tianwei
• Format: Article
• Language: English
• Subjects: Activated carbon; Electric power generation; Electrolytes; Energy; Energy harvesting; Ethylenediamine; Hybrid systems; Ion exchange; Ions; Membranes; Pigments; Power management; Power sources; Salinity; Salinity effects; Sodium chloride
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d2ta08213f

Capacitive mixing (CapMix) is a promising technology to harvest salinity gradient energy (SGE) by generating electricity through the potential difference owing to electrolyte salinity change at the electrode/electrolyte interface. However, existing CapMix methods suffer from the high cost of ion-exchange membranes, additional energy investment, and limited energy density and cycle life. Herein, we propose a charge-free and membrane-free hybrid CapMix system consisting of ethylenediamine-modified activated carbon (EDA-YP80F) as a capacitive anode and a Prussian blue analog, iron hexacyanoferrate (FeHCF), as a battery-type cathode. The selective incorporation/absorption of Na + ions and Cl − ions into FeHCF and EDA-YP80F achieves a membrane-free operation. The matching potentials of FeHCF and EDA-YP80F enable reversible discharges to a final voltage of zero, eliminating the energy investment by external power sources. Without an external power source and membranes, the FeHCF/EDA-YP80F full cell achieves an average power density of 110 mW m −2 and energy density of 117 J m −2 over 150 cycles under the 1-0.01 M NaCl salinity gradient. Under a high salinity gradient involving hypersaline solutions, i.e. , 5-0.01 M NaCl, a remarkably high average power density of 218 mW m −2 and energy density of 305 J m −2 are demonstrated over 50 cycles. A charge-free and membrane-free hybrid capacitive mixing (H-CapMix) system for salinity gradient energy harvesting with EDA-YP80F as a capacitive anode for Cl − absorption and FeHCF as a battery-type cathode for Na + incorporation.