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

Abstract

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 ) and exhibited a notable power output (97 mW m ) 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.

Electrochemical Systems for Renewable Energy Conversion from Salinity and Proton Gradients

“…, which points a new direction in this technology. 81 Nevertheless, future investigations concerning self-discharge processes in the double layer of this system appear to be necessary to improve its efficiency. Energy expenditure during the pre-concentration process, energy loss due to diminished concentration gradient after successive charge/discharge processes, and reversibility of the anion selective electrode are parameters that require further developments in order to make the MEB system viable.…”

Electrochemical Analysis of High-Performance Flow-Electrode Capacitive Mixing (F-CapMix) under Different Operating Conditions

“…Specifically, Porada et al evaluated the energy production potential of the F-CapMix system under various system configurations, including CO 2 in water, CO 2 in monoethanolamine, and the establishment of a salinity gradient using flat-plate cell and hollow cylindrical cell configurations. For the upscaling of the F-CapMix technology, improving its power density is important; previously reported power density values of F-CapMix are in the microwatt scale, compared to those of the conventional CapMix system (milliwatt scale). , These low power density values of the F-CapMix cell can be attributed to inefficient charge percolation between the activated carbon (AC) particles in the flow-electrode with a lower AC content, compared with the conventional solid electrode in the CapMix system. Further, the power density of the F-CapMix system primarily depends on ion flux through IEMs and the rate of the electrochemical reaction on the electrode, which converts ionic flux to electrical current.…”

Surveying Manganese Oxides as Electrode Materials for Harnessing Salinity Gradient Energy

“…It is estimated that the global amount of harvestable electricity from mixing freshwater with seawater is 8800 TW·h per year, which is equal to 40% of the worldwide electricity production (21 600 TW·h in 2012) . Energy can also be obtained using more saline waters, such as hypersaline lakes and reject brines from desalination plants. − Currently, the two most extensively studied methods used to harvest salinity gradient energy are pressure retarded osmosis (PRO) and reverse electrodialysis (RED). − However, both technologies require selective membranes that either foul rapidly (PRO) or are prohibitively expensive (RED). ,, To overcome these membrane-related issues, researchers have begun studying electrochemical systems that harvest salinity gradient energy using electrode-based electrochemical reactions. − …”