Sodium-ion concentration flow cell stacks for salinity gradient energy recovery: Power generation of series and parallel configurations

Surveying Manganese Oxides as Electrode Materials for Harnessing Salinity Gradient Energy

“…The cutoff voltage value was based on previous work in our lab that examined its effect on observed peak and average power densities . We could continue to produce electricity over multiple cycles by periodically switching the flow paths of the sodium chloride solutions, consistent with previous studies using the same cell architecture with different electrode materials. , …”

“…To compare the electrical power density that each manganese oxide could produce, we fabricated composite manganese oxide electrodes and tested them in a symmetrical, dual-channel concentration flow cell (Figure a). We used this cell design because the design was previously shown to generate the highest electrical power densities when harvesting salinity gradient energy using electrode-based reactions. − The cell contained two identical manganese oxide composite electrodes that were exposed to two waters with different sodium chloride concentrations (30 g/L, 0.5 M and 1 g/L, 0.02 M) flowing at 15 mL/min (hydraulic retention time = 0.14 s). The two flow channels were separated by an anion exchange membrane.…”

“…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. − …”

“…The performances of salinity gradient energy technologies are usually compared in terms of electrical power densities (i.e., the rate of electricity production normalized to the area of a membrane or electrode) . While early electrode-based systems yielded low power densities (0.03–0.2 W/m 2 ) relative to membrane-based systems (∼1–10 W/m 2 for freshwater/seawater), recent electrode-based studies have generated comparable values (3.3–3.8 W/m 2 ). , Achievable power densities have increased as a result of improved cell design, the introduction of a single ion exchange membrane to increase the cell voltage, and more effective electrode materials. ,, A major advance in electrode materials has derived from the transition from purely capacitive carbon-based electrode materials to electrode materials that charge via a combination of capacitive and faradaic mechanisms (e.g., Prussian Blue analogs and manganese oxides). ,,− Materials that undergo faradaic reactions are often referred to as pseudocapacitive when the faradaic reaction rates are sufficiently fast that they produce capacitor-like current–potential relationships. − …”

Electrochemical cell recharging by solvent separation and transfer processes

“…Anodic and cathodic reactions are reverse redox reactions of the same redox couple (R and O). Although this system appears to be similar to general concentration cells 24 – 27 , the installation of the TS leads to differences in the solvation states of R and O between H-TS and L-TS and contributes to a larger cell voltage. Note that the directions of the reactions are dependent on the components applied as a redox couple, MS, TS or other solutes.…”