Harvesting Energy from Salinity Differences Using Battery Electrodes in a Concentration Flow Cell

Abstract

Salinity-gradient energy (SGE) technologies produce carbon-neutral and renewable electricity from salinity differences between seawater and freshwater. Capacitive mixing (CapMix) is a promising class of SGE technologies that captures energy using capacitive or battery electrodes, but CapMix devices have produced relatively low power densities and often require expensive materials. Here, we combined existing CapMix approaches to develop a concentration flow cell that can overcome these limitations. In this system, two identical battery (i.e., faradaic) electrodes composed of copper hexacyanoferrate (CuHCF) were simultaneously exposed to either high (0.513 M) or low (0.017 M) concentration NaCl solutions in channels separated by a filtration membrane. The average power density produced was 411 ± 14 mW m–2 (normalized to membrane area), which was twice as high as previously reported values for CapMix devices. Power production was continuous (i.e., it did not require a charging period and did not vary during each step of a cycle) and was stable for 20 cycles of switching the solutions in each channel. The concentration flow cell only used inexpensive materials and did not require ion-selective membranes or precious metals. The results demonstrate that the concentration flow cell is a promising approach for efficiently harvesting energy from salinity differences.

An Asymmetric Iron‐Based Redox‐Active System for Electrochemical Separation of Ions in Aqueous Media

“…This technique was adapted from previously reported non‐covalent functionalization methods. [ 38b,44,73 ] Conductive poly(vinylferrocene) composites were used as the working anodes. PVFc‐CB electrodes were made with 150 µL of a dispersion containing 3 mg PVFc, 3 mg CB, and 1 mg poly(vinyldienefluoride) (PVDF) per 1 mL N , N ‐Dimethylformamide (DMF).…”

Electrical power production from low-grade waste heat using a thermally regenerative ethylenediamine battery

“…External resistances were switched every 4 min from open circuit to a minimum of 1.4 U. Both current density (i=U/RA, Am -2 ; i: current density, U: voltage, R: external resistance, A: surface area), and power density (P=U 2 /RA, Wm -2 ) were normalized to a single electrode projected surface area (1.6 cm 2 ) [23]. The total charge transferred over the entire cycle was calculated by integrating the currentetime profile Q = ∫ I dts, where Q is the total charge (C), I the current (A), and ts time (s).…”

Intercalation into a Prussian Blue Derivative from Solutions Containing Two Species of Cations

“…This open structure leads to a relatively low charge density, ideally 86 mAh g −1 for NiHCF; on the other hand, it makes intercalation easy, leading to a fast charging/discharging rate . For these features, Prussian blue derivatives have been proposed for aqueous and nonaqueous metal‐ion batteries, for lithium recovery from brines, and for energy production from salinity differences …”

“…The ability of intercalation materials to store cations upon electrical chargingh as been exploited in new,p romising techniques in which ions are captured from as olutionand released into ad ifferent one. This electrochemical ion pumping has been proposed for water desalination; [1] concentrating lithium salts; [2][3][4][5] and application in the mixing entropyb attery, [6][7][8][9][10] which, analogously to capacitive mixing, [11][12][13] produces clean electricale nergy by capturing salt from sea water and releasing it into river water.T hese applications could address some major worldwide concerns,i ncluding fresh-water shortage due to population growth, [14] availability of lithium, [15] and environmental pollution occasioned by use of fossil fuels. Intercalation materials have also been used in batteries;arecent application is for batteries based on mixed aqueous electrolytes.…”

“…[20] For these features, Prussian blue derivatives have been proposed for aqueous [1,23,25,26] and nonaqueous [27,28] metal-ion batteries, for lithium recovery from brines, [27,28] and for energy production from salinity differences. [8][9][10] The process of ion intercalation in Prussian blue derivatives is not selective;i ntercalation of lithium, sodium, potassium, rubidium, caesium,a nd ammonium [22,26,28,29] has been reported. Intercalation of di-and trivalenti ons is also possible and has been reported in the literature for aqueous zinc-ionb atteries and proposed separation of ions.…”