Concentration Flow Cells Based on Chloride-Ion Extraction and Insertion with Metal Chloride Electrodes for Efficient Salinity Gradient Energy Harvest

Abstract

Salinity gradient (SG) is a natural and renewable energy source existing in estuaries, and can also be produced during various desalination and industrial processes. Here, a new method is proposed to efficiently recover SG energy based on chloride-ion (Cl − ) extraction and insertion with metal chloride electrodes and the Donnan potential over a cation-exchange membrane in a concentration flow cell. Three different metal chloride electrodes (BiCl 3 , CoCl 2 , and VCl 3 ) were investigated in the cell, and their properties after discharging in 30 g L −1 (seawater) and 1 g L −1 (river water) NaCl solutions were studied by cyclic voltammetry, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy. The cell with BiCl 3 electrodes yielded the largest power density (max. = 3.17 W m −2 ) compared to that of CoCl 2 and VCl 3 electrodes, which was higher than those of most previous technologies for SG energy recovery. Fast Cl − extraction and insertion processes were observed on BiCl 3 electrodes due to small charge transfer resistance and Cl − diffusion resistance. BiCl 3 was reduced to metal Bi as Cl − released from the electrode to river water, while metal Bi was oxidized to BiCl 3 as Cl − inserted into the electrode from seawater.

Facile Designed Manganese Oxide/Biochar for Efficient Salinity Gradient Energy Recovery in Concentration Flow Cells and Influences of Mono/Multivalent Ions

“…For comparison, unmodified rice husk biochar was made in the same way but without presoaking of the rice husks in KMnO 4 solution, which are designated as Bio400, Bio500, Bio600, and Bio700. The procedure for electrode preparation was reported in our previous studies, , and the physiochemical and electrochemical characterization methods of prepared electrodes are shown in the Supporting Information.…”

“…The configuration and performance tests of CFCs were similar to our previous studies (Figure S1). , The two identical water chambers of CFCs were 0.67 cm × 3 cm × 127 μm. To test the performance of CFCs with different MnO x /biochar electrodes, high-concentration (HC, 30 g L –1 or 0.513 M) and low-concentration (LC, 1 g L –1 or 0.017 mM) NaCl solutions were used.…”

“…The solution paths could be periodically switched to recharge the CFCs to continuously generate power. 11 Later, bismuth chloride (BiCl 3 ), 12 bismuth oxychloride (BiOCl), 13 molybdenum disulfide (MoS 2 ), 14 and carbonized peat moss 15 were also employed for efficient SG energy harvest in CFCs. However, the preparations of CuHCF, BiCl 3 , BiOCl, and MoS 2 were relatively complex with high costs.…”

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

“…the Nernst equation. 26 The electrolyte conductivity corresponding to different NaCl concentrations is shown in Fig. 3e, ranging from 1.331 mS cm −2 at 0.01 M to 250.6 mS cm −2 at 5 M.…”

“…While it does not require membranes to operate, the demonstrated power densities of membrane-free CapMix systems are too low to be economically competitive. In a broader sense, CapMix technology embraces ve device types, which are capacitive double layer expansion (CDLE), 16,18,20,22,23 capacitive Donnan potential (CDP), 4,[24][25][26][27][28] mixing entropy battery (MEB), 4,6,19,21,26,[29][30][31] concentration ow cell (CFC), 4,19,26,29,30 and hybrid CapMix (H-CapMix). 32,33 A typical CDLE device uses two activated carbon electrodes and produces the voltage rise resulting from the change of electric double layer (EDL) thickness under different salinities.…”