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Another abundant source of renewable energy exists in the oceans, where the chemical energy released from the mixing of seawater and river water is known as salinity gradient energy or blue energy. Salinity gradient energy is a sustainable, clean and renewable energy source that produces electricity without emitting greenhouse gasses or other pollutants. In this work, we constructed a new salinity gradient energy extraction device by preparing V 2 O 5 in a very simple way by controlling H 2 O/C 2 H 5 OH ratio in hydrothermal process and using the V 2 O 5 as an anode to obtain salinity gradient energy by utilizing the salinity change of the solution and thus the potential difference power generation. The results show that ethanol forms hydrogen bonds or van der Waals forces with the layered material, which enters the interlayer to enlarge the spacing between the layers of V 2 O 5 and further increase the electrochemical properties of V 2 O 5. The maximum energy density produced by the device was 6.29 J g−1 after one complete cycle. The device is environmentally friendly with low cost, easy to synthesize raw materials and does not use ionic membranes, which provides a new way to harvest the salinity gradient energy. [ABSTRACT FROM AUTHOR]

Abstract The globally extractable salinity gradient (SG) energy from the mixing of seawater and river water is estimated to be 3% of worldwide electricity consumption. Here we applied carbonized peat moss (CPM) electrodes to a capacitive concentration flow cell that is capable of harvesting SG energy based on the capacitive double layer expansion (CDLE) together with the Donnan potential. The electrodes were made from the visually inexhaustible peat moss by a facile and environmental benign pyrolysis process. With two identical CPM electrodes and a cation-exchange membrane, the cell produced a peak power density of 5.33 W m−2 and an average power density of 950 mW m−2, the highest ever reported for CDLE-based techniques, using synthetic seawater (30 g L−1 NaCl) and river water (1 g L−1 NaCl). The excellent performance was a result of the macroporous structure of the CPM electrodes, the assistance of Donnan potential, and the double-channel structure of the cell. This system was durable as it could extract energy from highly saline water (300 g L−1 NaCl) and it still worked well after 100 cycles. This study provides a new method to efficiently and continuously harvest SG energy based on the CDLE without an external charge. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) is a promising technology to simultaneously generate electricity and degrade pollutants in wastewater using salinity gradient energy. The present study focuses on the degradation of ammonia and simultaneous generation of electricity by RED stacks. The results indicated that increasing the chloride concentration in the electrode rinse solution, salinity gradient, and flow rate of the electrode rinse and saline solutions can enhance the output current of RED and ammonia removal rate. The maximum ammonia removal and output power density with RED was 98% and 0.06 W/m 2 , respectively, while the optimal flow rate of electrode rinse and saline solutions was 250 mL/min and 50 mL/min, respectively. In the electrode rinse solution, active chlorine was generated in the anode chamber and degraded ammonia, which followed the indirect oxidation mechanism and made the main contribution to ammonia removal. A small quantity of monochloramine and dichloroamine were generated as intermediate oxidation products in the process, indicating that ammonia was chlorinated in a stepwise process and finally converted into nitrogen. These findings prove the feasibility of simultaneous electricity generation and ammonia removal, and pave the way for a new application of RED technology. [ABSTRACT FROM AUTHOR]

Given the considerable amount of energy dissipated in the salinity gradient at the point where a river flows into the sea, we investigate the technology of capacitive mixing (CapMix), an attractive technology for generating electrical power from this gradient. We determine the performances of multiple wire-shaped electrode pairs connected either in series or in parallel in a CapMix system. The bundles of pairs were immersed in synthetic river and seawater. Pairs connected in parallel and placed next to each other allowed for 18% more energy extraction than the total energy extracted by the same number of pairs individually. An even higher additional energy gain is possible if contact resistances are further minimized. The improvement is due to the additional flow paths for ions between electrode pairs in parallel connection, reducing the total internal resistance. The highest power density achieved (in terms of the mass of activated carbon material used) was 2.7 mW/g, which was higher than the power densities that have been achieved previously using a flat plate CapMix cell (1.26 mW/g) and a wire electrode cell (0.34 mW/g). The lower ohmic resistance in the parallel system was identified using a current distribution model and experimental measurements. [ABSTRACT FROM AUTHOR]

Abstract: Salinity gradients could be a great source of energy in the future. Capacitive energy extraction based on Donnan Potential (CDP) is a new technique to directly convert this energy into electricity. CDP uses a supercapacitor-like device combining ion exchange membranes and capacitive materials to adsorb and desorb ions with the Donnan Potential of the membranes as only driving force. The resulting current can be extracted through an external load. In this study, traditional electrochemical techniques: galvanostatic charge–discharge and cyclic voltammetry were used to investigate intrinsic properties of this open system. This study demonstrates the feasibility to characterize the capacitive behavior of the cell in low concentration (0.5M). Presence of membranes, as well as the possibility of having the electrolyte flowing through the cell was investigated. In the studied cell, the presence of membranes showed a limitation by the anion exchange membrane at low current densities but no effect at high current densities. The flow rate did not influence the capacitance of the system either. [Copyright &y& Elsevier]

• The Janus membranes composited with 2D lamellar MXene/3D network bacterial nanocellulose nanofiber were developed. • The preferred transport direction of the cations flows was identical under the different electrokinetic situations. • The implementation of artificial seawater and river water on the fully abiotic MXene/BNC Janus membrane can achieve an outstanding output power density of 0.91 Wm−2. In the field of nanofluidic osmotic power generators, it has been an ultimate but seemingly distant goal to controllably fabricate the different-dimensional confined space including slits, network, nanochannels or their composition to control the ion transport. We demonstrated ion transport behaviors through ultimately 2D lamellar MXene/3D network bacterial nanocellulose nanofiber composite Janus membranes under the different transmembrane concentration gradient. The heterogeneous multilayers Janus membrane comprised effectively stacked hydrophobic MXene to hydrophilic bacterial nanocellulose (BNC). The asymmetric cations transport phenomena were explained in terms of asymmetric surface charges polarization in the confined space. Our results provided a facile and general strategy for studying the effects of membrane-scale confinement, which was important for the development of biomimetic energy conversion, ionic seizing, chemical sensing and other nanoscale technologies. We fabricate a bilayered heterogeneous MXene/BNC Janus membrane and demonstrate the asymmetric cations transportation phenomena in the confined slits therein. The cations prefer to transport from 2D silts to 3D network under electric field and the transmembrane concentration gradient [Display omitted] [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) technology is a direct and effective technology for power generation by harvesting salinity gradient energy (SGE). The output current is one of the key operating parameters to control the power output of a RED stack. This research investigates the specific effect of the current-induced ion transfer on each electrical resistance component of the RED stack. The results showed that the internal resistance of the RED stack decreases with the increase of the current, because larger ion transfer induced by larger current would initiate the variation of concentrations of the feeding concentrated and diluted solutions along the flow path. It is worth highlighting that the ohmic resistance of the diluted solution component takes the dominant proportion in the total ohmic resistance of a RED stack, which decreases significantly with the increase of current. The non-ohmic resistance also decreases with the current increases. Therefore, the internal resistance of RED stack depends on the current. Moreover, it is found that the polarization curve and power density curve can be in good accordance with the experimental data if the influence of current on internal resistance is taken into consideration. The energy efficiency increases first and decreases with the current increase. The maximal energy efficiency of 3.4% was achieved when the RED stack operated in the maximum power density of 3.67 W/m2 at the current density of 44.9 A/m2. The coulombic efficiency increases with the increase of the current. The residual ratio of the SGE in effluent decreases with the increase of the current. [ABSTRACT FROM AUTHOR]

Salinity gradient (SG) energy is a large untapped energy source available worldwide. Here we applied MoS 2 with tunable interlayer spacing to a concentration flow cell for efficient SG energy recovery. By expanding the interlayer from 0.63 nm to 0.96 nm, the ion diffusion resistance was significantly reduced and the pseudocapacitance was largely promoted. These enhanced electrochemical properties resulted in a superior performance of the concentration flow cell on SG energy extraction. The cell with interlayer-expanded MoS 2 electrodes produced 11 times of the average power density compared with the cell with original MoS 2 electrodes when using model seawater and river water solutions. The interlayer-expanded MoS 2 was also among the most durable materials for SG energy harvesting as it allowed the cell to run over 120 cycles and work efficiently at varying salinity concentrations. When provided with brine water (300 g L−1 NaCl) and fresh water (1 g L−1 NaCl), the cell yielded a peak power density of 16 W m−2, an average power density of 1.4 W m−2, and an energy density of 181 J m−2. All these evidences support that the interlayer-expanded MoS 2 is a prospective material for SG energy recovery in concentration flow cells. [ABSTRACT FROM AUTHOR]

Salinity gradient (SG) energy is a large, renewable, and clean energy source, which naturally exists between river water and seawater and can also be created by engineering processes. Here, bismuth oxychloride (BiOCl) electrodes was used for efficient SG energy recovery in a chloride-ion concentration flow cell (Cl-CFC) based on a new mechanism, that is, chloride ion (Cl−) intercalation/deintercalation. Compared to previous Cl-CFC with BiCl 3 electrodes based on Cl− extraction/insertion (3.17 W m−2), the peak power density of the cell with BiOCl electrodes (4.36 W m−2) was higher under the same testing conditions when using synthetic river water (1 g L−1 NaCl) and seawater (30 g L−1 NaCl). Further investigations demonstrated that the relatively higher power density was attribute to the faster kinetics of Cl− intercalation/deintercalation at BiOCl electrodes than that of Cl− extraction/insertion at BiCl 3 electrodes. In addition, three BiOCl electrodes with different carbon black ratios (CB, 10%, 20% and 30%) were also prepared and examined in this study. Compared to BiOCl/10%CB and BiOCl/30%CB electrodes, the lower charge transfer and ion diffusion resistances, larger ion storage capacities and higher cell open circuit voltages of the BiOCl/20%CB electrodes were all beneficial to its higher power output. [ABSTRACT FROM AUTHOR]