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Featured Application: The developed methodology enables the rapid fabrication of customized lab-scale reactors, optimizing their design and manufacturing. Beyond desalination, this approach is valuable in the early R&D stages for other electrochemical flow reactors, such as fuel cells, bio-batteries, microfluidic devices, and electrolyzers. In response to the growing demand for potable water, this study presents a practical methodology for designing and fabricating a hybrid desalination system that integrates reverse electrodialysis and electrodialysis using 3D-printing technology. The hybrid system combines the energy generation potential of RED with the salt removal capabilities of ED, reducing energy consumption. Customized reactors were designed to enhance flow distribution and ion exchange, with computational fluid dynamics simulations validating the hydrodynamic performance. The reactors were fabricated using 3D printing, allowing rapid, cost-effective production, with functional reactors constructed in under 24 h. The system achieved a 15% reduction in salt concentration within one hour, with a specific energy consumption of 0.1388 Wh/m3 and a water recovery rate of 50%. These results demonstrate the functionality of the RED-ED hybrid system for achieving energy savings and performing water desalination. This methodology provides a scalable and replicable solution for water treatment applications, especially in regions with abundant salinity gradients and limited freshwater resources, while offering a multidisciplinary approach that integrates physicochemical and engineering principles for effective device development. [ABSTRACT FROM AUTHOR]

Industry, agriculture, and a growing population all have a major impact on the scarcity of clean‐water. Desalinating or purifying contaminated water for human use is crucial. The combination of thermal membrane systems can outperform conventional desalination with the help of synergistic management of the water‐energy nexus. High energy requirement for desalination is a key challenge for desalination cost and its commercial feasibility. The solution to these problems requires the intermarriage of multidisciplinary approaches such as electrochemistry, chemical, environmental, polymer, and materials science and engineering. The most feasible method for producing high‐quality freshwater with a reduced carbon footprint is demanding incorporation of industrial low‐grade heat with membrane distillation (MD). More precisely, by using a reverse electrodialysis (RED) setup that is integrated with MD, salinity gradient energy (SGE) may be extracted from highly salinized MD retentate. Integrating MD‐RED can significantly increase energy productivity without raising costs. This review provides a comprehensive summary of the prospects, unresolved issues, and developments in this cutting‐edge field. In addition, we summarize the distinct physicochemical characteristics of the membranes employed in MD and RED, together with the approaches for integrating them to facilitate effective water recovery and energy conversion from salt gradients and freshwater. [ABSTRACT FROM AUTHOR]

Salinity gradient energy presents a promising opportunity for renewable energy, gaining significant interest in the sustainable power sector. This article presents an overview of the application of ion exchange membranes and reverse electrodialysis techniques to harness energy from salinity gradients in seawater, employing anthropomorphic terminology to enhance understanding. The main focus lies in the utilization of ion exchange membrane technology for power generation, with a particular emphasis on its current implementation status and underlying operational principles. The research aims to enhance readers' comprehension of salinity gradient energy in seawater and promote awareness of "energy security" through the use of descriptive language. [ABSTRACT FROM AUTHOR]

Blue energy obtained by salinity gradient can be generated by mixing two saline solutions having different salt concentrations. According to researchers working in this area, about 80% of the current global electricity demand could potentially be covered by this energy source. There are basically two membrane technologies so-called pressure-retarded osmosis (PRO) and reverse electrodialysis (RED) that are capable to generate electrical energy from salinity gradient. The pressure driven PRO process is more suitable for energy generation from highly concentrated brines. However, RED is more favorable for power generation by mixing seawater and river water. In RED process, ion exchange membranes (IEMs) placed between two electrodes in a stack were employed for transport of ions. Thus, an electrical current is obtained at the electrodes by electron transport through redox reactions. This review gives an overview of RED as a pioneering technology for salinity gradient energy (SGE) generation. The review summarizes the recent improvements of IEMs employed for RED studies, membrane fouling and RED stack design. [ABSTRACT FROM AUTHOR]

Natural salinity gradients are a promising source of so-called blue energy, a renewable energy source that utilizes the free energy of mixing for power generation. One promising blue energy technology that converts these salinity gradients directly into electricity is reverse electrodialysis (RED). Used at its full potential, it could provide a substantial portion of the worlds electricity consumption. Previous theoretical and experimental works have been done on optimizing RED devices, with the latter often focusing on precious and expensive metal electrodes. However, in order to rationally design and apply RED devices, we need to investigate all related transport phenomena─especially the fluidics of salinity gradient mixing and the redox electrolyte at various concentrations, which can have complex intertwined effects─in a fully functioning and scalable system. Here, guided by fundamental electrochemical and fluid dynamics theories, we work with an iron-based redox electrolyte with carbon electrodes in a RED device with tunable microfluidic environments and study the fundamental effects of electrolyte concentration and flow rate on the potential-driven redox activity and power output. We focus on optimizing the net power output, which is the difference between the gross power output generated by the RED device and the pumping power input, needed for salinity gradient mixing and redox electrolyte reactions. We find through this holistic approach that the electrolyte concentration in the electrode rinse solution is crucial for increasing the electrical current, while the pumping power input depends nonlinearly on the membrane separation distance. Finally, from this understanding, we designed a five cell-pair (CP) RED device that achieved a net power density of 224 mW m-2 CP-1, a 60% improvement compared to the nonoptimized case. This study highlights the importance of the electrode rinse solution fluidics and composition when rationally designing RED devices based on scalable carbon-based electrodes.

Background: Using novel technologies and solutions is crucial for producing clean water. There are different ways to remove dissolved salts from water. Methods: This study aimed to analyze the effect of an external force (EF) on the morphology of channels, the dispersion of particles, and the permeability of substances via carbon nanotubes in reverse electrodialysis. It was done using a computer simulation that studied the movement of molecules. This research aimed to study the effect of EF on the dispersion of particles and permeability of substances via carbon nanotubes using a reverse electrodialysis approach. The results show that increasing the EF from 0.0001 to 0.0005 eV/Å increased the electric current and fluid flow intensity from 5.31 e/ns and 211.31 atom/ns to 5.62 e/ns and 263.01 atom/ns. Moreover, the density decreased from 4.83 to 4.66 atom/nm3. Furthermore, the number of broken hydrogen bonds increased from 116 to 166. Significant findings: By understanding the effect of EF on particle movement and material passage through carbon nanotubes, researchers can optimize the design of reverse electrodialysis systems to enhance their performance. This can lead to more effective and cost-efficient water treatment solutions, crucial for producing clean water.

In the climate changing context, hydrogen is leading the energy transition path. The present work focuses on the green hydrogen production exploiting salinity gradients via Reverse Electrodialysis (RED), in short-circuit condition (RED SC), and Assisted RED (ARED), studied for the first time in hydrogen production as an improvement of the low current densities generated by RED. An extensive experimental campaign was carried out by feeding a RED stack with different salinity gradients and testing short-circuit-RED and Assisted RED operative conditions. Hydrogen was produced successfully with ∼100 % Faradic Efficiency (FE) and productivity up to 1.7 mol h−1 m−2. Also, the technology was compared with similar technologies and with the most established state-of-the-art electrolysers to identify advantages and disadvantages of the proposed route. Finally, a preliminary economic analysis was carried out and a minimum Levelized Cost of Hydrogen (LCOH) of 3.2 € kg−1 H2 was found, thus leaving room for further studies. [Display omitted] • Green hydrogen production from salinity gradient by Reverse Electrodialysis • Production boosting via Assisted Reverse Electrodialysis (A)RED for the first time • Investigation of hydrogen production under different operating conditions • Comparison of the proposed electrolyser with the state-of-the-art • Preliminary economic assessment with calculation of the Levelized Cost of Hydrogen [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) is one of the methods able to generate energy from the salinity gradient between sea- and river water. The technique is based on the diffusion of ions through membranes that specifically allow either cations or anions to pass through. This ion current is converted into an external electric current at electrodes via suitable redox reactions. Seawater contains mainly eight different ions and the description of transport phenomena in membranes in classical terms of isolated species is not sufficient because the different particles have different velocities—in the same direction or opposite—in the same membrane. More realistic is the Maxwell–Stefan (MS) theory that takes all interactions between the different particles in account; however, such a model is complex and validation is difficult. Therefore, a simplified system is used with solely NaCl in solution, using only 9 diffusivities in the calculation. These values are estimated from the literature and are applied to an MS model of the RED process. Using experimental data of NaCl and water transport as well as power density, these diffusivities are adapted in the MS model. Reliable values for the diffusivities were obtained for the following three interactions: H2O–Na+, H2O–Cl− and Na+–Cl−. [ABSTRACT FROM AUTHOR]

In traditional reverse electrodialysis (RED) stacks, the output power is severely lost due to the shadow effect caused by the nonpermselective spacers. To inhibit the spacer shadow effect, a design on ion‐permselective woven net spacer is proposed. By combining the linear sweep voltammetry and electrochemical impedance spectroscopy methods, the effectiveness of permselective woven net spacer is validated together with the shadow effect and concentration polarization measured quantitatively. Additionally, their influence on stack resistance and power production is investigated under various factors. When contrasted to nonpermselective spacers, the use of permselective woven net spacers reduces the spacer shadow effect by 90% whereas also exacerbating the concentration polarization. This results in a higher power density due to a dramatic reduction in resistance. However, compared with permselective spacers, the permselective woven net spacers increase the power density due to its weaker concentration polarization. The factors including the solution concentration, temperature, and spacer thickness have a considerable influence on the power production of stack. Especially, increasing the concentration of concentrated solution alone is most beneficial to improving the output power while the impact of spacer thickness is the weakest. [ABSTRACT FROM AUTHOR]

Blue energy obtained by salinity gradient can be generated by mixing two saline solutions having different salt concentrations. According to researchers working in this area, about 80% of the current global electricity demand could potentially be covered by this energy source. There are basically two membrane technologies so-called pressure-retarded osmosis (PRO) and reverse electrodialysis (RED) that are capable to generate electrical energy from salinity gradient. The pressure driven PRO process is more suitable for energy generation from highly concentrated brines. However, RED is more favorable for power generation by mixing seawater and river water. In RED process, ion exchange membranes (IEMs) placed between two electrodes in a stack were employed for transport of ions. Thus, an electrical current is obtained at the electrodes by electron transport through redox reactions. This review gives an overview of RED as a pioneering technology for salinity gradient energy (SGE) generation. The review summarizes the recent improvements of IEMs employed for RED studies, membrane fouling and RED stack design.

Salinity gradient power (SGP) by reverse electrodialysis is a promising method for converting SGP into electricity. Instead of the conventional approach of using seawater and freshwater, an alternative method involves using highly concentrated salt solutions (brines) alongside seawater or brackish water. Key factors influencing SGP via reverse electrodialysis (SGP-RE) include the properties of ion exchange membranes, particularly their thickness. This paper outlines a practical experimental set-up that uses both a cation membrane (CM) and an anion membrane (AM). The system is configured with three compartments: two outer compartments filled with highly concentrated brine (HIGH) and a central compartment containing a lower concentration salt solution (LOW), akin to seawater. The compartments are separated by a CM on one side and an AM on the other. The ion transport rate from the HIGH compartments to the central LOW compartment allows for determining the overall ion transport coefficient for thin membranes. Measurements of ion flux and electrochemical voltage under dynamic equilibrium conditions also enable the estimation of the SGP-RE power density (W/m2). By controlling the temperature of the HIGH and LOW solutions, this experiment further investigates the significant impact of temperature on ion transport characteristics.

In response to the growing demand for potable water, this study presents a practical methodology for designing and fabricating a hybrid desalination system that integrates reverse electrodialysis and electrodialysis using 3D-printing technology. The hybrid system combines the energy generation potential of RED with the salt removal capabilities of ED, reducing energy consumption. Customized reactors were designed to enhance flow distribution and ion exchange, with computational fluid dynamics simulations validating the hydrodynamic performance. The reactors were fabricated using 3D printing, allowing rapid, cost-effective production, with functional reactors constructed in under 24 h. The system achieved a 15% reduction in salt concentration within one hour, with a specific energy consumption of 0.1388 Wh/m3 and a water recovery rate of 50%. These results demonstrate the functionality of the RED-ED hybrid system for achieving energy savings and performing water desalination. This methodology provides a scalable and replicable solution for water treatment applications, especially in regions with abundant salinity gradients and limited freshwater resources, while offering a multidisciplinary approach that integrates physicochemical and engineering principles for effective device development.

Artificial nanofluidic networks are emerging systems for blue energy conversion that leverages surface charge‐derived permselectivity to induce voltage from diffusive ion transport under salinity difference. Here the pivotal significance of electrostatic inter‐channel couplings in multi‐nanopore membranes, which impose constraints on porosity and subsequently influence the generation of large osmotic power outputs, is illustrated. Constructive interference is observed between two 20 nm nanopores of 30 nm spacing that renders enhanced permselectivity to osmotic power output via the recovered electroneutrality. On contrary, the interference is revealed as destructive in two‐dimensional arrays causing significant deteriorations of the ion selectivity even for the nanopores sparsely distributed at an order of magnitude larger spacing than the Dukhin length. Most importantly, a scaling law is provided for deducing the maximal membrane area and porosity to avoid the selectivity loss via the inter‐pore electrostatic coupling. As the electric crosstalk is inevitable in any fluidic network, the present findings can be a useful guide to design nanoporous membranes for scalable osmotic power generations. [ABSTRACT FROM AUTHOR]

OBJECT. Experimental studies on optimization of the output electrical and mass transfer characteristics of the reverse electrodialysis process.METHODS. System analysis techniques were used in this work and a mathematical model was developed to describe the movement of water streams and the concentrations of substances in them. The equipment involved, designed for experimental and industrial testing of the proposed technologies with technical characteristics of the developed apparatuses and installations, is described.RESULTS. RED (reverse electrodialysis) is a new membrane technology for renewable energy production using salinity gradients. The ultimate goal of RED is to achieve the highest possible value of power density, which depends on several parameters related to the intrinsic electrochemical characteristics of the membranes, stack configuration (number of cell pairs, channel length), hydrodynamics, nature of the working solutions (ionic composition, concentration), and others. The paper presents experimental studies on the influence and modeling of various parameters of the reverse electrodialysis operation on the output electrical characteristics of the system.CONCLUSIONS. It is shown that the system output power is significantly influenced by the composition of solutions in the near-electrode chambers, external load and internal resistance, concentrations of working solutions and time of the experiment. The maximum electrical efficiency was 56% (power density 0.34 W/m2) in semi-industrial electrodialysis reverse electrodialysis experiments using model NaCl solutions, K3Fe(CN)6/K4Fe(CN)6 and Chinese 0.6 mm thick IONSEP membranes.

Abstract Artificial nanofluidic networks are emerging systems for blue energy conversion that leverages surface charge‐derived permselectivity to induce voltage from diffusive ion transport under salinity difference. Here the pivotal significance of electrostatic inter‐channel couplings in multi‐nanopore membranes, which impose constraints on porosity and subsequently influence the generation of large osmotic power outputs, is illustrated. Constructive interference is observed between two 20 nm nanopores of 30 nm spacing that renders enhanced permselectivity to osmotic power output via the recovered electroneutrality. On contrary, the interference is revealed as destructive in two‐dimensional arrays causing significant deteriorations of the ion selectivity even for the nanopores sparsely distributed at an order of magnitude larger spacing than the Dukhin length. Most importantly, a scaling law is provided for deducing the maximal membrane area and porosity to avoid the selectivity loss via the inter‐pore electrostatic coupling. As the electric crosstalk is inevitable in any fluidic network, the present findings can be a useful guide to design nanoporous membranes for scalable osmotic power generations.

Harvesting clean and renewable osmotic energy through reverse electrodialysis (RED) technology offers a promising solution to address energy crisis problems. The development of nanochannel membranes constructed from diverse nanomaterials plays a crucial role in enabling efficient osmotic energy conversion. In this review, first an overview of the mechanism of the RED process is provided and the physicochemical properties of nanomaterials, covering 0D, 1D, and 2D nanomaterials, and the osmotic conversion performances of the constructed nanochannel membranes. Then, the relationship between chemical properties and structural features of nanochannel membranes is specifically highlighted, including surface charge property and geometric structure, and osmotic energy conversion efficiency. Additionally, the introduction of external stimuli, such as light, temperature, pH, external pressure, and changes in electrolyte environments, are also discussed. Finally, the research directions and future challenges in the field of osmotic energy harvesting using nanochannel membranes based on nanomaterials are presented. The focus is on refining the osmotic conversion mechanism, as well as optimizing the structure design. [ABSTRACT FROM AUTHOR]

The potential of harnessing osmotic energy from the interaction between seawater and river water has been recognized as a promising, eco‐friendly, renewable, and sustainable source of power. The reverse electrodialysis (RED) technology has gained significant interest for its ability to generate electricity by combining concentrated and diluted streams with different levels of salinity. Nanofluidic membranes with tailored ion transport dynamics enable efficient harvesting of renewable osmotic energy. In this regard, anodic aluminum oxide (AAO) membranes with abundant nanochannels provide a cost‐effective nanofluidic platform to obtain structures with a high density of ordered pores. AAO can be utilized in constructing asymmetric composite membranes with enhanced ion flux and selectivity to improve output power generation. In this review, we first present the fundamental structure and properties of AAO, followed by summarizing the fabrication techniques for asymmetric membranes using AAO and other nanostructured materials. Subsequently, we discuss the materials employed in constructing asymmetric structures incorporating AAO while emphasizing how material selection and design can resist and promote efficient energy conversion. Finally, we provide an outlook on future applications and address the challenges that need to be overcome for successful osmotic energy conversion. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED), an emerging membrane-based technology, harnesses salinity gradient energy for sustainable power generation. Accurate characterization of electrical parameters in RED stacks is crucial to monitoring its performance and exploring possible applications. In this study, a DC electronic load module (DCELM) is implemented in a constant current condition (CC mode) for characterization of lab scale RED process, using a RED prototype in-house designed and manufactured (RU1), at different data capture setups (DCS), on which the total number of steps for data capture (NS) and the number of measurements per step (ρ) are the parameters that were modified to study their effect on obtained electrical parameters in RED. NS of 10, 50, and 100 and ρ of 10 and 20 were used with this purpose. The accuracy of resulting current and voltage steps can be enhanced by increasing NS and ρ values, and according to obtained results, the higher accuracy of resulting output current and voltage steps, with low uncertainty of the average output steps (AOS) inside the operational region of power curve, was obtained using a DCS of NS = 100 and ρ = 20. The developed DCELM is a low-cost alternative to commercial electronic load devices, and the proposed methodology in this study represents an adaptative and optimizable CC mode characterization of RED process. The results obtained in this study suggest that data capture conditions have a direct influence of RED performance, and the accuracy of electrical parameters can be improved by optimizing the DCS parameters, according to the required specifications and the scale of RED prototypes. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) is one of the technologies used to harness 'Blue Energy', which is generated from the controlled separation of ions between salt water and fresh water through cation and anion exchange membranes (CEM/AEM) stack with end electrodes. The spacers present in between CEM and AEM allows the flow of salt and fresh water significantly affecting the fouling and concentration polarization in the RED cell. The present work focuses on improvement in flow path design, which may be used in place of mesh spacers in order to reduce pressure drop and enhance shear stress on the surface of the membrane to reduce concentration polarization. A three‐dimensional direct numerical simulation of the Navier–Stokes equation is conducted using Fluent 14.0 to analyze four different flow field designs, including serpentine, criss‐cross, rhombus, diamond, and standard mesh spacers. The simulation predicted closely the experimental data on pressure drop for the mesh spacers available in the literature. The present study points out that the diamond type flow field design, which combines characteristics of mesh spacers and flow field plates, gives lesser pressure drop per unit length with the increase in velocity within the same range of shear stress generated in mesh spacers. In other words, net power density of RED would improve with the use of diamond type spacer flow field with the decrease in concentration polarization loss and pumping power density. [ABSTRACT FROM AUTHOR]

Problem Statement. Today, humanity is in search of new sources of energy to make the economy more sustainable, as well as the need for a transition to energy that works on the principles of Carbon-Free Technology. For the Black Sea, this is expressed in the desire for successful implementation of the program Blue Growth Accelerator, which is aimed at the introduction of innovative technologies and alternative energy sources in the energy sector of the Black Sea countries, for the development of the "Blue Economy" and the achievement of its healthy, productive and sustainable state. Salinity gradient power (SGP) is one of the new renewable energy sources. The most studied methods for obtaining SGP energy are technologies based on: Reverse Electrodialysis and Pressure Retarded Osmosis. The interaction of fresh and salt water can provide, in fact, unlimited, free and clean energy. The basis for the generation of such energy is the so-called salinity gradient that occurs when two types of water are mixed. After decades of work and numerous experiments, scientists have developed a way to use the energy of the salinity gradient to generate electricity. This type of electricity is also called "Blue Energy" by association with the color of mixing freshwater and salt water when rivers flow into the ocean. Places (estuaries or deltas), where rivers flow into the oceans and seas, have a truly enormous energy potential. The aim of this study is to identify sites in the northwestern Black Sea region with the necessary conditions for the development of Salinity Gradient Power energy, as well as to assess their potential using the example of estimating the maximum theoretical power of the Pressure Retarded Osmosis process. Research Methodology. In a PRO system, the less concentrated solution flows towards the more concentrated solution due to the positive osmotic pressure difference as long as this difference remains greater than the hydrostatic pressure difference. It is by this principle that osmotic power is produced. Theoretically available amount of energy released when mixing 1 m3 of saturated brine (5 mol/l NaCl solution) and 1 m3 of sea water (0.5 mol/l NaCl) at 293 K is 10 MJ. In the northwestern Black Sea region, along the coast between the Danube and Dnieper rivers, there are 21 limans (lagoons) of which some can be used to generate of Salinity Gradient Power. Results. The results of calculating the maximum net power showed that highest values obtained in the summer months, when the salinity in limans reaches its maximum and, consequently, its difference with the salinity of sea (river) water increases. Proceeding from maximum net power, obtained for the Western Sivash, where the salinity is maintained artificially at certain values, it can be seen that the annual amplitude has a smaller value, which provides more stable conditions. There are objects in the northwestern Black Sea region, in the waters of which, as soon as technologies become available, it will be possible to implement SGP projects. The Kuialnyk Liman, Sasyk- Sivash lake and Western Sivash have the most favorable conditions, where the highest power indicators are shown when using the sea water – hypersaline solution scheme, in which freshwater is not consumed.

The study explores the technical feasibility of using abandoned mining site wastewater, specifically acid mine drainage (AMD), as an electrode solution in a reverse electrodialysis (RED) stack for energy production. Through experiments using a RED cell with varying electrode solutions, it was determined that the system achieved a maximum power density of 0.327 W m−2cell pair (5.01 W m−2electrode) when using simple mixtures of Cu2+ and Fe2+ ions, aligning with previous research on the Fe2+/Fe3+ redox pair. Synthetic solutions mimicking AMD composition also yielded promising results. When operating the system with real AMD effluent from an abandoned mine, a slightly lower maximum power density of 0.137 W m−2cell pair was achieved, only 5.5 % lower than with synthetic AMD. An extended-duration test showed a minor increase in pH in the electrode solution, but importantly, no metal deposition occurred on the electrode surface, as the pH consistently remained below 3.5 throughout the test. These findings indicate the potential of AMD as a viable electrode solution, offering a promising avenue for further research in the development of more sustainable RED systems.

The performance of Reverse Electrodialysis (RED) stacks can be significantly degraded by the presence of divalent ions. To gain a deeper understanding of the influence of divalent ions, a RED model based on the Nernst-Planck framework was developed in this study. Using this model, a simulation study was performed when the feed solutions contain a mixture of NaCl and MgCl 2. The impact of the divalent ion Mg2+ on RED performance was examined from the perspective of ion transport. The results indicate that divalent counterions decrease membrane permselectivity and membrane potential, while increasing membrane electrical resistance by affecting ion concentrations within the membrane. The uphill transport of divalent ions occurs only when the molar fraction of divalent ions in the feed solutions is relatively low. Specifically, when the feed solution contains only MgCl 2 compared to only NaCl, the open-circuit voltage decreases by 36.2%, and the maximum gross power density decreases by 44.8%. [Display omitted] • A RED model was developed based on the Nernst-Planck framework. • Influence of divalent ions on the performance of RED was investigated. • Degradation of RED performance was examined in terms of ion transport. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis in nanochannels has become an innovative method to obtain clean energy. To enhance the power generation efficacy of the nanochannel, the finite element method was employed to model the impact of the temperature gradient on the power generation efficiency of the conical channel. The investigation primarily focused on the nanochannel structure, as well as the direction and magnitude of the solution temperature gradient. The results show that the overall power generation performance is superior for ions diffusing from the large pore end to the small pore end in the presence of a negatively charged wall surface. The nanochannel system with a negative temperature gradient shows better power generation performance than that with a positive temperature gradient under the same nanochannel parameters and solution conditions. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) is a renewable energy-generating SGE technique using energy from salinity gradients. This research investigates the effect of membrane and feed characteristics on reverse electrodialysis (RED) power generation. Some investigations on the process parameters effect for the complement of the main study were also conducted. The generated power of RED was measured using power density analysis. The experiments were performed using artificial seawater varied from 0 to 1 g/L NaCl for diluted salt water and from 0 to 40 g/L NaCl for concentrated salt water. In a study of ions type, NaCl non-pa is used to represent monovalent ions, and MgSO4 represents divalent ions. The results showed that the highest voltage generation is 2.004 volts by 14 cells number of the RED membrane utilizing a RED self-made laboratory scale. The power density was enhanced by raising the flow rate (0.10 L/min), concentration difference (40 g/L), and the presence of electrode rinse solution. Further, the ion type (monovalent, divalent, and multivalent) influenced the resulting RED power density, where the divalent ion (MgSO4) 's power density was greater than that of the monovalent ion (NaCl). The resistance and selectivity of the membrane were the major keys for the power generation of RED

The world alone cannot thrive and relies on energy production and expenditure. In an ideal scenario, all the energy produced worldwide would be clean and renewable; however, that is not the case. Most developed countries have already taken steps toward a green future, except developing countries that rely heavily on fossil fuels. Determining the costs of transitioning to a purely renewable energy-reliant future is essential for a developing country like the Philippines. One viable source of renewable energy sources is salinity gradient energy. The study aims to identify if salinity gradient energy can be a viable energy source. The researchers selected specific locations across Las Piñas, specifically Zapote and Las Piñas rivers, to show if the subject Location fits the conditions as a source of salinity gradient energy. Using the mathematical model expressed by Hsu et al. (2021), Location A can only generate approximately 0.0005 kWh per cubic meter of saltwater and freshwater mixed. Location B can only generate approximately 0.0004 kWh per cubic meter of saltwater and freshwater mixed. It would take 1000 and 1250 times the amount of fresh water and salt water from Location A and Location B, respectively, to match the energy output calculated by Hsu et al. The amount of energy harnessed from these rivers is insignificant due to its concentration difference. [ABSTRACT FROM AUTHOR]

The power conversion of salinity gradient energy (SGE) between concentrated brine from seawater desalination and seawater by reverse electrodialysis (RED) benefits energy conservation and also dilutes the discharge concentration to relieve the damage to coastal ecosystems. However, two key performance indexes of the maximum net power density and energy conversion efficiency for a RED stack harvesting the energy usually cannot reach the optimal simultaneously. Here, an optimization study on the two indexes was implemented to improve the performance of RED in harvesting the energy. A RED model for capturing the SGE between concentrated brine and seawater was constructed, and the correlation coefficients in the model were experimentally determined. Based on the model, the effects of a single variable (concentration, flow rate, temperature, thickness of the compartment, length of the electrode) on the performance of a RED stack are analyzed. The multi-objective optimization method based on the genetic algorithm was further introduced to obtain the optimal solution set, which could achieve the larger net power density and energy conversion efficiency with coordination. The ranges of optimal feed parameters and stack size were also obtained. The optimal flow velocity of the dilute solution and the concentration of the dilute solution are approximately 7.3 mm/s and 0.4 mol/kg, respectively. [ABSTRACT FROM AUTHOR]

This study investigates the fouling of anion exchange membrane by organic foulants in fresh water, which is one of the causes of performance degradation of reverse electrodialysis (RED). Three organic foulants, namely sodium alginate (SA), humic acid (HA), and sodium dodecylbenzene sulfonate (SDBS) are selected and the behavior of adsorption fouling of the selected organic foulants is monitored, analyzed and identified using physicochemical (ion exchange capacity (IEC), water uptake (WU)) and electrochemical (permselectivity, electrochemical impedance spectroscopy (EIS), j-V and j-P plots) methods. Compared to the pristine membrane, the resistance of anion exchange membrane increases and the selective permeability, IEC, and WU decrease after fouling of the membrane, which in turn affects the RED cell performance. SDBS, an aromatic substance, shows a higher adsorption capacity as compared to the other two foulants, and therefore causes severe degradation. Among the two aliphatic substances, namely, HA and SA, HA exhibited higher adsorption capacity than SA because it has fewer carboxylic groups. To summarize, the degradation behavior of the anion exchange membrane was clearly different based on the characteristics of each organic foulant. [ABSTRACT FROM AUTHOR]

Anion Exchange Membranes (AEMs) are positively charged polymer membrane used in many applications. In RED systems, AEMs could be used to separate ions to produce energy, and on the other hands remove unwanted molecules in wastewater. This study used three masses of colloidal silica (SiO2) as inorganic filler, three mass ratios of polymer mixture (where; PVA as an inert polymer and PDDA as an active polymer) and three different solvents (H2O, DMSO, and DMF), to produce composite AEMs. The properties of fabricated membranes, were measured to be used in the RED systems. RED membranes produced by DMSO showed the best yields where area resistance (AR), swelling degree (SD), and fixed charged density (FCD) were 1.69 k.Ω.cm2, 31.56%, and 0.26 mmol/g H2O, respectively, at the mixed mass ratio φ(PDDA/PVA)/SiO2 of AEM (0.528:0.4; DMSO). SiO2 can create a layer that can strengthen the matrix membrane, formed through -C(=O)-O-C- and -Si-O-Si- bonds. SiO2 can also encourage the formation of quaternary ammonium bonds. The higher the ratio of the mixture used can increase the number of quaternary ammonium bonds to improve AR and permselectivity. The use of water as solvent in the preparation of AEMs from PVA/PDDA/SiO2 mixture is also promising, by produce equivalent ion exchange properties, yet environmentally-safe.

Reverse electrodialysis (RED) is a promising way of harvesting salinity gradient energy (SGE). The seawater or industrial wastewater may have various pHs. Here the RED performance involving sodium salt solutions with different ion valence ratios including anions of Cl-, SO 4 2-, and PO 4 3- is experimentally investigated in symmetric and asymmetric pH configurations. In the symmetrical pH configuration, increasing the solution pH significantly weakens the energy conversion performance for the 1:1 and 1:3 salts; for the 1:2 salt, the power density and energy conversion efficiency increase and then decrease with increasing pH due to the coupling effects of OH- on the ion transportation through AEMs and CEMs. In the asymmetric pH configuration, increasing the pH of the low concentration solution decreases the power density and energy conversion efficiency. As the pH of the high concentration solution increases, the output power and energy conversion efficiency decrease and then increase for the 1:1 salt due to the coupling effects of the ion transmembrane concentration difference and OH- on the ion migration of IEMs; for the 1:2 salt, the output power and energy conversion efficiency increase and then decrease; for the 1:3 salt, OH- inhibits the hydrolysis of Na 3 PO 4 and anion migration, leading to the lowered output power density and energy efficiency. [ABSTRACT FROM AUTHOR]

Innovative technology and methods are crucial for making pure and refreshing water. Two main methods are present to delete soluble salts from water: membrane processes and thermal processes. A beneficial membrane technique is reverse electrodialysis. This research used molecular dynamics (MD) simulation to investigate how channel roughness affected particle diffusion and permeability in carbon nanotubes (CNTs) via the reverse electrodialysis process. The results indicate that adding roughness in the CNT duct increased the force between the primary fluid and the duct. Using an armchair-edged CNT structure maximized the electric current in the sample. Furthermore, the roughness increased the intensity of force in the channel, which was due to gravity, leading to a decrease in the mobility of fluid particles. Additionally, several broken hydrogen bonds inside the simulation box increased from 116 to 128 in the duct sample with roughness. [Display omitted] • Molecular dynamics method was implemented. • Using the carbon nanotube with an armchair edge, the maximum electric current is obtained. • Addition of roughness in the carbon nanotube channel increases the intensity of the force between the base fluid and channel. • Number of broken hydrogen bonds increases from 116 to 128 in the duct sample with roughness. [ABSTRACT FROM AUTHOR]

• Simultaneously produces hydrogen and treats wastewater using low-grade heat; • Higher feed solution concentration boosts energy conversion efficiency; • Increased heat temperature assists salt renewal, yet hampers conversion efficiency; • The peak values for degradation rate and hydrogen generation are 47.1 % and 0.2 kW; • Under optimal conditions, total energy conversion efficiency reaches 1.65%. Air-gap diffusion distillation (AGDD) is a thermal distillation technology that can convert low-grade heat sources into salinity gradient energy, offering broad application potential. Since the AGDD system operates under atmospheric pressure, it can be seamlessly integrated with reverse electrodialysis (RED) technology, facilitating the conversion of low-grade thermal energy into electricity, hydrogen, and chemical energy. This paper constructs, for the first time, an AGDD-RED mathematical model that simultaneously achieves hydrogen generation and wastewater purification. Accordingly, the influence behaviors of the concentration of AGDD feed solution (0.5 mol·L-1-5 mol·L-1) and low-grade heat source temperature (55–95 °C) on hydrogen generation performance and degradation efficiency are simulated and discussed. At a feed concentration of 3 M, hydrogen generation and COD degradation rates achieve their peak values of 0.19 kW and 46.4 %, respectively. At 55 °C, the degradation rate and hydrogen generation reach their highest values, at 47.1 % and 0.2 kW, with the total energy conversion efficiency reaching 1.65 %. Finally, the energy distribution of the entire system is analyzed, and the results show that the salinity gradient energy regeneration process in the AGDD subsystem is the key factor affecting the efficiency of the system. Reducing pump power consumption and non-ohmic resistance in the RED subsystem will effectively improve the energy conversion performance of the system. [ABSTRACT FROM AUTHOR]

In this study, novel pore-filled anion-exchange membranes (PFAEMs) modified with polypyrrole (PPy) and reduced graphene oxide (rGO) were developed to improve the energy harvesting performance of reverse electrodialysis (RED). The surface-modified PFAEMs were fabricated by varying the contents of PPy and rGO through simple spin coating and chemical/thermal treatments. It was confirmed that the PPy and PPy/rGO layers introduced on the membrane surface did not significantly increase the electrical resistance of the membrane and could effectively control surface characteristics, such as structural tightness, hydrophilicity, and electrostatic repulsion. The PPy/rGO-modified PFAEM showed excellent monovalent ion selectivity, more than four times higher than that of the commercial membrane (AMX, Astom Corp., Tokyo, Japan). This means that the PPy/rGO layer can effectively reduce the permeation of multivalent ions with a high charge intensity and a relatively large hydration radius compared to monovalent ions. The results of evaluating the performance of the surface-modified PFAEMs by applying them to a RED cell revealed that the decrease in potential difference occurring in the membrane was reduced by effectively suppressing the uphill transport of multivalent ions. Consequently, the PPy/rGO-modified membrane exhibited a 5.43% higher power density than the AMX membrane.

Problem Statement. Today, humanity is in search of new sources of energy to make the economy more sustainable, as well as the need for a transition to energy that works on the principles of Carbon-Free Technology. For the Black Sea, this is expressed in the desire for successful implementation of the program Blue Growth Accelerator, which is aimed at the introduction of innovative technologies and alternative energy sources in the energy sector of the Black Sea countries, for the development of the "Blue Economy" and the achievement of its healthy, productive and sustainable state. Salinity gradient power (SGP) is one of the new renewable energy sources. The most studied methods for obtaining SGP energy are technologies based on: Reverse Electrodialysis and Pressure Retarded Osmosis. The interaction of fresh and salt water can provide, in fact, unlimited, free and clean energy. The basis for the generation of such energy is the so-called salinity gradient that occurs when two types of water are mixed. After decades of work and numerous experiments, scientists have developed a way to use the energy of the salinity gradient to generate electricity. This type of electricity is also called "Blue Energy" by association with the color of mixing freshwater and salt water when rivers flow into the ocean. Places (estuaries or deltas), where rivers flow into the oceans and seas, have a truly enormous energy potential. The aim of this study is to identify sites in the northwestern Black Sea region with the necessary conditions for the development of Salinity Gradient Power energy, as well as to assess their potential using the example of estimating the maximum theoretical power of the Pressure Retarded Osmosis process. Research Methodology. In a PRO system, the less concentrated solution flows towards the more concentrated solution due to the positive osmotic pressure difference as long as this difference remains greater than the hydrostatic pressure difference. It is by this principle that osmotic power is produced. Theoretically available amount of energy released when mixing 1 m³ of saturated brine (5 mol/l NaCl solution) and 1 m³ of sea water (0.5 mol/l NaCl) at 293 K is 10 MJ. In the northwestern Black Sea region, along the coast between the Danube and Dnieper rivers, there are 21 limans (lagoons) of which some can be used to generate of Salinity Gradient Power. Results. The results of calculating the maximum net power showed that highest values obtained in the summer months, when the salinity in limans reaches its maximum and, consequently, its difference with the salinity of sea (river) water increases. Proceeding from maximum net power, obtained for the Western Sivash, where the salinity is maintained artificially at certain values, it can be seen that the annual amplitude has a smaller value, which provides more stable conditions. There are objects in the northwestern Black Sea region, in the waters of which, as soon as technologies become available, it will be possible to implement SGP projects. The Kuialnyk Liman, Sasyk- Sivash lake and Western Sivash have the most favorable conditions, where the highest power indicators are shown when using the sea water – hypersaline solution scheme, in which freshwater is not consumed. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) is a renewable energy-generating SGE technique using energy from salinity gradients. This research investigates the effect of membrane and feed characteristics on reverse electrodialysis (RED) power generation. Some investigations on the process parameters effect for the complement of the main study were also conducted. The generated power of RED was measured using power density analysis. The experiments were performed using artificial seawater varied from 0 to 1 g/L NaCl for diluted salt water and from 0 to 40 g/L NaCl for concentrated salt water. In a study of ions type, NaCl non-pa is used to represent monovalent ions, and MgSO4 represents divalent ions. The results showed that the highest voltage generation is 2.004 Volts by 14 cells number of the RED membrane utilizing a RED self-made laboratory scale. The power density was enhanced by raising the flow rate (0.10 L/min), concentration difference (40 g/L), and the presence of electrode rinse solution. Further, the ion type (monovalent, divalent, and multivalent) influenced the resulting RED power density, where the divalent ion (MgSO4) 's power density was greater than that of the monovalent ion (NaCl). The resistance and selectivity of the membrane were the major keys for the power generation of RED. [ABSTRACT FROM AUTHOR]

The energy crisis is one of the most emergency problems that humanity is facing now. To alleviate energy crisis, some new energy sources different from traditional fossil energy are developed in the past decades, for example, nuclear energy, wind energy, solar energy, et al. Among these new energy sources, an important energy existing in the ocean and river named as salinity gradient energy benefits from the features of green, safe, low cost and huge amount, and comes into the researcher's sight. In this article, we review the recent progress in harvesting salinity gradient energy with reverse electrodialysis (RED) membrane. First, the mechanism of RED was introduced, including the basic structure and working principle of RED, the ion selectivity, and the ion rectification effect. The materials which are suitable for RED were discussed in detail, such as 1D nanofluidic nanochannels, 2D materials, and composite materials. Among these materials, 2D materials are thought to be one kind of powerful material for RED because of the feasibility of producing ion-selective membranes. Besides, we dwell on the influences of solution conditions on the RED performance, like the salt gradient and species, pH value, and so on. Finally, we discussed what the RED membranes need in theory and experiment to satisfy the practical application. And the large-scale production and the anti-fouling for the long-term running of RED membranes are two key issues needed to be solved through the analysis of this paper. [ABSTRACT FROM AUTHOR]

Summary: Reverse electrodialysis (RED) is a renewable energy production method that employs salinity gradient to produce electricity. The salinity gradient between the rejected brine of desalination process and river water/seawater is a reliable source of energy, particularly for desalination plants located in susceptible areas. In this study, the performance of RED is predicted using computational fluid dynamics and an artificial neural network. This approach reduces the computational costs of optimization, and more importantly, networks can be updated by more data in the future. Since geometric, hydrodynamic, and electrochemical variables affect the performance of these cells, ignoring any of them will influence the final design. We can consider all of these factors through deep learning. Performance parameters such as Sherwood number, Power number, and concentration polarization coefficient are evaluated in this study. Mass transport and pressure drop are optimized using genetic algorithm, and accessible electrical power is obtained for the optimized cases that help designers make final decisions. Using predictors and a set of optimized cases provide an efficient tool for the design. Based on our results, RED cells can produce net power density of 2.4 W m−2 by using rejected brine of desalination and river water as the two solutions. In addition, Sherwood number of 80 and Power number of 5248 show a good balance between the amount of mass transfer and pressure drop in RED cells. [ABSTRACT FROM AUTHOR]

The removal of phenol from simulated wastewater by a reverse electrodialysis reactor (REDR) wastewater treatment system is experimentally investigated in independent or synergetic degradation circulation mode under specific conditions. Results demonstrated that the total degradation efficiencies (ηde,tot) and the total chemical oxygen demand (COD) removal efficiencies (ηCOD,tot) in an independent degradative circulation mode were better than those in a synergetic degradative circulation mode. After 2 h of treatment, the ηde,tot of phenol reached 100% and 99.7%, and ηCOD,- tot reached 59.6% and 51.3%, under two circulation modes, respectively. However, the synergistic degradation cycle mode achieved a balance between hydrogen ion production and consumption during the wastewater treatment process. When the synergetic circulation mode was applied, the pH of the wastewater was always maintained at around 3 without the addition of acid, which reduced the wastewater treatment costs. Moreover, the general current efficiency and the energy consumption of REDR in the synergetic degradative circulation mode were 51.1% and 168.8 kWh/kgCOD, respectively, after 2 h. Therefore, the implementation of REDR with a suitable circulation mode and operating conditions offered a viable alternative to achieve a win-win situation for both energy and the environment. [ABSTRACT FROM AUTHOR]

Inorganic material-incorporated cation exchange membranes (CEMs) with improved properties have drawn attention for reverse electrodialysis (RED). This paper deals with improving CEMs properties by incorporating silica–magnetite inorganic materials from natural resources. First, silica and magnetite were extracted from rice husk and iron sand, respectively. CEMs were prepared using the phase inversion method by incorporating various ratios. The results showed that both silica and magnetite were in micron size with yields of 76.6% and 59.2% wt., respectively. The CEMs containing magnetite materials showed higher ion exchange capacity (IEC) and ionic conductivity than PVC membranes. However, they had a greater swelling degree. The presence of silica reduced the swelling degree from 18.38% to 7.15% leading to membrane strengthening. A maximum IEC and conductivity of CEMs of 0.26 meq/g and 0.524 S/cm were obtained for the membrane prepared with a SiO2/Fe3O4 ratio of 0:4, respectively. However, considering all aspects, the addition of a SiO2/Fe3O4 ratio of 1:3 was the most significant for increasing the fixed cation density and conductivity by 27.49% and 2815%, respectively, compared to other ratios. Thus, this SiO2/Fe3O4 ratio (1:3) should be considered for practical implementation. Performance examination using RED confirmed that the PVC/SiO2/Fe3O4 can be used as CEM for power generating and had comparable performance to commercial membrane.

Efficiently utilizing the low-grade heat contributes to improving energy consumption structure and energy utilization efficiency, as well as preventing environmental deterioration. To harvest low-grade heat below 80 °C, advanced adsorption-based osmotic heat engines are constructed, which consist of an adsorption-based desalination module for thermally separating the salt solution into concentrated and diluted streams, and a reverse electrodialysis module for converting produced salinity gradient into electricity. Two different heat recovery configurations are employed to improve the heat-to-electricity performance: one is that the cooling power generated in the evaporator is used to cool the condenser and the other is that evaporator is coupled inside the condenser. The transient responses are analyzed and the effects of adsorption/desorption time, switching time, working concentration and heat source temperature on the heat-to-electricity performance are discussed. The efficiency with respect to Carnot efficiency is also presented to provide information on effectively utilized level of the available exergy. Compared with original configuration, the reduced effective condensing temperature in Configuration I and the pressurization effect in Configuration II significantly elevate the working capacity, thus to boost the work extracted. At lower working concentrations and adsorption times, the electric efficiency can be improved via Configuration II, while at higher working concentrations and adsorption times, the advanced configurations hinder the electrical efficiency. In Configuration II, compared with original configuration, the electric power and efficiency are improved by 68.3% and 15.2%, respectively, at a heat source temperature of 333.15 K with 2 mol/kg NaCl solution. While with 7 mol/kg NaCl solution, the electric power is augmented by 11.8% while the electric efficiency is decreased by 19.8%. This study may contribute to designing advanced adsorption-based osmotic heat engines to achieve an upgraded heat-to-electricity performance.

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This article mainly reviews the preparation methods of ion exchange membranes for electricity generation by reverse electrodialysis. It is reported that under different preparation methods, the obtained ion exchange membranes have different advantages and are suitable for the research status of different working conditions. The application of ion membranes with different properties in RED was analyzed, and the output power of commercial membranes and tailor-made membranes in reverse electrodialysis power generation systems were compared. The ion exchange membrane has high performance such as low membrane resistance, high ion permeation selectivity, and antifouling, which can significantly increase the output power of reverse electrodialysis. The ion exchange membrane plays a decisive role in the output power of the reverse electrodialysis power generation system. The preparation methods of high-performance ion exchange membranes are studied in order to promote the research and further development of ion exchange membrane preparation technology. [ABSTRACT FROM AUTHOR]

Salinity gradient energy generated by the contact between seawater and river water is one of the promising renewable energies. In the reverse electrodialysis (RED), salinity gradient energy is directly translated into the electricity. The representative problem is a large electrical resistance of river water or dilute solutions. The dilute solutions are poor electrically conductive. This results in a huge energy loss when an electrical current passes through it.In this study, sodium chloride (NaCl) or poly(sodium 4-styrenesulfonate) (NaPSS) was added to the dilute solutions to increase the conductivities and enhance the power outputs of the RED cells. When NaCl was added, the power output reached 11.4 ± 0.6 µW. On the other hand, when NaPSS was added, the power output increased up to 19.6 ± 0.6 µW.

[Display omitted] Electrodialysis (ED) uses electric energy to conduct the desalination, while bipolar membrane reverse electrodialysis (BMRED) converts the chemical energy containing in acids and alkalis into electric energy. Here, a novel membrane stack (BMRED-ED) based on BMRED and ED was designed to realize the simultaneous energy self-sufficient desalination and energy output process. The stack was studied in two different operation modes systematically. Results of the open-loop operation mode demonstrate that the maximum power density (P d , max ) can obtain a highest value of 4.53 W·m−2, and the maximal average apparent permeability (α) between the open circuit voltage (OCV) and theoretical electromotive force (EMF) is 92.23 %. Results of the closed-loop operation mode indicate that the final desalination ratio (ξ del ) can attain as high as 89.57 %, and the corresponding energy utilization ratios of the desalination (η des ) and the energy output (η out ) are 0.90 % and 14.00 %, respectively. Moreover, the effect of desalinated salt solution concentrations and discharging current densities on the closed-loop operation performance are much more remarkable than that of cation species in the alkali and salt solutions. This work provides a feasible and competitive strategy for simultaneous energy self-sufficient desalination and energy output. [ABSTRACT FROM AUTHOR]