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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]

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]

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]

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 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]

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.

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]

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]

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]

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]

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]

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]

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 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]

• Temperature difference of solutions has a crucial effect on the reverse electrodialysis process. • The enhancement effect is more pronounced under negative temperature difference (NTD) mode. • The highest H 2 production of 1.128 ± 0.019 mol∙m−2∙h−1 is achieved under NTD mode at 25℃. • Performances of the system using three kinds of solutions with different thermal effects are studied. • Effects of cations and anions on the power density and hydrogen productivity were tested out. Reverse electrodialysis (RED) is an emerging technology that converts the salinity gradient energy (SGE) embedded in two solutions of different concentrations into electricity or hydrogen productivity. Given that two solutions containing SGE in nature are often at different temperatures, this study experimentally investigated the effects of the temperature and salinity ratio of the working solutions on the performance of RED systems. The results show that the power density and hydrogen productivity of RED systems could be markedly improved by adjusting the imposed temperature difference on the basis of the salinity gradient. The degree of improvement mainly depends on the magnitude and direction of the temperature difference between the high- and low-concentration solutions. The enhancement effect was more pronounced under a negative temperature difference (NTD) than under a positive temperature difference (PTD). Additionally, the improvement in system performance owing to the temperature difference was not affected by the endothermic or exothermic effects of different solutes in the water. At a NTD of 25℃ and a concentration of 0.1 M aqueous NaOH as the electrode solution, a RED system based on LiBr solution with a salinity ratio of 4.5 M/0.02 M as the working solution achieved a maximum power density of 0.754 ± 0.006 W∙m−2 and the highest hydrogen productivity of 1.128 ± 0.019 mol∙m−2∙h−1, which was 15.1% and 5.5% higher than the hydrogen productivity under LiCl and NaCl solution conditions, respectively. These results show the great potential of LiBr solution in the field of RED hydrogen productivity. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) generates electric energy converted from salinity gradient by using membranes. As the lower concentration results in current loss by ionic resistance, multi-ionic RED has been proposed to enhance RED performance. This study focused on a complete description of ionic transport behavior in the multi-ionic RED. Analytical models for the entire membrane active area were constructed in three-dimensional Multiphysics using fluid dynamics and Nernst-Planck framework. To effectively estimate multi-ion transport and device performance, a calibration for the diffusion coefficient, which is an inaccessible parameter in the membrane region, was progressed and validated with experimental data. Open circuit voltage and short circuit current tracked the diffusion coefficient in relation to the volumetric flow rate of the electrolytes. By incorporating an additional regression analysis model for calibration, the performance of the geometrically modified devices for membrane active area, electrolyte thickness, and flow mode of the electrolyte was predicted and also verified for membrane active area. This method facilitates accurate multi-ionic transport analysis with simplified computation and a complete reflection of numerous factors in the diffusion coefficient. Our predictive tools were consequently applied to design a highly efficient RED device with complex ion composition and optimize the operating fluid conditions. [Display omitted] • A prediction model for monovalent selective RED was developed. • Monovalent selectivity of the membrane was specified by calibration of diffusion coefficient within membrane region. • For regression model of the calibration, maximum mean bias error corresponds to 5.7 %. • Power generation of a geometrically modified double-Donnan RED device was investigated using the developed engineering tools. [ABSTRACT FROM AUTHOR]

• The P max of 3.74 W/cp m−2 was achieved with a temperature gradient of 60⁰C:25⁰C. • A maximum efficiency of 24% was obtained for a RED stack operating with only NaCl. • Between 25⁰C- 60⁰C, SO42- and Ca2+ reduced the permselectivity of IEMs. • Divalent ions, SO42- and Ca2+ increased the electrical resistance of IEMs. Hydraulic fracturing (HF) wastewaters have high salinities relative to feed waters and can be an economic and environmental burden. However, salinity differences between these two solutions offer the opportunity for electricity generation using reverse electrodialysis (RED) stacks. HF wastewaters are much hotter than feed waters, but the relative impact of temperature for RED has been relatively unexplored. We investigated power generation using HF fluids in RED stacks, focusing on the impact of temperature differences between feed and wastewater. Power from synthetic solutions (mixtures of NaCl, Na 2 SO 4 , and CaCl 2) produced up to 0.96 W/cp m2 when both solutions were 25 °C and increased to 1.51 W/cp m2 when both solutions were at 60 °C. With an actual HF wastewater power production was 1.27 W/cp m2 at 25 °C with no temperature difference, and 3.74 W/cp m2 with a 25 °C feed solution and 60 °C HF wastewater. Comparing synthetic and HF wastewaters showed that the presence of sulfate and calcium ions reduced permselectivity and increased the electrical resistance of the membranes. Increasing the temperature, however, reduced electrical resistances. A thermodynamic model using Gibbs energies, and short- and long-range interactions of ions/ion-water was used to assess energy efficiency. The overall energy efficiency of the RED stack, based on ion concentrations in the inlet/outlet streams, was 24 % using NaCl at 50 °C. These results show that electricity can be effectively generated using salinity differences of HF streams and highlight the additional benefits of using solutions with different temperatures. [ABSTRACT FROM AUTHOR]

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]

Reverse electrodialysis (RED) is an eco‐friendly power generation system that produces electricity from the salinity difference between two solutions of different concentrations. Recently, research on RED has expanded not only to increase the maximum power density, but also to converge with other energy generation systems. Most importantly, miniaturized RED has been developed rooted on its nature, such as convenient customization and electrodeless character. This RED, being compact and readily disposed, functions as a unique type of power source, operating solely by the flow of ions, which is thus perfectly compatible to integrate with various bio‐related systems. We emphasize the potential of this RED as a hybrid, disposable, portable and fully ionic power source and look forward to its wide range of application scopes in the future. [ABSTRACT FROM AUTHOR]

During the traditional reverse electrodialysis (RED) process, second only to concentration polarization phenomenon, the spacer shadow effect that blocks the ionic transport as a consequence of the use of non-permselective spacers has an undesirable impact on the practical power output. In this work, a configuration of ion-permselective spacer is proposed to eliminate the spacer shadow effect to improve the power density. By combining direct current and alternating current experimental methods, the spacer shadow and concentration polarization effects are measured. At the same time, their impact on stack resistance and power out are analyzed quantatively under different hydrodynamic conditions and spacer configurations to optimize the RED process performance. Compared with traditional spacers, the use of ion-permselective spacers makes the spacer shadow effect reduced by more than 95% inversely with a stronger concentration polarization phenomenon, which results in a higher power density due to remarkable decrease in stack resistance. In order to further suppress the concentration polarization, increasing flow rate and reducing pore size of channel are both feasible, which meanwhile leads to a further reduction in shadow effect. Yet, the variation of channel shape has little impact on the shadow and concentration polarization effects. The maximum power output of 0.81 W/m2 is harvested with pore size of 4.5 mm and cell pair of 3 at flow rate of 40 L/h under the investigated conditions and is improved by 50% in comparison to non-permselective spacers. [ABSTRACT FROM AUTHOR]

Solution pH can impact the nanochannel surface charge density, thus, to regulate the transmembrane ion transportation. Here, the performance of nanofluidic salinity gradient energy conversion is investigated, where the solution pH at the high/low concentration side varies separately, rendering asymmetric pH configurations. Results reveal that the solution pH at the low concentration side (pH L) exhibits a significant impact on the salinity gradient energy conversion. When pH L < Isoelectric Point (IEP), the energy conversion indicators are most stable under various solution pH at the high concentration side (pH H). The surface charge density of the nanochannel at the low concentration end determines the transmembrane ion transportation characteristics, dominating the energy conversion performance. The energy conversion performance via nanochannels of different lengths under asymmetric pH configurations is also studied. There exists optimal nanochannel length corresponding to the maximum electric power, which differs under various pH configurations. For longer nanochannels, the ion concentration polarization effect is weakened, allowing for a more effective energy extraction performance via pH-adjusted salinity gradients. At the length of 2000 nm, the electric power and energy conversion efficiency under the co-direction configuration is 78% and 97.9%, respectively, larger than those under the reverse direction configuration. [ABSTRACT FROM AUTHOR]

This study is the first comprehensive life cycle assessment (LCA) of reverse electrodialysis (RED), a technology that converts salinity gradient energy into electricity. Our goal is to identify RED system components of environmental concern and provide insights on potential environmental impacts. We conduct an attributional LCA of two RED scenarios: large‐scale energy generation from natural bodies of water and smaller‐scale energy generation from industrial processes. A functional unit of 1 MWh of net electricity production enables comparison to existing renewable energy technologies, including wind and solar photovoltaics. Under theoretical, favorable conditions, environmental impacts from RED are found to be comparable to, and often lower than, established renewable energy technologies. Processes associated with membrane manufacture are primary contributors to six of the nine evaluated impact categories. Under baseline assumptions, impacts are an average of 50% higher for the Natural Water scenario compared to the Concentrated Brine scenario because of the increased power density achieved with concentrated brines. This early‐stage LCA demonstrates that the expected environmental impacts of RED are comparable to existing renewable technologies and a large improvement over fossil‐based generation. However, eutrophication, ecotoxicity, and carcinogenic impacts are larger for RED than other technologies under some assumptions. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis is a promising membrane technology to generate energy from controlled mixing of water streams of different salinities. Electrical potentials generate on the ion exchange membranes (IEMs) when selective transport of cations and anions across the membranes driven by concentration difference. The accurate determination of the potentials developed on the IEMs is critical to fairly assess the feasibility of the technology. The Nernst-Planck-Poisson (NPP) equations for IEMs (the membranes with fixed charge) were solved numerically with the boundary updating scheme. The validity of this numerical method was verified by the identical values of Donnan potential obtained with the well-established analytical methods. The suitability and applicability of the classic Teorell-Meyer-Siever (TMS) model were assessed by comparison to the simulation results from the numerical method. [ABSTRACT FROM AUTHOR]

Electrodialysis, especially reverse, is a promising method of water desalination, concentration of solutions, extraction of valuable components from waste and rinse water, and power generation. The main problem is the search for low-cost universal anode-cathode materials. The work aims to determine the possibility of using the VNZh90 superalloy (5 % Ni, 5 % Fe, 90 % W) and the electroplated Ni-W alloy as a universal cathode-anode material for reverse electrodialysis. The crystal structure of the Ni-W alloy was studied by X-ray diffraction analysis; the morphology was studied by scanning electron microscopy. The anodic behavior of both alloys was studied by voltammetry in 6 % HCl in a saturated NaCl solution. The high passivity of the VNZh90 superalloy was revealed. On the repeated anodic curve, the current density of the passivation plateau decreased 2.8 times and was 37 mA/dm². This indicates that the use of the VNZh90 superalloy is promising as a universal cathode-anode material of a reverse electrodialyzer. The phenomenon of significant passivation for the Ni-W alloy was also revealed. The primary curve of the alloy showed two dissolution peaks and a well-defined passivation plateau. Probably, the first peak corresponded to a more active phase with a low W content. This was confirmed by the absence of the first peak on the repeated anodic curve and the identity of the passivation plateaus of the primary and repeated curves. The passivation current density was 209 mA/dm². These data also indicate the possibility and prospects of using the electroplated Ni-W alloy as a universal cathode-anode material of a reverse electrodialyzer after optimizing the composition and deposition method of the alloy, as well as reducing the wear rate. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel integrated system of carbon dioxide absorption and RED was operated. • Capacities of MEA, DEA, and MDEA were 0.93, 0.83, and 0.69 mol/mol respectively. • Power density of MEA, DEA, and MDEA were 0.75 0.58, and 0.41 W/m2 respectively. • The high power density of MEA and DEA is due to carbamate formation. • MDEA absorbent showed excellent regeneration efficiency of over 99%. In this study, the performance of a novel integrated carbon dioxide (CO 2) capture and reverse electrodialysis (RED) system was evaluated. The optimal operating conditions and carbon dioxide absorption and desorption mechanisms were identified. The proposed system utilizes a RED device to recover energy from the desorption step of the CO 2 capture process, which is known to have high energy requirements in conventional processes. It has the potential as a hybrid process capable of recovering absorbent, energy, and bicarbonate through RED. To verify the performance of the system, CO 2 loading, power density, and absorbent regeneration were evaluated using primary (monoethanolamine, MEA), secondary (diethanolamine, DEA), and tertiary (N-methyldiethanolamine, MDEA) amines. In the case of primary and secondary amines, carbamates, intermediate products, are formed and pass through the ion exchange membrane of RED, thereby achieving high power density. However, they are re-substituted with amines after passing through the ion exchange membrane (IEM), leading to the loss of absorbent. Conversely, in the case of tertiary amines, no intermediate products were formed, and excellent absorbent regeneration performance of more than 99.9% was demonstrated through multi-stage RED. Through this, the feasibility of future applications of this technology was confirmed. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) is a promising method for harvesting the salinity gradient energy (SGE) between the brine and river water. Many investigations are carried out by using the artificially brine and fresh water, bringing difficulties in reflecting the practical RED performance under the complex influences of feed solutions. This work explores the performance of the RED system for hydrogen and electricity co-generation that is driven by salinity gradient between the actual concentrated brine and natural river water, and compared with the simulative brines and river waters under six testing schemes. The results show both the working current and solutions influence the system performances, including the output voltage, power density, hydrogen production, and energy conversion efficiency. Besides, the effects of salinity gradient of feed solutions are greater than that of the presence of trace multivalent ions and anionic radical in brine. The effective monovalent ion ionic strength is vital. The experimental maximum hydrogen production and power density are 82.12 mL·h−1 and 0.124 W·m−2 respectively at the current is 0.2 A, and the total power reached 0.32 W with the energy conversion efficiency of 25%. The research offers recommendations for harnessing SGE from actual brines and freshwater to produce hydrogen. • An innovative process of energy recovery from the actual brines and freshwater was presented. • A reverse electrodialysis stack was built to produce H 2 driven by actual brine and river water. • Feasibility is analyzed based on the comparation testes by 3 brines and 3 fresh waters schemes. • Maintaining a suitable working current heightens H 2 production and total power output. • Power density is 0.149 W·m−2 and H 2 production is 82.12 ml·h−1, at the current is 0.2 A. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new strategy termed selective reverse electrodialysis (SRED) was proposed. • SRED was utilized to recover salinity gradient energy (SGE) from salt-lake brines. • SRED was comprehensively compared with the conventional RED (CRED). • The role of Mg2+ in the brines on the adverse effects in SRED was regulated. • Recovering SEG from salt-lake brines can make effective supplements for energy. The salinity gradient energy (SGE) in salt-lake brines can be exploited as a sustainable energy source through reverse electrodialysis (RED). However, the composition of brines is notably intricate. In order to avoid the adverse effects of multivalent cations on RED in brines, we introduced a novel selective reverse electrodialysis (SRED) here. The results demonstrate that when increasing the salinity ratio between high and low concentration feeds (HCFs, LCFs) from 20 to 60, the SRED maximal maximum power density (P d, max) improves from 0.069 to 0.109 W/m2. The feed salinity has less obvious effect on SRED. Moreover, the role of Mg2+ on the adverse effects is regulated. The maximal P d, max of SRED is 1.13 ∼ 1.23 times higher than that of the conventional RED at the Mg2+ concentrations of 4861.00 ∼ 14583.00 ppm in HCFs and 40.51 ∼ 121.53 ppm in LCFs. This suggests that SRED is a feasible and efficient strategy for capturing SGE in salt-lake brines. [ABSTRACT FROM AUTHOR]

In this study, the possibility of preparing fresh water through environmental friendly process of hybrid electrodialysis (ED)-reverse electrodialysis (RED) has been investigated. Therefore, the process performance has been evaluated with regard to both desalination and energy generation. Besides, the process has been modeled with real and synthetic concentrated brine with high salinity of up to 200,000 ppm from Persian Gulf seawater and synthetic and real brackish water with the salinity of up to 7,240 ppm from rivers in Bushehr province, Iran. Results demonstrated that the RED system was capable of generating the energy needed to desalinate brackish water with the salinity of less than 1,000 ppm, while for higher salinities, an extra amount of electrical energy is required. It was also revealed that the best desalination performance (salt removal percentage) for brackish water with initial concentration of 1,000; 2,000 and 4,000 ppm was 42%, 53% and 52%, respectively. Moreover, due to high level of salinity along with the presence of a variety of minerals in river waters, the rate of electricity production and desalination was less than that of the synthetic water samples on a pilot scale; for example, for the Mond River with an initial salinity of 2,690 ppm, the salinity reduction was around 27.17%. [ABSTRACT FROM AUTHOR]

As wearable technologies redefine the way people exchange information, receive entertainment, and monitor health, the development of sustainable power sources that capture energy from the user's everyday activities garners increasing interest. Electric fishes, such as the electric eel and the torpedo ray, provide inspiration for such a power source with their ability to generate massive discharges of electricity solely from the metabolic processes within their bodies. Inspired by their example, the device presented in this work harnesses electric power from ion gradients established by capturing the carbon dioxide (CO2) from human breath. Upon localized exposure to CO2, this novel adaptation of reverse electrodialysis chemically generates ion gradients from a single initial solution uniformly distributed throughout the device instead of requiring the active circulation of two different external solutions. A thorough analysis of the relationship between electrical output and the concentration of carbon capture agent (monoethanolamine, MEA), the amount of CO2 captured, and the device geometry informs device design. The prototype device presented here harvests enough energy from a breath‐generated ion gradient to power small electronic devices, such as a light‐emitting diode (LED). [ABSTRACT FROM AUTHOR]

Perchlorate (ClO4) is a toxic anion that inhibits iodine uptake by the thyroid gland and subsequently disrupts thyroid hormone production. In this study, the feasibility of using reverse electrodialysis (RED) was examined for the treatment of perchlorate in salt (5% NaCl; w/v) water. RED uses direct electricity, produced by salinity gradients in a membrane stack, to drive the electrochemical treatment of wastewater. Operational conditions such as salinity gradient (S.G.), number of membrane pairs, and stack solution flowrates were varied and their effects on electricity generation and perchlorate reduction were investigated. Experimental batch results showed that a higher number of membrane pairs and salinity gradient gave higher values of power density, which also resulted in higher abatement of perchlorate. In contrast, the reduction of perchlorate was lowered upon increasing the stack solution flowrate. The maximum abatement of perchlorate (38.76%) was achieved using 15 pairs of cation and anion exchange membranes and 5 M/0.005 M salinity ratio (S.G. 1,000) of high and low concentrated NaCl solutions at 1.5 mL/min stack solution flowrate. This study successfully demonstrated that RED can be a sustainable alternative method for the abatement of perchlorate in salt waters. [ABSTRACT FROM AUTHOR]–) is a toxic anion that inhibits iodine uptake by the thyroid gland and subsequently disrupts thyroid hormone production. In this study, the feasibility of using reverse electrodialysis (RED) was examined for the treatment of perchlorate in salt (5% NaCl; w/v) water. RED uses direct electricity, produced by salinity gradients in a membrane stack, to drive the electrochemical treatment of wastewater. Operational conditions such as salinity gradient (S.G.), number of membrane pairs, and stack solution flowrates were varied and their effects on electricity generation and perchlorate reduction were investigated. Experimental batch results showed that a higher number of membrane pairs and salinity gradient gave higher values of power density, which also resulted in higher abatement of perchlorate. In contrast, the reduction of perchlorate was lowered upon increasing the stack solution flowrate. The maximum abatement of perchlorate (38.76%) was achieved using 15 pairs of cation and anion exchange membranes and 5 M/0.005 M salinity ratio (S.G. 1,000) of high and low concentrated NaCl solutions at 1.5 mL/min stack solution flowrate. This study successfully demonstrated that RED can be a sustainable alternative method for the abatement of perchlorate in salt waters. [ABSTRACT FROM AUTHOR]

[Display omitted] The deterioration of the environmental situation has led to the need to restructure the world's power industry, and clean renewable power sources are coming to the forefront. This review deals with recent advances in the development of promising ion-exchange membrane materials for two types of application that have been intensely developing recently, namely, hydrogen energy and reverse electrodialysis. Special attention is paid to the comparison of two properties of membranes, conductivity and selectivity, that are competing but fundamentally important in both areas. Perfluorinated sulfonic acid membranes now play a dominant role in hydrogen power engineering, as they provide not only high proton conductivity but also chemical stability and low gas permeability. The review also covers other types of membrane materials, including anion exchange membranes, polybenzimidazoles and hybrid membranes containing inorganic nanoparticles that have been actively developed in recent years. The milder operating conditions of membranes in reverse electrodialysis units allow one to use less expensive non-perfluorinated membranes, including grafted ones. It is of note that in devices of this type, the selectivity of membranes to the transfer of oppositely charged ions is a more important parameter. [ABSTRACT FROM AUTHOR]

Solar‐driven interfacial evaporation by localization of solar heating at the air–liquid surface has emerged as a cost‐effective desalination technology. The rapid interfacial evaporation induces simultaneous salinity and temperature gradient between evaporation surface and bulk water, which enables electricity generation but is not comprehensively utilized. Herein, the combination of a thermogalvanic cell (TGC) and reverse electrodialysis (RED) in solar‐driven interfacial evaporation is proposed to extract energy from temperature and salinity gradients simultaneously. Because of the synergistic ion transport effect, the coupling of TGC and RED enables mutual power enhancement by orders of magnitude based on the rational spatial layout and the fabrication of composite electrodes. Finally, a steam‐electricity cogeneration system is designed, which achieves the 1.4 kg m−2 h−1 vapor and 1.11 W m−2 electricity simultaneously under one sun illumination. This concept opens a promising avenue towards a solar‐driven water‐energy nexus. [ABSTRACT FROM AUTHOR]

Summary: Fossil fuel is scanty and negatively affects the earth by inducing climate change. As a result, alternative and renewable energy (RE) sources are being investigated to replace fossil fuel. Wind and solar energy are leaders in the RE market, but huge and accessible other energy sources such as salinity gradient power (SGP) exist and need to be collected to contribute to the global energy demand. SGP is mainly extracted with reverse electrodialysis (RED) and pressure retarded osmosis (PRO) systems. The applicability of RED‐SGP in a natural environment is the current challenge due to the low power density and the high Levelized cost of energy (LCOE) of the process. The properties of the ion‐exchange membranes (IEMs), the spacers, the feed solutions characteristics and salinity, and the electrodes are among the most important parameters that control the performance of RED‐SGP processes. New highly selective, conductive, and cost‐effective membranes are required to improve RED performance and reduce the produced energy cost. Alternatives feed solutions such as wastewaters and brine from desalination plants as well as hybrid RED such as RED combined to electrodialysis (ED), reverse osmosis (RO), or membrane distillation (MD) will result in cost‐effective water treatment and SGP extraction. [ABSTRACT FROM AUTHOR]

Summary: Steam power plants release more than half of the primary energy input as ultra low temperature heat below 40∘C into the environment causing thermal pollution. The emitted heat has a very low exergy content making it challenging to use as heat input by another process. Adsorption desalination combined with reverse electrodialysis can be powered by this heat and convert it into electricity. Thus, the system can mitigate thermal pollution and generate electricity at the same time. This study combines a validated reverse electrodialysis model with a dynamic adsorption desalination model that is validated with experimental data within this work. The experiments were conducted using a small‐scale adsorption desalinator and silica gel proving the feasibility of the regeneration at heat source temperatures as low as 40∘C. The simulations of the integrated system analyse different heat integration scenarios showing exergy efficiencies up to 15% and energy efficiencies up to 0.55%. Hence, the system could generate 65 kW electricity from a 20 MW heat source considering pumping losses. [ABSTRACT FROM AUTHOR]

Power productions from electrochemical devices are becoming a necessity for decarbonization of the global energy system and can act as a potential candidate for achieving the universal demand for basic energy access. Quenching the high-efficiency are desired with the low-cost device and without emission of harmful greenhouse gasses is the primary purpose of this manuscript. Here we have demonstrated novel nanocomposite membrane, implemented in reverse electrodialysis systems for generating power. The selectivity, compatibility, availability, and flexibility of appropriate spacer and Nafion nanocomposite with the FAA-3 based anion-exchange membrane is outstanding and explained in great detail. Just by altering the nanochannel using micron length single-wall carbon nanotube (SWCNT), the nanocomposite membrane shows stable device performance without accumulation of salt at the Nafion nanocomposite membrane end. Structural and durability of the membrane at high temperatures under-hydrated condition can withstand freely moreover offers remarkable results. We achieve superior performance of the reverse electrodialysis devices without altering device architecture. Modified membrane with commercial available FAA-3 membrane act as a novel membrane for reverse electrodialysis. • A unique combination of Nafion nanocomposite/FAA-3 based IEM's for RED. • Molecular dynamic simulation of prepared nanocomposite membrane. • Reducing fouling of membrane for reverse electrodialysis systems. • Restricting salt accumulation at the FAA-3 membrane in RED cell. • Green and clean energy from open electrochemical cells for power generation. [ABSTRACT FROM AUTHOR]

Solid-state nanopores have shown great potential in investigating salinity gradient energy generation as a renewable power generator. In this work, various diameter silicon nitride (Si3N 4) nanopores were fabricated to investigate the power generation between two potassium chloride solutions with different concentration gradient ratios by reverse electrodialysis. The maximal estimated power density of a Si3N4 nanopore measured experimentally can be high to 16 649Wm − 2 . To compare with the single Si3N4 nanopore, multiple nanopores array has also been investigated. The equivalent circuit model of multiple Si3N4 nanopores array generator is quantitatively constructed by massive reproducible experimental data and theoretical derivation. For nanopore array, the osmotic current basically keep a linear growth with the number of the nanopores at every concentration ratio. While, the osmotic voltage is basically independent on the number of nanopore. The power generation circuit of the nanopore array can be regarded as a parallel circuit of multiple nanopores. Power generation from concentration gradients in Si3N4 nanopores could be widely used in a variety of applications like ultra-low power devices and micro-nano electromechanical systems. Salinity gradient energy was obtained by reverse electrodialysis in silicon nitride nanopores. The maximal estimated power density of single Si3N4 nanopore measured experimentally can be high to 16649 Wm–2. The equivalent circuit model of multiple Si3N4 nanopores array generator is quantitatively constructed by massive reproducible experimental data and theoretical derivation. Power generation from concentration gradients in Si3N4 nanopores could be widely used in a variety of applications like ultra-low power devices and micro-nano electromechanical systems. [ABSTRACT FROM AUTHOR]

Blue energy (or salinity gradient energy) is a renewable, carbon-neutral, and continuous electrical energy source that can be obtained via the reverse electrodialysis (RED) technique. The viability of this technology strictly depends on the performance and cost of the ion-exchange membranes (IEMs) that compose the RED units; designing the optimal membrane represents a critical challenge due to the complex relation between the performance, properties, and structure of the membrane. In this work, we present our findings on an electrospun cation-exchange membrane based on polyvinyl chloride (PVC), a strongly acidic cation exchange resin, with sodium dodecyl sulfate (SDS) as an additive. We contrast it with a similar membrane produced with the more conventional casting solution technique. The electrospinning technique provides thinner and more homogeneous membranes than those synthesized via casting. The membranes were characterized using morphological, spectroscopic, and analytical methods. Scanning electron microscopy images depicted an intertwined nanofiber mesh within the membrane. We also synthesized the same electrospun cation exchange membrane without SDS; this membrane presented 63% less swelling, and a significant increase in the fixed charge density (CDfix) (119.6 meq/g) when compared to its casting solution counterpart (34 meq/g). This suggests an enhanced permselectivity, and thus better performance for blue energy generation in RED units. [ABSTRACT FROM AUTHOR]

This study investigated the effects of fly ash loading on the characteristics of polyvinyl chloride (PVC) membranes for reverse electrodialysis (RED). The membranes were prepared by adding different concentrations of fly ash (0.5-2 wt%) to the casting solution. The surface chemistry of the prepared membranes was analyzed using Fourier transform infrared spectroscopy. The swelling degree (SD) was used as an indicator of the membranes' water uptake. Titration using NaOH (0.01 M) was performed to measure the membranes' ion exchange capacity (IEC) and conductivity. The PVC membrane with 2 wt% fly ash demonstrated the highest SD (83.78%), IEC (0.163 meq/g), and conductivity (8.7x10-2 µS/cm). The results show that the presence of fly ash significantly affects the characteristics of PVC membranes for RED. [ABSTRACT FROM AUTHOR]

Summary: Reverse electrodialysis (RED) is the most promising technique based on ion exchange membranes for harvesting salinity gradient energy. In the present study aimed to explore the sensitivity of the RED stack performance, different concentrations of NaCl were prepared and used to simulate the salinity of concentrated seawater and that of river water at 298 K. Some major factors including the repeating unit pairs, the flow velocity and the feeding concentration were investigated. When the positive effect by the increase of open‐circuit voltage is greater than the negative effect caused by the increase of internal resistance, the electrical performance of RED stack is improved, and the maximum power density is increased. On the contrary, the value of maximum power density is decreased. The maximum power density reached its maximum when eight repeating units were used, and the optimum flow velocity was obtained as 0.71 cm/s. At a same concentration gradient of the feed, a lower internal resistance was observed at a higher total salinity, leading to better energy generation performance. [ABSTRACT FROM AUTHOR]

• A single-sided wave-profiled membrane with wavy sub-corrugations is proposed. • The wave membrane channel has more advantages than pillar membrane channels. • The sub-corrugations enhance mass transfer and reduce concentration polarization. • The membrane channel performance can be improved by geometry optimization. Profiled membranes, the membranes with microstructures on one side or two sides, are expected to be a viable alternative to the spacers and enhance the power output of the reverse electrodialysis (RED) process. However, there are some problems for the present single-sided profiled membranes such as flow stagnating and insufficient fluid mixing. As for double-sided profiled membranes, the membrane preparation and exact stack assembling are still difficult. With respect to these problems, a single-sided wave-profiled membrane with wavy sub-corrugations as additional mixing promoters is proposed in this study. Based on the Computational Fluid Dynamics method, the flow and mass transfer characteristics in the wave-profiled membrane channel and several other channels (for purposes of comparison) are simulated. Results show that the single-sided wave-profiled membrane channel has more advantages than the single-sided pillar-profiled membrane channels especially at low Reynolds numbers typically used in RED applications, although its performance is still inferior to that of the double-sided chevron-profiled membrane channel and woven spacer channel. Furthermore, it can be proved that the wavy sub-corrugations can enhance the mass transfer and reduce the concentration polarization, while they have a better influence on the surface where the sub-corrugations are located. [ABSTRACT FROM AUTHOR]

Concentration gradient batteries (CGBs) use electrodialysis and reverse electrodialysis to charge and discharge, respectively. An important factor hindering CGB efficiency is osmosis through ion exchange membranes (IEMs); however, adding an osmotic ballast to the dilute compartment reduces osmosis and improves CGB efficiency. Despite the importance of osmosis in CGB performance, there has been no evaluation of the effects of CGB parameters on performance with and without an osmotic ballast. Accordingly, our goal was to evaluate the effects of selected CGB parameters on various CGB performance metrics to inform future optimization of CGB designs. Results showed ballast addition improved current and round-trip energy efficiency and stabilized CGB performance across multi-cycle operation. However, ballast addition caused lower average (net) power densities due to its impact on IEM stack resistance and solution viscosity. Increasing the flowrate and decreasing the spacer thickness led to decreases in average net power densities. Importantly, the effect of IEM properties on CGB performance varied with ballast addition: low water permeability IEMs had greater and lower round-trip energy efficiencies without and with ballast, respectively, compared to low resistance IEMs. This work informs CGB parameter selection, demonstrates tradeoffs associated with osmotic ballast addition, and shows multi-cycle CGB operation is feasible. • Ballast addition substantially improved CGB current and round-trip energy efficiency • Ballast addition enabled stabilized CGB operation across multiple battery cycles • Thin spacers and high flowrates weakened CGB performance due to high pressure drops • Effects of altering parameters on RED performance do not directly translate to CGBs • Impacts of IEM properties on CGB performance varied with ballast addition [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) heat engine is a novel technology to convert low grade heat into electricity. Through combining the multi-effect distillation (MED) with RED, the so-called MED-RED heat engine has received increasing attention over the recent years. In this paper, a comprehensive theoretical exergy analysis for the MED-RED heat engine has been carried out based on a validated mathematical model. And the influences of relevant operation and design parameters on the exergetic performance of the heat engine were investigated. The results showed that the preheater, condenser and RED unit were main sources of exergy destruction in the heat engine. The total relative exergy destruction of these three components was 59.8% and the exergetic efficiency of the heat engine reached 4.7% under the design condition. Moreover, elevating the temperature of hot water had a negative effect on enhancing the exergetic performance of the heat engine. On the contrary, increasing the concentration of initial brackish solution or the number of effect evaporators in the MED was helpful for improving the exergetic performance of the heat engine. Finally, discussion in terms of improving the exergetic performance of the heat engine was carried out and relevant approaches were presented. • A comprehensive theoretical exergy analysis for the MED-RED heat engine was implemented. • The exergy destruction of each component in the heat engine was investigated. • The preheater, condenser and MSRED are three main sources of exergy destruction within the heat engine. • Influences of relevant operation and design parameters on the exergetic performance of the heat engine were investigated. • Relevant approaches for improving the exergetic performance of the heat engine were carried out and discussed. [ABSTRACT FROM AUTHOR]