Reverse Electrodialysis Stack Research Articles

Simulation of a Reverse Electrodialysis–Absorption Refrigeration Integration System for the Efficient Recovery of Low-Grade Waste Heat

The absorption refrigeration system (ARS) stands as a remarkable device that is capable of efficiently harnessing low-grade thermal energy and converting it into cooling capacity. The reverse electrodialysis (RED) system harvests the salinity gradient energy embedded in two solutions of different concentrations into electricity. An innovative RED–ARS integration system is proposed that outputs cooling capacity and electric energy, driven by waste heat. In this study, a comprehensive mathematical simulation model of a RED–ARS integration system was established, and an aqueous lithium bromide solution was selected as the working solution. Based on this model, the authors simulated and analyzed the impact of various factors on system performance, including the heat source temperature (90 °C to 130 °C), concentrated solution concentration (3 mol∙L⁻1 to 9 mol∙L⁻1), dilute solution concentration (0.002 mol∙L⁻1 to 0.5 mol∙L⁻1), condensing temperature of the dilute solution (50 °C to 70 °C), solution temperature (30 °C to 60 °C) and flow rate (0.4 cm∙s⁻1 to 1.3 cm∙s⁻1) in the RED stacks, as well as the number of RED stacks. The findings revealed the maximum output power of 934 W, a coefficient of performance (COP) of 0.75, and overall energy efficiency of 33%.

Harnessing salinity gradient energy: Pushing forward in water reclamation via on-site reverse electrodialysis technology

Effluents from urban wastewater treatment plants (UWWTPs) discharged into water bodies such as the sea or ocean, offer a potential source of renewable energy through the salinity gradient (SGE) between seawater and treated water. The European project Life-3E: Environment-Energy-Economy aims to demonstrate an innovative process integrating renewable energy production with water reclamation. Using reverse electrodialysis (RED) technology, SGE can power tertiary wastewater treatment processes in coastal UWWTPs, offsetting energy costs associated with water regeneration and reuse.This study pioneers a pilot-scale RED system with a 20.125 m2 membrane area at a coastal UWWTP in Comillas, Spain. The initial tests with synthetic solutions in the up-scaled RED module have reached a peak power density of 1.39 W/m2. Under real environmental conditions, using natural seawater and treated water at ambient temperatures (289 ± 0.5 K), the system achieved a peak power density of 0.95 W/m2, outperforming previous setups in stability and efficiency.The results show competitive energy metrics, with an energy efficiency of 1.9 W/m2·m³LC and up to 38.2 Wh/m³LC generated. The treated water, with an inlet conductivity to the RED stack of <1 mS/cm, exits the pilot with a conductivity of around 4 mS/cm (measured under a load of 2A and a flow rate of 500 L/h), maintaining the quality standards for urban reuse.This study demonstrates the effective integration of RED technology into water reclamation stages, creating a self-sustained energy loop and enhancing the efficiency in water management. By harnessing blue energy and supporting sustainable water reuse, this research contributes to the global shift toward a circular water economy and critical sustainability goals.

The high energetic potential of hydraulic fracturing wastewaters with both salinity and temperature gradients for electricity generation using a reverse electrodialysis stack

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, Na2SO4, and CaCl2) 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.

A Maxwell–Stefan Approach to Ion and Water Transport in a Reverse Electrodialysis Stack

A Maxwell–Stefan Approach to Ion and Water Transport in a Reverse Electrodialysis Stack

Improved Power Production in Reverse Electrodialysis Stacks with Ion‐Permselective Woven Net Spacers

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.

Green hydrogen production via reverse electrodialysis and assisted reverse electrodialysis electrolyser: Experimental analysis and preliminary economic assessment

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 (REDSC), 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−1H2 was found, thus leaving room for further studies.

Valorization of abandoned mine wastewater for the production of energy in a reverse electrodialysis cell

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.

Assessment of Data Capture Conditions Effect on Reverse Electrodialysis Process Using a DC Electronic Load

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.

Design strategy of cathodic electrocatalysts to effectively suppress inorganic fouling for long-term stability of reverse electrodialysis

In seawater based-electrochemical devices including reverse electrodialysis (RED) and electrolysis devices, inorganic fouling occurs from the cathodic reaction owing to the precipitation of hydroxides and/or carbonates. Inorganic fouling decreases electrocatalytic activity and disrupts the charge transport, thus reducing power density. In this study, we investigated inorganic fouling over various cathodic electrocatalysts prepared for large-scale RED. Notably, nano-Pt/C which has four times higher scaling control than bulk Pt, exhibited a formation of thin and porous foam-like Mg(OH)2, whereas bulk Pt was coated by a thick and dense film-like precipitate. Surface-modified carbon nanostructures showed a stronger anti-fouling behavior than Pt catalysts at high voltages (≥300-cell-paired RED stacks). In particular, acid–air plasma-treated O-rich functionalized C catalysts produced one-dimensional nanostructures, exhibited excellent electrocatalytic activity and allowed rapid charge transport, resulting in a stable RED performance at a power density of 545 ± 1 W m−2 (current density of 35.17 ± 0.02 A/m−2 over 12-h of operation. This study will promote the upscaling of RED systems toward industrial applications that use natural seawater.

Reverse electrodialysis characteristic of the LiBr-ethanol-water ternary solution

Reverse electrodialysis heat engine (REDHE) has a large potential to convert low-grade heat into electrical energy. Working fluids with low distillation temperature and excellent ion migration properties are essential for the performance improvement of the REDHE. Here, we propose an ethanol-assisted LiBr aqueous to simultaneously decrease the distillation temperature and improve the performance of the REDHE. However, the unclear reverse electrodialysis (RED) characteristics of the ternary working fluid greatly block the application of the REDHE system. To this end, the ternary working fluid of LiBr-ethanol-water is respectively applied to a single-stage RED and multi-stage RED (MS-RED) stacks experiments for the first time, which clearly unveil the RED characteristics of the LiBr-ethanol-water ternary solutions under various working conditions. Both the solution compositions (solvent ratio and concentration) and the working parameters (flow velocity and feed temperature) are systematic studied. The concentration has the most excellent effect on the output performance of the RED stack, followed by temperature and flow rate. The single-stage RED could achieve a power density of 1.17 W m−2. Furthermore, the cumulative energy conversion efficiency of the MS-REDs is increased by 6.73 times from 1.48% to 11.45% as the stage number is stacked from 1 to 22 in series.

Effects of multivalent ions on hydrogen production from the salinity gradient between desalination concentrated brine and river by reverse electrodialysis

In order to simultaneously produce hydrogen and reduce the salinity of concentrated wastewater (brine) from the desalination plant, a lab-scale reverse electrodialysis (RED) hydrogen production system driven by salinity gradient energy is designed and its performance is experimentally studied. The energy conversion of the RED system is found affected by the ionic compositions of the desalination concentrated brine (DCB). The effects of ionic types (multivalent cation, anion, and phosphorous salt) and ionic concentration (from 0.01 to 0.05 M) and pH of DCB (from 5 to 11) on the hydrogen production are investigated. The results show that the existence of multivalent ions in brine significantly degrade the capability of output voltage and hydrogen production of the RED system. Compared to the control group, the additions of 0.05 mol·L−1 NaBr and 0.05 mol·L−1 FeCl3 into the simulated brines lead to the output voltage drops of 29 % and 60 %, respectively, when the current is maintained at 0.2A. Additionally, the experiment yields an MHP of 128 mL·h−1 at the current of 0.3A. Generally, the performances of the RED stack can be improved as increasing the pH of an acidic DCB, but declined as the increasing the pH of an alkaline DCB.

Sustainable power generation from salinity gradients by reverse electrodialysis: Influence of divalent ions

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 MgCl2. 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 MgCl2 compared to only NaCl, the open-circuit voltage decreases by 36.2%, and the maximum gross power density decreases by 44.8%.

Techno-economic analysis of conversing the low-grade heat to hydrogen by using reverse electrodialysis – Air gap diffusion distillation coupled method for iron and steel industry

This study devotes to the reverse electrodialysis (RED) – air gap diffusion distillation (AGDD) coupled system of converting the low-grade waste heat recovered from the steel production to hydrogen for steelmaking. This approach not only recovers waste heat but also reduces carbon emissions. To assess the feasibility of the coupled system, a techno-economic model has been developed. The influences on the levelized cost of hydrogen (LCOH) of the ion exchange membranes (cost and lifetime), the operating condition of RED stack (current density and feed solution velocity), the AGDD unit (feed solution flowrate), and the numbers of RED stacks in a multistage series system are investigated. The high price of ion exchange membrane is currently the main factor causing non-commercialization, which is almost 6.63–19.9 times larger than the LCOH of hydrogen production from renewable electricity. The membrane lifetime is the critical factor in increasing the maximum permitted membrane cost. Assuming the membranes cost is 1 RMB/m2, the optimal current density, feed solution velocity (in RED stack), and the solution volume flowrate (in AGDD unit) of are 50 A/m2, 0.00075 m/s, and 0.7 m3/h, respectively. The series systems take a considerable advantage in reducing the required AGDD units compared with one stage.

The effect of flow modes on the capture of the energy between concentrated brine and seawater by reverse electrodialysis

The discharge of concentrated brine from the desalination unit waste amounts of salinity gradient energy, which could be harvested and converted to electric energy by reverse electrodialysis (RED). However, the poor power and restricted conversion efficiency obstacle its development. A suitable flow mode of feed solutions in a RED stack can improve energy conversion efficiency. Here, the influences of co– and counter-current flow modes on the performances of a single-stage RED stack and multi-stage stacks harvesting the energy are studied in the work. Based on this, the models of flow mode affecting the RED performances are built and experimentally verified. Results show that the counter-current in a single-stage stack is better than the co-current, and the advantage is more obvious with the concentration increase of the concentrated solution, the concentration decrease of the diluted solution, and the decrease of flow rate. Besides feed parameters, the stack sizes also influence the performances of the single-stage stack in both modes. The counter-current in the multi-stage stacks is also more excellent than the co-current. However, the difference decreases with the increase of stage number. This work provides some support for utilizing the salinity gradient energy between concentrated brine and seawater.

Optimization Study on Salinity Gradient Energy Capture from Brine and Dilute Brine

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.

Recovery of transition metal ions with simultaneous power generation by reverse electrodialysis

Renewable energy processes based on salinity gradient differences possess spreading interests as an alternative to energy production methods based on fossil fuels. The reverse electrodialysis (RED) process is used for energy production by mixing seawater and river water. In the proposed solution, the spent battery effluent is applied as a high-concentrated solution for the first time, generating a potential difference in the RED stack. The high-selective cation exchange membrane for cobalt transportation in the RED system was a demanding barrier controlling the separation behaviour. The initial research confirmed the energy production ability from mixing high concentrated (HC) solution of Co2+, Li+ and Ni2+ nitrates and low concentrated (LC) solution containing chloric acid. The maximum extracted energy was estimated at 0.44 W/m2 with an energy efficiency of 45.5%. The presented method is a promising candidate for dealing with battery waste management and converting it into a valuable product such as cobalt salts with the potential for power harvesting.

Effects of electrode rinse solution on performance of hydrogen and electricity cogeneration system by reverse electrodialysis

A harvestable salinity gradient energy exists between the concentrated and diluted electrolyte solutions, which can be converted to the electromotive force of a reverse electrodialysis (RED) stack to drive the power generation and hydrogen production. The performance of a hydrogen and electricity (H&E) cogeneration system by RED method is significantly influenced by the characteristics of the electrode rinse solution (ERS). The study experimentally investigated the effects of ERS concentration, flow rate, electrolyte composition, and active additive on the system's output voltage, power density, and hydrogen and oxygen production. Besides, a surface-active substance with catalytic activity was applied for the first time to the H&E cogeneration system, aiming to decrease the overpotentials of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The results showed that the output voltage increased with an increase in ERS flow rate, but hydrogen production declined. Increasing the concentration of the ERS was beneficial to promoting the output voltage and power density, but an extremely high pH of the ERS was not conducive to hydrogen production. The electrical output performance of the H&E cogeneration system using NaOH solution as the ERS was generally better than that of the corresponding KOH solution. The addition of trioctylmethylammonium chloride (Aliquat-336) was detrimental to the electrical output performance but promoted evolution of hydrogen and oxygen. At a current of 0.3 A and an Aliquat-336 concentration of 0.4 mM, the system achieved a hydrogen production rate of 0.71 ± 0.002 mol·m−2·h−1.

A Self-Adaptive-Step-Size Incremental-Resistance-MPPT Technique for Reverse-Electrodialysis System

Salinity gradient power (SGP) is a kind of promising renewable energy source with huge potential, which can be derived through reverse electrodialysis (RED). Generally, RED stacks operate at either continuous mode or recycle mode, both of which possess respective advantages in different application scenes. Since SGP technology is still at an infant stage, there is a few research focusing on maximum-power-point-tracking (MPPT) techniques of RED stacks, which are crucial for the effective energy utilization of SGP. In this article, based on the generalized hybrid RED model, a self-adaptive-step-size incremental-resistance MPPT technique is proposed to extract maximum power from RED stacks. Not only is it simple and easy to implement but also it realizes self-adjustment of the step size to strike a balance between fast dynamic responses and small oscillations at a steady state. Moreover, according to the unique intrinsic features of RED stacks, the systematic design principles of the sampling interval and scaling factor are detailed, which help facilitate a fast and stable system. Various tests with the proposed technique under different parameter settings, as well as tests with other conventional MPPT techniques, are conducted on a RED stack prototype to validate the effectiveness of the proposed MPPT.

Energetic Valorisation of Saltworks Bitterns via Reverse Electrodialysis: A Laboratory Experimental Campaign.

Concentrated bitterns discharged from saltworks have extremely high salinity, often up to 300 g/L, thus their direct disposal not only has a harmful effect on the environment, but also generates a depletion of a potential resource of renewable energy. Here, reverse electrodialysis (RED), an emerging electrochemical membrane process, is proposed to capture and convert the salinity gradient power (SGP) intrinsically conveyed by these bitterns also aiming at the reduction of concentrated salty water disposal. A laboratory-scale RED unit has been adopted to study the SGP potential of such brines, testing ion exchange membranes from different suppliers and under different operating conditions. Membranes supplied by Fujifilm, Fumatech, and Suez were tested, and the results were compared. The unit was fed with synthetic hypersaline solution mimicking the concentration of natural bitterns (5 mol/L of NaCl) on one side, and with variable concentration of NaCl dilute solutions (0.01-0.1 mol/L) on the other. The influence of several operating parameters has also been assessed, including solutions flowrate and temperature. Increasing feed solutions' temperature and velocity has been found to lower the stack resistance, which enhances the output performance of the RED stack. The maximum obtained power density (corrected to account for the effect of electrodic compartments, which can be very relevant in five cell pairs laboratory stacks) reached around 10.5 W/m2cellpair, with FUJIFILM Type 10 membranes, temperature of 40 °C, and a fluid velocity of 3 cm s-1 (as empty channel, considering 270 μm thickness). Notably, the present study results confirm the large potential for SGP generation from hypersaline brines, thus providing useful guidance for the harvesting of SGP in seawater saltworks all around the world.

A generalized disjunctive programming model for the optimal design of reverse electrodialysis process for salinity gradient-based power generation

Reverse electrodialysis (RED) is an emerging electro-membrane technology that generates electricity out of salinity differences between two solutions, a renewable source known as salinity gradient energy. Realizing full-scale RED would require more techno-economic and environmental assessments that consider full process design and operational decision space from the RED stack to the entire system. This work presents an optimization model formulated as a Generalized Disjunctive Programming (GDP) problem that incorporates a finite difference RED stack model from our research group to define the cost-optimal process design. The solution to the GDP problem provides the plant topology and the RED units’ working conditions that maximize the net present value of the RED process for given RED stack parameters and site-specific conditions. Our results show that, compared with simulation-based approaches, mathematical programming techniques are efficient and systematic to assist early-stage research and to extract optimal design and operation guidelines for large-scale RED implementation.