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BES for H2O2 production has great potential in the future due to its high efficiency, energy efficiency, and environmental friendliness because it turns waste into useful chemicals without any energy input.

Seawater is a cost-effective and abundant electrolyte used as an electrode rinse solution to enable optimum utilization of reverse electrodialysis (RED). However, it is associated with several limitations, including the use of precious electrode materials, and its long-term stability must be addressed prior to its application in the field of seawater technology. In this context, a novel RED based on carbon electrodes was designed, and the experimental conditions were optimized for maximizing the harvesting of energy with aquaculture wastewater disinfection and recycling. The power obtained by RED, with a current density of 30 A/m

In a large-scale reverse electrodialysis (RED) system comprising several hundreds of cell pairs, the contribution of electrode resistance to total resistance is very small compared to that in typical electrochemical cells (e.g., fuel cell and battery). This feature indicates the low susceptibility to both electrocatalytic ability of the electrode and solution conductivity, and to the geometrical area of the electrode as well. Therefore, in this work, we introduce an asymmetrical electrode system, where the geometrical area of the cathode is smaller than that of the anode. Since the cathode is highly vulnerable to significant inorganic scaling due to the high pH conditions during water reduction and crossover of multivalent ions in the natural feed solution, it is expected that minimizing the contact area between the electrode and feed solution by reducing the geometrical area of the cathode can afford more stable electrode reaction and electric power during long-term operation of RED. We measured the changes in electric power as a function of various areas of the cathode in lab- (100 cell pairs) and large-scale (1000 cell pairs) RED systems, which confirmed that even though the cathode area corresponds to 60% of the individual area of the ion-exchange membrane (IEM), the maximum power was obtained with only 3% power loss. In addition, the surface properties and permselectivity of a shielding membrane at the cathode were analyzed by X-ray photoelectron spectroscopy (XPS) and membrane potential measurement to verify the stability of the IEM under higher current density. We recommend the use of the asymmetric electrode system with a bipolar membrane (BPM) to suppress inorganic scaling around the cathode. The high current density achieved by reducing the size of the cathode can induce vigorous water splitting in the BPM, which leads to more effective blocking crossover of the multivalent and hydroxide ions. It can hence be used to design a highly stable electrode system for the long-term operation of a pilot-scale RED system fed with natural feed solutions.

The voltage produced from the salinity gradient in reverse electrodialysis (RED) increases proportionally with the number of cell pairs of alternating cation and anion exchange membranes. Large-scale RED systems consisting of hundreds of cell pairs exhibit high voltage of more than 10 V, which is sufficient to utilize water electrolysis as the electrode reaction even though there is no specific strategy for minimizing the overpotential of water electrolysis. Moreover, hydrogen gas can be simultaneously obtained as surplus energy from the electrochemical reduction of water at the cathode if the RED system is equipped with proper venting and collecting facilities. Therefore, RED-driven water electrolysis system can be a promising solution not only for sustainable electric power but also for eco-friendly hydrogen production with high purity without CO2 emission. The RED system in this study includes a high membrane voltage from more than 50 cells, neutral-pH water as the electrolyte, and an artificial NaCl solution as the feed water, which are more universal, economical, and eco-friendly conditions than previous studies on RED with hydrogen production. We measure the amount of hydrogen produced at maximum power of the RED system using a batch-type electrode chamber with a gas bag and evaluate the interrelation between the electric power and hydrogen energy with varied cell pairs. A hydrogen production rate of 1.1 × 10−4 mol cm−2 h−1 is obtained, which is larger than previously reported values for RED system with simultaneous hydrogen production.

Pore-filling ion exchange membranes are fabricated by complicated and energy-inefficient processes, use of large amounts of polar organic solvents, and optionally post-modification using acid or base. For green fabrication of pore-filling anion exchange membranes (PAEMs), we optimized the process parameters such as pretreatment time, impregnation time, water amount, and photo-polymerization rate of each step using roll to roll (R2R) equipment. Based on these optimized process parameters, a PAEM of 57.5 cm width and 39 μm thickness completely filled with a photo-cured electrolyte polymer was fabricated by aqueous pretreatment and by using an impregnation solution without toxic organic solvents. The impregnation step was conducted along with photo-polymerization at a line speed of 0.3 m/min without repeated impregnation with R2R equipment. The IEC, resistance, and permselectivity of this PAEM were similar to those of handmade PAEMs. The PAEM exhibited chemical stability in the pH range of 0–12. In addition, the reverse electrodialysis stack assembled with these PAEMs exhibited a higher power density than a stack of commercial ion exchange membranes. These results demonstrate that industrial-scale PAEM can be fabricated through a rapid, simple, environmentally friendly, and energy-efficient R2R process.

It is generally accepted that the effect of electrode resistance is not predominant in determining the performance of reverse electrodialysis (RED), because the contribution of electrode resistance to total internal resistance decreases as the number of cell pairs increases. However, this is not true under the condition in which gas is continuously produced by water electrolysis owing to the large stack voltage in pilot-scale applications. We verified that the bubble resistance of the electrode spacer in a conventional endplate causes the electric power of a RED system with 1000 cells to decrease by more than 20% under the specific condition in which the outermost feed solution (OFS) at both electrodes and the electrode solution (ES) are river water. This configuration, called OFS(river)/ES(river), is the best for minimizing inorganic scaling and toxic gas evolution. Another problem associated with the conventional endplate is fluid congestion owing to very narrow spaces, which causes sudden pH changes and deteriorates further with inorganic scaling. To address these issues, we removed the electrode spacer from the electrode system and utilized an open-type endplate with interconnected open spaces. This endplate maintained high electric power without the bubble resistance and suppressed the abrupt changes in the pH around the electrodes and the shielding membranes. We believe that our approach will be useful in the search for an optimum electrode design for RED systems on the industrial scale.

The utilization of large amounts of volatile organic solvents and the complicated process required for industrial manufacturing of ion-exchange membranes necessitate the development of simple, rapid, and environmentally friendly fabrication methods such as those based on photopolymerization. We employed hydrolytic sol–gel reactions between ammonium- and acrylamide-functionalized silane coupling agents to synthesize water-soluble siloxane resins that exhibit high condensation levels (>80%) and comprise oligomers with molecular weights below 2000 Da. These resins were then mixed with a hydrophilic monomer bearing ammonium and acrylamide groups, and porous polyethylene substrates were impregnated with the resulting mixtures and then irradiated with ultraviolet light. The hydrophilicity, mechanical strength, and other properties of the resulting membranes depended on the resin composition, indicating that the substrate pores were efficiently filled with the prepared resins and further suggesting that the membrane performance could be effectively altered by varying the resin composition. Moreover, the obtained membranes exhibited chemical stability in the pH range between 0 and 11 and in hot water at 60 °C. The reverse electrodialysis stack consisting of these membranes showed higher power density than a stack of commercial membranes. Therefore, it can be concluded that without employing volatile organic solvents for reverse electrodialysis, the developed technique is well-suited for the fabrication of ion-exchange membranes.

Irreversible faradic reactions in reverse electrodialysis (RED) are an emerging concern for scale-up, reducing the overall performance of RED and producing environmentally harmful chemical species. Capacitive RED (CRED) has the potential to generate electricity without the necessity of irreversible faradic reactions. However, there is a critical knowledge gap in the fundamental understanding of the effects of operational stack voltages of CRED on irreversible faradic reactions and the performance of CRED. This study aims to develop an active control strategy to avoid irreversible faradic reactions and pH change in CRED, focusing on the effects of a stack voltage (0.9-5.0 V) on irreversible faradic reactions and power generation. Results show that increasing the initial output voltage of CRED by increasing a stack voltage has an insignificant impact on irreversible faradic reactions, regardless of the stack voltage applied, but a cutoff output voltage of CRED is mainly responsible for controlling irreversible faradic reactions. The CRED system with eliminating irreversible faradic reactions achieved a maximum power density (1.6 W m-2) from synthetic seawater (0.513 M NaCl) and freshwater (0.004 M NaCl). This work suggests that the control of irreversible faradic reactions in CRED can provide stable power generation using salinity gradients in large-scale operations.

Despite significant advances in the field applications of reserve electrodialysis (RED) to produce salinity gradient power, net energy production remains an issue owing to limitations such as high energy requirement for high flow rates of feed solutions, and severe fouling and pressure build up when thin spacers are used. Therefore, to maximize the performance and efficiency of energy harvesting in the RED, a cascaded RED stack, with multiple stages between the anode and cathode electrodes, was investigated. In cascaded stacks, 100-cell paired stacks were divided into several stages, so the feed water flowed into the first stage, and the effluent from the first stage was then reused in the next stages. This cascaded stack could overcome the typical drawbacks of RED (large amount of feed water required, intensive pumping energy, and low net energy production). Although 25% of the feed water volume was used in the 4-stage cascaded stack (100-cell-pairs) compared to the conventional stack (100-cell-pairs with a parallel flow operation), much more energy was produced with the 4-stage cascaded stack. The net power density and net specific energy with the 4-stage cascaded stack were the highest at 0.5 cm/s (0.48 W/m2) and 0.25 cm/s (0.06 kWh/m3), respectively. This is very promising for the practical application of RED since feed water volumes can be greatly reduced, which could reduce the burden on the feed water pretreatment step. Consequently, we can build a compact RED plant with smaller pretreatment processes and fewer RED unit stacks.

Urine dilution is often performed to avoid clogging or scaling of pipes, which occurs due to urine's Ca2+ and Mg2+ precipitating at the alkaline conditions created by ureolysis. The large salinity gradient between urine and flushing water is, theoretically, a source of potential energy which is currently unexploited. As such, this work explored the use of a compact reverse electrodialysis (RED) system to convert the chemical potential energy of urine dilution into electric energy. Urine' composition and ureolysis state as well as solution pumping costs were all taken into account. Despite having almost double its electric conductivity, real hydrolysed urine obtained net energy recoveries ENet of 0.053-0.039 kWh/m3, which is similar to energy recovered from real fresh urine. The reduced performances of hydrolysed urine were linked to its higher organic fouling potential and possible volatilisation of NH3 due to its high pH. However, the higher-than-expected performance achieved by fresh urine is possibly due to the fast diffusion of uncharged urea to the freshwater side. Real urine was also tested as a novel electrolyte solution and its performance compared with a conventional K4Fe(CN)6/K3Fe(CN)6 couple. While K4Fe(CN)6/K3Fe(CN)6 outperformed urine in terms of power densities and energy recoveries, net chemical reactions seemed to have occurred in urine when used as an electrolyte solution, leading to TOC, ammonia and urea removal of up to 13%, 6% and 4.4%, respectively. Finally, due to the migration of K+, NH4+ and PO43-, the low concentration solution could be utilised for fertigation. Overall, this process has the potential of providing off-grid urine treatment or energy production at a household or building level.

The direct integration of two-dimensional nanostructures into macroscopic porous carbon substrates is essential for their practical use in potential applications, which is a big challenge due to the difficulty of securing uniform coating layers. In this work, we demonstrate a very simple and effective method for the direct coating of MoS2 onto the surface of porous carbon structures having nano-sized pores, such as vertically aligned carbon nanotube arrays. A uniform coverage of MoS2 over carbon substrates was achieved by chemical vapor deposition of gaseous species derived from starting precursors in a closed reactor. Transmission electron microscopy images, X-ray diffraction data, and Raman spectra confirmed the formation of highly crystalline MoS2 layers. X-ray photoelectron and energy dispersive X-ray spectroscopies revealed highly uniform MoS2 layers over the whole surface of the carbon substrates. Our approach is also applicable for the synthesis of MoS2/carbon fiber paper (CFP) hybrid structures. The electrochemical tests showed that the as-synthesized MoS2/CFP structures can serve as highly active cathodes for reverse electrodialysis.

High hydrogen production rate and energy recovery were accomplished in a tubular microbial electrolysis cell (MEC) equipped with a robust membrane electrode assembly (MEA). The current and the hydrogen production of non-flexible MEAs, simply fabricated by directly brushing a catalyst on a self-supporting tubular membrane, were compared with those of a typical MEA, where a cathode is physically combined with a membrane. Current of 34 ± 2 mA (1.79 ± 0.05 A/m2) and coulombic efficiency of 98.5 ± 1.0% were achieved in non-flexible MEAs, outperforming the typical MEA under fed-batch mode. The MEA, having a durable coating layer, also showed an enhanced hydrogen production rate and electric energy recovery with values of 0.18 ± 0.03 m3/m3-d and 151.9 ± 1.0%, respectively, even for low strength domestic wastewater (dWW) treatment in the continuous-flow mode. These outcomes were similarly maintained in the case of using seawater, which is a good candidate for an economical and environmentally suitable catholyte.

Reverse electrodialysis (RED) is an emerging technology that can generate electricity from the mixing of two water streams (i.e., the concentrated and the diluted streams) with salinity gradient. I...

We have successfully exploited the Michael-type addition reaction between catechol and DABCO (1,4-diazabicyclo-[2,2,2]octane) molecules under alkaline conditions for the formation of new quaternary ammonium (QA) groups in an anion-exchange membrane. The anion-exchange membranes (AEMs) were prepared using the pore-filling method by addition of electrolytes (vinyl benzyl trimethylammonium chloride (VBTMA), dopamine methacrylamide (DMA) bearing a catechol group, and ethylene glycol diacrylate as a cross-linker) to a porous substrate. The formation of new QA groups by the reaction of DABCO with catechol components was confirmed by characterization of new peaks in the Fourier transform infrared spectra of the AEMs. The DABCO-bound AEM demonstrated a significant decrease in area resistance (0.4 Ω·cm2) and increase in permselectivity (94%). Furthermore, the electrochemical properties of the AEMs could be controlled by altering the concentrations of VBTMA and DMA and the formation of new bonds between DMA and DAB...

We report the direct chemical vapor deposition of graphitic carbon-encapsulating carbonate apatite nanowires (GCECANs)/hexagonal portlandite-phased Ca(OH)2 hybrid structures from CaCO3 powder at 900 °C. The formation mechanism of the GCECANs is investigated in detail through a structural and morphological characterization of the final products. Spectroscopic analyses elucidate the effect of H2 concentration in the reactor on the transformation of the calcite-phased CaCO3 into vaterite-phased CaCO3 and subsequently portlandite-phased Ca(OH)2. The results show that GCECANs are formed on the surface of the derived Ca(OH)2. It is especially remarkable that a higher H2 concentration results in the precipitated growth of such hybrid structures. Microscopic images show that GCECANs 20 nm in diameter grew up to 3 μm in length along the direction corresponding to the [001] plane of the hexagonal apatite crystal. In addition, the electrical properties of the GCECANs are measured by using an electrode with 150 nm gap.

Reverse electrodialysis (RED), based on non-precious electrodes, was applied to disinfect domestic aquaculture wastewater. It was found that treatment could be achieved either by an anodic reaction of electro-generated sodium hypochlorite (NaClO) or via a cathodic reaction of electro-generated hydrogen peroxide (H2O2). Without circulation, the disinfection rate was sub-optimal and depended on the anodic and cathodic reactions, reaching 82 ± 5% at the anode (0.3–2.9 mg/L of chlorineDPD, pH 3.2 ± 0.4) and 59 ± 7% at the cathode (2.9–8.7 mg/L of H2O2, pH 10.7 ± 0.3). In contrast, a high removal efficiency of ≥99 ± 1% was obtained when anodic and cathodic solutions were circulated due to the synergetic effect between HClO and H2O2 (0.1–2.1 mg/L of chlorineDPD, 3.9–4.9 mg/L of H2O2, pH 7.8 ± 0.2). Both operating modes resulted in a stable power production of 6 ± 0.5 W/m2. These results support the view that RED can offer a cost-effective and energy-efficient option for disinfecting aquaculture wastewater.

This report describes direct seawater electrolysis (DSE) wherein natural seawater is used as a catholyte without filtration or pretreatment; seawater is acidified to a pH of 2 while hydroxide ions are produced at the cathode by the hydrogen evolution reaction (HER). It results from the cooperative effect of hydroxide ions trapped through inorganic precipitation at the cathode and proton flux from water dissociation in a bipolar membrane (BPM; used as a separator). The acidification of the catholyte in the proposed BPM-DSE substantially mitigates cathode passivation, eliminates the requirement of additional processes for treatment of inorganic precipitates dispersed in the catholyte, and reduces the cathode potential ( E c ) required for the HER to enable long-term DSE. The BPM in this system plays a critical role in maintaining the electrolyte concentration, suppressing the chlorine evolution reaction (ClER), and maximizing the oxygen evolution reaction. These findings are expected to suggest a breakthrough toward large-scale operation of DSE that successfully overcomes challenges such as energy consumption, inorganic precipitation, ClER, and corrosion.

We report the high-yield and large-area synthesis of a spaghetti-like carbon nanotubes (CNTs) on macroscopic Cu substrates (foil and foam) using a Cu-Sn alloy catalyst. In addition, we investigate the corrosion properties of the as-synthesized CNT/Cu foil system in 0.6 M NaCl solution. Electrochemical analysis showed that the corrosion resistance of the CNT/Cu foil system improved by a factor of ∼100 compared to the as-received Cu foil. Thus, it is concluded that a dense network of CNT was uniformly coated on the Cu foil and this coating functioned as an efficient barrier to corrosion under simulated seawater conditions.

Removal of scale-forming ions (e.g., Ca2 +, Mg2 +) from seawater using a bioelecrochemical system (BES) was investigated in a fed-batch and a continuous mode. In the fed-batch mode, Ca2 + removal with different anolyte buffers at different external resistances (10 Ω and 1 kΩ) was evaluated. As a result, Ca2 + was effectively removed with PBS (phosphate buffer solution) and PIPES (piperazine-N,N′-bis(2-ethanesulfonic acid) buffer solution. However, the removal of Ca2 + with PBS was not solely due to current generated from the anode but also from precipitation induced by combining Ca2 + with phosphate ions transferred from the anode chamber while the removal of Ca2 + with PIPES entirely relies on a cathodic reaction. Continuous removal of Ca2 + and Mg2 + with PIPES was more effective than the fed-batch mode with removal efficiencies of > 97 ± 2% (Ca2 + removal) and 98 ± 1% (Mg2 + removal). The XRD spectra revealed that the precipitates were mainly composed of brucite (Mg(OH)2), calcite, and aragonite (CaCO3). These results indicate that BES could be a promising way to remove scale-forming ions that can promote inorganic fouling in membrane-based processes.

Global warming has become a serious threat biosphere and effective measures are required to mitigate its intensification. To this end, carbon capture and sequestration (CCS) is a promising technology, while post-combustion capture (PCC) has been developed from CCS. However, an energy penalty during the regeneration step of the CO2 absorbent has remained a critical problem. In the present study, a lab-scale test was conducted on carbon capture with reverse-electrodialysis (CCRED) to evaluate its potential to overcome the technical and economic drawbacks of CCS and RED. The results show that a normalized peak power density of 1 W/m2, equal to 328.6 kJ/kgCO2, could be obtained. The peak power density was 2000-fold higher than that in previous studies. By utilizing CO2 as an energy source in CCRED, this novel process can compensate for the energy penalty in conventional CCS.

In this work, we demonstrate the large-area synthesis of graphitic filamentous nanocarbon-aligned carbon thin layer (GFNACTL) on Cu foil by chemical vapor deposition of C 2 H 2 at 700 °C at 5 Torr pressure. The thickness of the GFNACTL can be controlled to vary in the range 50–4000 nm by varying the synthesis time. The graphitic filamentous nanocarbon with outer diameters ∼10–20 nm have highly oriented and well-connected graphitic structures that are stacked perpendicular to the growth direction. This result shows that the presence of a native oxide layer on the Cu foil was beneficial for the GFNACTL growth. Our approach can be extended to the one-pot synthesis of GFNACTL/carbon nanotube (CNT) forest hybrid thin films. The tip growth of CNTs with diameters of ∼50 nm was catalyzed on the GFNACTL by Cu 41 Sn 11 nanoparticles. Corrosion measurements were performed in 0.6 M NaCl solution. Electrochemical analysis revealed a strong improvement in corrosion resistance as compared to pure Cu specimens, indicating the superior uniformity and promise of the GFNACTL/CNT forest hybrid thin films for application as a protective coating.

Fouling occurred on the ion-exchange membranes under practical condition, Reversible fouling occurred on the CEM, Irreversible fouling occurred on the AEM.

Pore-filling ion-exchange membranes have been produced via complex, low energy efficient, and toxic processes, including repetitive impregnation to fully fill the porous substrates with polymer ele...

Experimental and numerical studies on pressure drop in Reverse electrodialysis (RED) were performed. In this study, a module with 200 unit cells is considered for the demonstration of bench-scale RED module and two different unit cell configurations are utilized. Pressure drop through the module is measured by varying flow rates. For evaluating the hydrodynamic characteristics in the unit cell, a numerical simulation is also conducted and the simplified method using a porous media model is employed to simulate the channel filled with spacer. Due to the insertion of spacer and narrow channel, great pressure loss occurs along the unit cell. Based on estimated pressure data, high pressure difference between seawater and fresh water channel takes place locally in the unit cell configuration with crossflow direction, leading to a leakage problem through the membrane and finally degradation in the output power. Consequently, it is confirmed that the unit cell configuration is one of the important design parameters in a RED module.

In this work, we describe the direct growth of carbon nanofilaments by the catalytic decomposition of ethanol on untreated polycrystalline Ni foil. Our work focuses on the effects of synthesis conditions on the growth of the carbon nanofilaments and their growth mechanism. Direct growth of carbon nanotubes (CNTs) is more favorable on lower-purity Ni foil. The highest yield was obtained at approximately 750 °C. The average diameter of the CNTs was approximately 20–30 nm. Raman spectra revealed that the increase of H2 concentration in the carrier gas and synthesis temperature induced the growth of better-graphitized CNTs. Additionally, we investigated the anticorrosion properties of as-prepared products under simulated seawater conditions. The corrosion rate of the CNT/Ni foil system was maximally 50–60 times slower than that of the as-received Ni foil, indicating that the CNT coating may be a good candidate for corrosion inhibition.

Performance of graphite foil electrodes coated by porous carbon black (i.e., Vulcan) was investigated in comparison with metal electrodes for reverse electrodialysis (RED) application. The electrode slurry that was used for fabrication of the porous carbon-coated graphite foil is composed of 7.2 wt% of carbon black (Vulcan X-72), 0.8 wt% of a polymer binder (polyvinylidene fluoride, PVdF), and 92.0 wt% of a mixing solvent (dimethylacetamide, DMAc). Cyclic voltammograms of both the porous carbon (i.e., Vulcan)-coated graphite foil electrode and the graphite foil electrode without Vulcan showed good reversibility in the hexacyanoferrate(III) (i.e., Fe(CN)63−) and hexacyanoferrate(II) (i.e., Fe(CN)64−) redox couple and 1 M Na2SO4 at room temperature. However, anodic and cathodic current of the Vulcan-coated graphite foil electrode was much higher than those of the graphite foil electrode. Using a bench-scale RED stack, the current–voltage polarization curve of the Vulcan-coated graphite electrode was compared to that of metal electrodes such as iridium (Ir) and platinum (Pt). From the results, it was confirmed that resistance of four different electrodes increased with the following order: the Vulcan-coated graphite foil

The generation of salinity gradient power (SGP) is a promising technique to extract energy from either seawater or reverse osmosis (RO) brine. There are two methods for harvesting SGP, including reverse electrodialysis (RED) and pressure retarded osmosis (PRO). Although they have been individually investigated, few works have been done to compare their fouling behaviors under similar conditions. Accordingly, this study intended to compare RED and PRO processes using various low salinity (LS) solutions and high salinity (HS) solutions in terms of power density and fouling potential. Experiments were carried out in bench-scale RED and PRO systems. Three types of LS solutions including deionized water (DW), wastewater (WW), and wastewater reverse osmosis brine (WB) and two types of HS solutions including seawater (SW) and seawater reverse osmosis brine (SB) were considered. The power density was measured under non-fouling (initial) and fouling conditions. Results indicated that the power density for the PRO was higher (1.09– 3.24 W/m2) than that for the RED (0– 1.66 W/m2) under the non-fouling condition. However, the loss of power density due to fouling was smaller in RED (0– 11.2%) than in PRO (14.2– 58.7%). The use of WB as the LS solution resulted in low power density in both RED process (

Reverse electrodialysis (RED) is an emerging electrochemical process for harnessing salinity gradient power. For the commercialization of the RED process, the development of a highly efficient RED stack at a given flow rate is crucial. For this purpose, we first evaluated the performance of a RED stack according to the number of cell pairs at a given flow rate to improve the net power and specific energy (SE). Integrating the number of cell pairs at a given flow rate caused an increase in the electrical potential, and the net power was converged to the limiting value. The net SE was 0.06 kWh/m3 with 100 cell pairs at a flow rate of 100 mL/min. The levelized cost of electricity (

The fouling characteristics of dissolved organic matter (DOM) in the fresh water and seawater compartments of the reverse electrodialysis (RED) system were investigated under natural water conditions. The salinity gradient power generation was governed monovalent ions whereas multivalent ions strongly contributed to the fouling formation of the ion-exchange membranes (IEMs). The partial deposition of DOM within the membrane pores during its passage from the fresh water compartment to the seawater compartment facilitated the fouling formation of the IEMs. Despite of the similar DOC losses in fresh water (DOC loss = 20%) and seawater (DOC loss = 22%) through the RED system, the colour variations of the anion-exchange membranes (AEMs) and spacers in contact with fresh water were more noticeable than those in contact with seawater. These results indicate that the deposition of hydrophobic DOM components onto the AEM surfaces water may lead to the increases in the pressure drop of the fresh water compartment and the decreases in the power density of the RED system. Therefore, an appropriate pre-treatment strategy capable of mitigating membrane fouling by hydrophobic DOM components seemed to be indispensable to maintain constantly the performance of the RED system under natural water conditions.

Here we describe the development and testing of a hybrid system that combines microbial electrolysis and reverse electrodialysis (RED) to benefit energy production from seawater. A tubular, continuous-flow, microbial electrolysis cell (MEC) was used prior to RED to remove multivalent ions (Ca2+ and Mg2+) that are known to decrease RED power generation due to high electric membrane resistance. When a membrane electrode assembly was applied to reduce external resistance in the MEC, Ca2+ and Mg2+ were effectively removed with efficiencies of 84 ± 5% and 99 ± 5% (current density of 4.0 ± 0.2 A/m2), respectively, and H2 was simultaneously generated. A high H2 (purity > 99.5%) production rate (2.00 ± 0.09 m3/m3·d) at an applied voltage of 1.5 V, and maximum electrical energy efficiency (169 ± 4%) was accomplished at an applied voltage of 0.9 V and with an anode hydraulic retention time of 6 h. Effluent (47 mS/cm) from the MEC was fed to the RED stack as a high-concentration solution and the conductivity of treated seawater was lower than untreated seawater (53.7 mS/cm) due to Ca2+ and Mg2+ elimination from the seawater. Despite its lower conductivity, treated seawater produced higher power (0.29 W/m2, 26% increase) compared to untreated seawater due to the removal of Ca2+ and Mg2+. Therefore, the MEC is superior to other energy-consuming seawater pretreatment system as it produces energy during seawater pretreatment and successfully integrates with RED to enhance power generation.

This study reports the direct synthesis of MoS2 thin film on Al foil by chemical vapor deposition in a closed reactor. The electrochemical properties of the thin film were analyzed using reverse electrodialysis between salt water and fresh water. Microscopic and spectroscopic analyses revealed the porous and defective surface morphologies and layered crystalline structure of the MoS2 thin film. In cross-sectional TEM images, the MoS2 thin film was random and obliquely layered on the surface of Al foil native oxide. According to electrochemical tests, the maximum gross power density of MoS2/Al was approximately 34 W/m2, 54% higher than that of the as-received Al and 78% superior to the bulk MoS2 disk. The results confirmed that MoS2 was uniformly coated on the Al foil. MoS2/Al is a superior and inexpensive cathode for reverse electrodialysis, representing a new energy application of MoS2.

To properly design reverse electrodialysis (RED) stacks, modeling of ion transport and prediction of power generation on the single RED stack are very important. Currently, the Nernst–Planck equation is widely adopted to simulate ion transport through IEMs. However, applying typical Nernst-Planck equation is not proper to analyze ion transport through the heterogeneous thin-composite pore-filling membrane because of the non-conductive site in the membrane matrix. Herein, we firstly introduced modified Nernst-Planck equation by addressing conductive traveling length (CTL) to simulate the ion transport through the thin-composite pore-filling membranes and the performance of a single RED stack with the same membranes. Also, 100 cell-pairs of RED stacks were assembled to validate modified Nernst-Planck equation according to the flow rate and membrane types. Under the OCV condition, the conductivity of the effluents was measured to validate the modified Nernst-Planck equation, and differences between modeling and experiments were less than 1.5 mS/cm. Theoretical OCV and current density were estimated by using modified Nernst-Planck equation. In particular, hydrophobicity on the surface of the heterogeneous membrane was considered to describe ion transport through the pore-filling membranes. Moreover, power generation from RED stacks was calculated according to the flow rate and the number of cell pairs.

Reverse electrodialysis (RED) has vast potential as a clean, nonpolluting, and sustainable renewable energy source; however, pilot-scale RED studies employing real waters remain rare. This study reports the largest RED (1000 cell pairs, 250 m2) with municipal wastewater effluent (1.3–5.7 mS/cm) and seawater (52.9–53.8 mS/cm) as feed solutions. The RED stack was operated at a velocity of 1.5 cm/s and the pilot plant produced 95.8 W of power (0.38 W/m2 total membrane or 0.76 W/m2cell pair). During operation of the RED, the inlet design of the stack, comprising thin spacers, and the water dissociation reaction at the cathode were revealed as vulnerabilities of the stack. Specifically, pressure drops at the fluid inlet parts had the most detrimental effects on power output due to clogged spacers around the inlet parts. In addition, precipitates resulting in inorganic fouling were inevitable during the water dissociation reaction due to significant potential generated by the stack in the cathode chamber. Na+ and Cl− accounted for the majority of ions transferred from seawater to wastewater effluent through ion exchange membranes (IEMs). Moreover, some divalent cations in seawater, Mg2+ and Ca2+, were also transferred to the wastewater effluent. Some organics with relatively low molecular weights in the wastewater effluent passed through the IEMs, and their hydrophobic properties elevated the specific UV absorbance (SUVA) level in the seawater.

Studies on the fabrication of nanoscaled calcium aluminate materials and their growth mechanisms still present key challenges. In this work, we report the catalyst-free chemical vapor deposition of calcium aluminate nanostructures including nanoflakes and nanochains during the carbonization of woody biomass at 1500 °C in H2. The mixture of Al and Al2O3 is prepared as a starting material with henequen fibers for the synthesis. Hexagonal CaAl12O19 nanoflakes and monoclinic CaAl2O4 nanochains are found as main products after the synthesis. The CaAl12O19 nanoflakes have thickness of approximately 100 nm. The CaAl2O4 nanochains exhibit a regular periodic structure that is composed of nanowires and nanobeads of 100 nm and 300 nm in diameter, respectively. The nanochains oriented along the (100) plane grow to lengths of dozens of microns. The surface of nanochains is covered by an amorphous layer with a thickness of approximately 5 nm. Cathodoluminescence measurement reveals that both CaAl12O19 nanoflakes and CaAl2O4 nanochains have the potential in optical applications.

Direct integration of nanostructures into macroscopic substrates is very important for their practical applications. In this work, we report a simple method that can be introduced for the Sn-catalyzed growth of alumina nanowires on ceramic substrates such as porous disk, monolith, and foam. Our study focuses on the role of the Sn catalysts in the formation mechanisms governing nanowire growth. Using the proposed approach, hair- or grass-like tufts of 20 nm diameter nanowires grow on the surface of the ~3 μm diameter Sn particles, in a tip growth mechanism. The nanowires of α-phased polycrystalline structure grow and are packed via a complex process involving batch-by-batch, branching, and amalgamation growth. The detailed observations reveal that the Sn catalyst is key to tailoring the growth patterns of the nanowires. In addition, cathodoluminescence studies highlight the potential optical applications of the alumina nanowires.

Energy and cost effective pretreatment of seawater is essential for any desalination plant to convert seawater into clean water successfully. This study shows a way to pretreat seawater without excessive input of electrical energy or high pressure; it uses a bioelectrochemical cell with two chambers, divided by an anion exchange membrane (AEM). When bacteria attached on the anode produce current using organic matter as a source of fuel, hydroxyl ions can be generated in the cathode chamber, which can increase the alkalinity of the catholyte (seawater); scale-forming ions such as Ca 2 + and Mg 2 + in seawater can be removed by forming precipitates in the cathode chamber. Our results show that 84% of Ca 2 + and 37% of Mg 2 + in seawater can be effectively removed while treating wastewater in the anode chamber. These results indicate a new method to pretreat seawater without external energy input since the cell accomplishes selective removal of divalent cations using an electrochemical cathode reaction. This study provides evidence that this new method can be a viable option for membrane based seawater pretreatment and desalination processes to significantly mitigate scale problems of membranes.

In the present study, a novel reverse electrodialysis (RED) stack with ultrathin lab-made pore-filling membranes and a high-open-area spacer was proposed to enhance the gross power density. The proposed stack had much lower internal resistance than a typical RED stack at optimum flow rates of seawater and river water. Therefore, a gross power density of 2.4 W m−2 was achieved.

Molybdenum disulfide (MoS2) is considered to be promising two-dimensional material in potential applications because of its superior properties. Herein, our work suggests another important application as an inexpensive and highly active cathode material in reverse electrodialysis (RED). The MoS2 (8, 36, 76, 100 nm)/rutile-phase TiO2/Ti (MoS2/rpTiO2/Ti) heterostructures were successfully prepared with the randomly layered and oblique 1T/2H-MoS2 by one-step chemical vapor deposition of starting precursors in a closed reactor. The MoS2/rpTiO2/Ti reveals a thickness-dependent RED performance. Moreover, the MoS2 synthesis after sulfur modification of Ti surface (MoS2/smrpTiO2/Ti) increases the gross power density and reduces internal resistance of RED stack, indicating that the interfacial engineering between MoS2 and rpTiO2 improves both the catalytic activity and charge transfer efficiency. As a result, the highest gross power density of approximately 270 W/m2electrode was achieved using a RED stack mounted with 50-cell-pair of ion exchange membranes, which is comparable to that of platinum. Our work not only suggests that the MoS2/smrpTiO2/Ti heterostructure shows grate potential in RED stack, but also provides the importance of interface engineering between MoS2 and TiO2 through sulfate-bridge and sulfur-doping in MoS2-based electrocatalytic devices.

An ideally designed scaffold for tissue engineering must be able to provide an environment that recapitulates the physiological conditions to control stem cell function. Here, we compared vertically aligned single-crystal apatite nanowires sheathed in graphitic layers (SANGs) with single-crystal apatite nanowires (SANs), which had the same geometric properties as--but differing nanotopographic surface chemistry than--SANGs, in order to evaluate the effect of the graphitic layer on the behavior of human mesenchymal stem cells (hMSCs). The difference in nanotopographic surface chemistry did not affect hMSC adhesion, growth, or morphology. However, hMSCs were more effectively differentiated into bone cells on SANGs through interaction with graphitic layers, which later degraded and thereby allowed the cells to continue differentiation on the bare apatite nanowires. Thus, SANGs provide an excellent microenvironment for the osteogenic differentiation of hMCS.

We report the controlled synthesis of bismuth–tin (Bi–Sn) nanostructures sheathed in graphitic shells that resemble carbon nanotubes (CNTs). Our approach is based on a simple catalytic chemical vapor deposition over a mixture of Bi2O3 and SnO2 supplied as starting materials. Shape control of the nanostructures strongly relies on the weight ratio of Bi2O3 and SnO2. Sheathed nanoparticles and nanorods are formed at SnO2 to Bi2O3 weight ratios of less than 4:1. They are composed of two separate crystals: rhombohedral Bi and tetragonal Sn19Bi crystals. On the other hand, the sheathed nanowires are formed at SnO2 to Bi2O3 weight ratios above 4:1. The nanowires have only tetragonal Sn19Bi structure with a diameter of approximately 100 nm. Elementary analyses support the core/shell heterostructure of the resulting products. A favorable temperature for the Sn-rich Sn19Bi nanowires is in the range of 700–800 °C, more specifically around 750 °C. Thermodynamic analysis reveals that the CNTs play a significant role in the protection of the Bi–Sn nanostructures during phase transition by temperature change. This simple and reproducible method may be extended to the fabrication of similar binary or ternary nanostructures.

When operating reverse electrodialysis (RED) with several hundreds of cell pairs, a large stack voltage of more than 10 V facilitates water electrolysis, even when redox couples are employed for the electrode reaction. Upon feeding natural water containing multivalent ions, ion crossover through a shielding membrane causes inorganic scaling around the cathode and the interior of the membrane stack, due to the combination with the hydroxide ions produced via water reduction. In this work, we introduce a bipolar membrane (BPM) as a shielding membrane at the cathode to suppress inorganic precipitation. Water splitting in the bilayer structure of the BPM can block the ions diffusing from the catholyte and the feed solution, maintaining the current density. To evaluate the effect of the BPM on the inorganic precipitates, diluted sea salt solution is allowed to flow through the outermost feed channel near the cathode, in order to maintain as large a stack voltage as possible, which is important to induce water splitting in the BPM when incorporated into an RED stack of 100 cell pairs. We measure the electric power of the RED according to the arrangement of the BPM and compare it with that of conventional RED. The degree of inorganic scaling is also compared according to the kind of shielding membrane used (anion exchange membrane, cation exchange membrane, and BPM (Neosepta or Fumasep)). The BPM (Neosepta) shows the best performance for suppressing the formation of precipitates. It can hence be used to design a highly stable electrode system for long-term operation of a large-scale RED feeding natural water.

We report the synthesis of carbon-encapsulating carbonate apatite nanowires through vapor–solid growth by heat-treatment of biomass comprising calcium compounds such as CaC2O4 or CaCO3 at 900 °C using both PH3 and C2H2 as the reactants. The thermal decomposition of CaC2O4 or CaCO3 to CaO with increasing temperature (CaC2O4 → CaCO3 + CO → CaO + CO2) is the key to achieving the growth of such core–shell nanowires. First, vapor-phase reactions between the gaseous calcium species generated from the derived CaO and gaseous molecules derived from thermal reactions of the reactants (PH3 and C2H2) lead to the oriented growth of core–shell nanowires along the [001] plane. Second, the CO2 generated during the decomposition of CaCO3 may be primarily responsible for the incorporation of carbonate ions into the apatite structure. Nanowire growth with knots along the growth direction reveals that our approach is very controllable. Additional demonstrations using kenaf fibers further verify that other types of biomass too are usable.