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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.

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.

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.

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.

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.

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.

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.

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 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.

We report the synthesis of carbon nanowires (CNWs) via chemical vapor deposition using catalytic decomposition of ethanol on nanosized transition metals such as Co, Fe, and Ni. Dip-coating process was used for the formation of catalytic nanoparticles, inducing the growth of CNWs on the surface of the carbon fiber paper (CFP). The liquid ethanol used as carbon source was atomized by an ultrasonic atomizer and subsequently flowed into the reactor that was heated up to a synthesis temperature of 600–700°C. Microscopic images show that CNWs of

This paper presents nano-sized carbon filaments grown by catalytic decomposition of ethanol on polycrystalline nickel foam. Our study is focused on the effects of synthesis conditions on the formation of filamentous carbon. The formation rate of filamentous carbon increased as the supply of liquid ethanol into the furnace and the synthesis time increased during growth process, whereas H 2 concentration in carrier gas had the opposite effect. The most favorable temperature for the highest formation rate was around 600 °C. We investigated the role of catalytic nanoparticles in the growth mechanism of filamentous carbon. Tip growth was the primary mechanism responsible for growth of the filamentous carbon; octopus-like carbon filaments were formed on large nanoparticles of about 100 nm in diameter. It was also discovered that surface break-up on the nickel foam precipitated the formation of filamentous carbon. We detected the presence of Ni 3 C as synthesis conditions after a long exposure to ethanol.

It has been known that single-strand DNA wraps around a single-walled carbon nanotube (SWNT) by pi-stacking. In this paper it is demonstrated that such DNA is dissociated from the SWNT by Watson-Crick base-pairing with a complementary sequence. Measurement of field effect transistor characteristics indicates a shift of the electrical properties as a result of this "unwrapping" event. We further confirm the suggested process through Raman spectroscopy and gel electrophoresis. Experimental results are verified in view of atomistic mechanisms with molecular dynamics simulations and binding energy analyses.