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Recently, several three-dimensional (3D) bioprinting techniques have emerged for the synthesis of 3D tissue analogs. Accordingly, many researchers have focused on the development of novel bioinks that can mimic the natural extracellular matrix with cytocompatibility and biofunctionality. Hyaluronic acid and collagen are the most abundant proteins in the extracellular matrix of the skin and are known to support several cellular behaviors. Herein, we developed tyramine-conjugated hyaluronic acid and collagen (HA-Tyr/Col-Tyr) hydrogel bioinks, which are photocrosslinkable in the presence of riboflavin and ammonium peroxydisulfate, to fabricate dermis-mimetic constructs. The physicochemical properties and 3D printability of the HA-Tyr/Col-Tyr hydrogel were examined. 3D printing of the lattice structure with the HA-Tyr/Col-Tyr hydrogel enabled a sophisticated micron-sized fine structure without any clogging or coagulation. Approximately 80% of normal human dermal fibroblasts (NHDFs) in the printed constructs were alive after 24 h of culture. Moreover, the 3D printed constructs supported 4.57-fold cell proliferation and 4.23-fold f-actin expansion over four days in culture, indicating that HA-Tyr/Col-Tyr hydrogels provide cytocompatible microenvironments. The findings of this study suggest that HA-Tyr/Col-Tyr hydrogels are promising candidates as bioinks for the 3D printing of dermis-mimetic constructs.

Polymer gel electrolytes (PGEs) have been extensively studied and used in various electrochemical applications such as lithium secondary batteries and dye-sensitized solar cells (DSC) because of their suitable ionic conductivity and high physical stability. The PGEs should be easily injected into the electrochemical cells to replace the liquid electrolyte and maintain a high ionic conductivity over a wide temperature range. Therefore, in this study, the rheological properties of PGEs have been appropriately controlled by employing various polymer materials derived from poly(ethylene oxide) (PEO). The optimal PGE composition exhibiting both excellent ion conductivity and electrochemical stability has been determined by investigating the combination of various polymer materials including special functional groups and with various glass transition temperatures and molecular weights. In particular, the PEO-based PGEs developed in this study have the advantage of being easy to inject at room temperature and maintaining physical stability and ionic conductivity at a wide temperature with the help of a thermoreponsive behavior of the polymer material selected in this work. The prepared PEO-based PGEs have been evaluated by application to various electrochemical cells such as lithium secondary batteries, dye-sensitized solar cells, and electrochromic devices. The detailed results will be presented and discussed at the conference. This work was financially supported by the Environmental Industry Advancement Technology Development Project of Korea Environmental Industry & Technology (KEITI) funded by Korea Ministry of Environment (MOE) (No. 2017000140002/ RE201702218).

Recently, the interest in high-performance energy storage system (ESS) is increasing since it is a very essential part of the smart grid for stable and efficient electricity supply. At present, diverse battery technologies such as lithium ion batteries, redox flow batteries (RFBs), and sodium–sulfur batteries are competing with each other to be applied to commercial ESS. Among them, RFBs are considered to be the most promising for a large-scale ESS application. Meanwhile, all-vanadium redox flow batteries (VRBs) utilizing vanadium ions in different oxidation states as the active redox species have been considered as one of the most promising RFBs owing to the controlled crossover rate of the redox species through membranes. Since an ionomer membrane separator is one of the most dominant components determining the charge-discharge characteristics of RFB systems, the development of highly efficient membranes has been considered to be very essential for successful commercialization of VRBs. Among various kinds of membranes, pore-filled ion-exchange membranes (PFIEMs) fabricated by combining a porous substrate and an ionomer are known to have excellent characteristics including high chemical and dimensional stabilities, low manufacturing cost, low mass transfer resistance, etc. In this work, we have developed novel PFIEMs by using a polyethylene (PE)- or a polytetrafluoroethylene (PTFE)-based porous substrate for VRB applications. Especially, we have designed the filling ionomer to possess the high crosslinking degree and ion-exchange capacity, simultaneously. In addition, the prepared PFIEMs and the RFB employing them have been systematically analyzed by various electrochemical methods for evaluating their performances exactly. The detailed results will be presented and discussed at the conference. This work was supported by a grant (No.2017000140002/ RE201702218) from the Environmental Industry Advancement Technology Development Project of Korea Environmental Industry & Technology funded by Korea Ministry of Environment.

An electrolyte is one of the essential components in diverse electrochemical devices including lithium secondary batteries and dye-sensitized solar cells (DSSCs). Traditional liquid electrolytes having a high ion conductivity suffer from a problem of lowering the durability of the electrochemical devices because they have high flowability and volatility. Therefore, to improve the reliability of the electrochemical devices, it is preferable to replace the liquid electrolyte with a quasi-solid electrolyte. However, quasi-solid electrolytes are usually difficult to inject the devices and have a lower ion conductivity due to a higher viscosity than liquid electrolyte. In this study, we have developed a quasi-solid electrolyte which is based on a low molecular weight gelator (LMWG) with high conductivity and stability through proper physical crosslinking. In addition, the combination of various polymer materials including special functional groups with LMWG has been investigated for the optimization of the electrolyte performances. Especially, the prepared quasi-solid electrolytes have been systematically analyzed by various electrochemical methods and applied to both lithium battery and DSSC for evaluating their performances. The detailed results will be presented and discussed at the conference. This work was supported by a grant (No.2017000140002/ RE201702218) from the Environmental Industry Advancement Technology Development Project of Korea Environmental Industry & Technology funded by Korea Ministry of Environment.

Compared to fuel cells using proton exchangeable polymers, the direction of ion movement in the fuel cells using anion conducting polymer membranes shown in Figure 1 is opposite which is from cathode to anode. The hydroxyl ion movement mitigates overpotential for oxygen reduction reaction as well as water flooding at cathode. In addition, they overcome the disadvantages of alkaline fuel cells such as formation of carbonate precipitates, leakage of liquid KOH electrolyte, system complexity and so on by using solid electrolytes. Anion conducting ionomers are the polymers where anion exchangeable fixed groups, e.g., quaternary ammonium groups, are covalently attached to main backbones. It conducts the selective movement of anions which is allowed to be transported inside free volume of wet polymers. Much efforts are devoted to the development of anion conducting membranes as electrolytes of the fuel cell, but few researches on ionomer binder solutions for preparation of electrodes of membrane-electrode assemblies were carried out due to the technical difficulty in dispersing the polymers in various solvent systems. In this study, poly(phenylene oxide) (PPO) were brominated and in-situ quaternized by trimethyl ammonium during membrane casting. Once it was cast, it was hardly dispersed in any solvent system. Thus, the polymer was frozen by aqueous nitrogen and was ground by a blade-type grinder. Upon grinding time, the final forms were powders with different size of particle. The powder was used to prepare ionomer binder solutions, and the solutions (or dispersions) were characterized in terms of ion conductivity, ion exchange capacity, FT-IR, dynamic light scattering. In addition, the performance of membrane-electrode assemblies with the content of the ionomer with respect to I-V polarization, cyclic voltammetry, and impedance. Acknowledgment This work was supported by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning(KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20153030031720).

Ion exchange membranes (IEMs) have been widely employed in various water treatment processes such as electrodialysis for a desalination of sea or brackish water. Recently, they have also gained increased industrial importance in the applications to electrochemical energy conversion and storage processes such as reverse electrodialysis, fuel cells, and redox flow batteries. Their intrinsic properties such as electrical resistance and permselectivity are the key parameters dominating the electrochemical energy conversion efficiencies. The cost-effectiveness of ion-exchange membranes should also be considered for successful commercialization of the IEM process. In recent years, pore-filled IEMs (PFIEMs) in which an inert porous substrate provides excellent mechanical and chemical stabilities while a filling ionomer selectively transports ions through the membrane have been receiving great interests in the application to various separation and energy processes. In this work, we have investigated the optimum design parameters of the cost-effective PFIEMs for successful application to various IEM processes. In more detail, novel PFIEMs were successfully fabricated by combining a highly porous polymer (i.e. PTFE and PE) films and cationic polyelectrolytes with structurally stable anion-exchange sites for the applications to alkaline direct liquid fuel cells, all vanadium redox flow battery, and reverse electrodialysis. The prepared PFIEMs exhibited excellent electrochemical characteristics and stabilities and also remarkable energy conversion efficiencies have been achieved by employing them. Acknowledgments: This work was supported in part by the New & Renewable Energy Core Technology Program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (20153030031720) and the Technology Innovation Program funded by the Korea government (MOTIE) (No. 10047796).

Light-emitting device based electrochemiluminescent (ECL) process promises cost-efficient, large-area emissive applications, as its electrochemical characteristic enables use of air-stabile electrodes and single-layered emitting material. However, rapid degradation of its performance along with thermal decomposition of the device has proven a seemingly fundamental problem. Herein, we present a novel approach that overcomes this critical issue showing that the pulsed current operation regarding electrochemical redox kinetics on the surface of electrode should be considered in order to minimize undesired side reactions. By designing and operating solution-based ECL devices, we confirm the basic principles and conditions for stable performance of the ECL device. It is also demonstrated that applying a controlled-current pulse instead of controlled-voltage yields enhanced stability of ECL devices yielding a half-life time for > 2,000 sec. Bis (2-phenylquinoline) iridium (III) picolinic acid was employed as an ECL luminophore, and the devices were analyzed under various operating conditions; controlled-voltage or controlled-current pulses were applied to the device at different magnitude, frequency, and duty cycle.

There has been much attention towards dye-sensitized solar cells (DSSCs) for the past decades due to their attractive features such as high energy conversion efficiency and low production cost etc. Recently, cobalt complexes have been suggested as one of the most promising candidates for replacing conventional iodine redox couples owing to their high voltage characteristics. Even though respectable energy efficiency exceeding 12% was reported by employing liquid electrolyte that consists of cobalt complex redox mediator and volatile solvent, the use of volatile liquid solvent cannot ensure the long-term stability of DSSCs. In this work, therefore, novel polymer gel electrolytes (PGEs) including cobalt complexes as redox couples have been prepared for efficient and long-term stable DSSCs. In addition, several ways to mitigate the charge recombination rate at the interface between PGE and photoanode have been systematically investigated. The electron transport properties in mesoporous TiO2 electrodes (i.e. electron lifetime and diffusion coefficients) have been evaluated through IMPS and IMVS analyses. In addition, the photovoltaic performances of DSSCs employing prepared PGEs have been evaluated via the J-V curve measurements and various electrochemical characterizations. Acknowledgments: This work was supported by a grant (No.2017000140002/ RE201702218) from the Environmental Industry Advancement Technology Development Project of Korea Environmental Industry & Technology (KEITI) funded by Korea Ministry of Environment (MOE).

Polymer gel electrolytes (PGEs) have been widely investigated and utilized in various electrochemical applications such as lithium secondary batteries and dye-sensitized solar cells because they possess moderate ion conductivity and high physical stability. They have also been developed for the application to electrochromic devices (ECDs). Recently, ECDs have been attracting much attention owing to their use as a smart window. A smart window or a smart glass can effectively control the light transmission properties for the purpose of proper lighting or heating etc. The PGEs as one of the key components of the ECDs can dominate the major characteristics of transmittance and colored time etc. Especially, the ion conductivity and volatility of the PGEs should be optimized for the fabrication of efficient and durable ECDs. In addition, efficient injection process of highly viscous PGEs during the fabrication of large area ECDs should also be considered. In this work, therefore, we have developed the PGEs which can be easily loaded as a film and then in-situ polymerized through UV irradiation. The PGEs have also been applied to photoelectrochemical cells (i.e. dye-sensitized solar cells) for the efficient energy harvesting from solar irradiation. Acknowledgments: This work was supported by a grant (No.2017000140002/ RE201702218) from the Environmental Industry Advancement Technology Development Project of Korea Environmental Industry & Technology (KEITI) funded by Korea Ministry of Environment (MOE).

Reverse electrodialysis (RED) represents an energy conversion technology from the salinity difference of concentrated salt solutions (e.g., sea water) and diluted salt solutions (e.g., river water). The RED stack is comprised of an alternating arrangement of cation- and anion-exchange membranes between two electrodes that selectively transfer anions and cations. However, the river water used for the RED may contain natural organic matters (i.e., humic acid and fulvic acid). Thus, electrostatic characteristics of organic matter may lead to membrane surface fouling. The membrane fouling cause increase electrical resistance and the increase of maintenance cost, and a significant decrease in operating performance. In this study, the influence of membrane fouling in RED by commercially available humic acid was investigated experimentally, and adsorption tests, open circuit voltage, stack resistance, and power density were measured at different operation conditions. As a result, it was confirmed that the adsorption of humic acid onto the surface of anion-exchange membranes occurred even though the direction of the electromigration of negatively charged humic acid was toward cation-exchange membranes. The fouling of anion exchange membranes by humic acid was highly influenced by the roughness of the surface of anion-exchange membranes. It was confirmed by isothermal curves (i.e., Frendlich isotherm). Acknowledgements This work was supported by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, and Republic of Korea (No. 20143030071240).

Ion selective polymers (ionomers) are currently widely used in water treatment applications such as the diffusion dialysis, electrodialysis, and capacitive deionization for the desalination of brackish water, production of table salt, recovery of valuable metals from the effluents of metal-plating industry, and recoveries of acid and base from the spent leaching solutions. The functional ionomers are also utilized in various energy devices such as polymer electrolyte membrane fuel cells, redox flow batteries and so on. Especially, capacitive deionization (CDI) is thought to be one of the attractive environmentally-friendly desalination processes. It consumes relatively small energy for operation compared with other competing processes such as reverse osmosis. In addition, it does not produce any secondary regeneration wastes for a re-use. Comparing to the conventional CDI, membrane-CDI (MCDI) and ionomer coated-CDI have gained great interests due to the higher ion selectivity and removal efficiency. In this work, therefore, we have synthesized and characterized functional ionomers for the successful CDI application. The anion-exchange polymer was made from poly(2,6-dimethyl-1,4-phenylene oxide) through the bromination and consecutive amination processes. Meanwhile, the cation-exchange polymer was prepared via the sulfonation of polyetheretherketon. The functionalized ionomers exhibited excellent electrochemical properties of both the low electrical resistance and high ion selectivity. As a result, the functionalized ionomers which were coated on porous carbon electrodes largely improved the current and salt removal efficiencies of the CDI process. We have also developed a pore-filled IEMs (PFIEMs) for the applications to cost and energy efficient CDI processes. The PFIEMs composed of a highly inert and tough porous substrate and a polymer with functional groups that fills the pores can provide both high ion conductivity and excellent mechanical properties. In addition, the PFIEMs could be produced in a cheaper way by a roll-to-roll continuous process. The PFIEMs with a film thickness below 50 μm have been successfully prepared and characterized via various electrochemical analyses. As a result, they were shown to possess excellent electrochemical and mechanical properties. Their electrochemical characteristics have also been optimized for the successful applications to MCDI processes. (This work was supported by the Human Resource Training Program for Regional Innovation and Creativity through the Ministry of Education and National Research Foundation of Korea (NRF-2015H1C1A1034436) and also by the Technology Innovation Program funded by the Ministry of Trade, industry & Energy (MOTIE) (No. 10047796).)

There has been much attention towards dye-sensitized solar cells (DSSCs) for the past decades due to their attractive features such as reasonable energy conversion efficiency and low energy production cost. Even though a respectable energy conversion efficiency (~12%) has been achieved for photovoltaic cells employing organic liquid electrolyte that consists of I-/I3 - redox couples and volatile solvent (e.g. acetonitrile), the leakage and evaporation of liquid solvent from such cells has been suggested as the one of the critical factors limiting the long-term stability of the DSSC. Moreover, the use of I-/I3 - redox couples limits the energy conversion and even causes some problems such as the metal corrosion and visible light absorption etc. Recently, cobalt complexes (e.g. [Co(bpy)3]2+/3+, bpy=2,2’-bipyridine) have been suggested as one of the most promising candidates for replacing conventional I-/I3 - redox shuttles owing to their high voltage characteristics. Although a high energy efficiency exceeding 12% was reported by employing liquid electrolyte that consists of cobalt complex redox mediator and volatile solvent, the use of volatile liquid solvent cannot ensure the long-term stability of the DSSCs. In this work, therefore, novel quasi-solid electrolytes (QSEs) including cobalt complexes as redox couples have been developed for efficient and long-term stable DSSCs. The physicochemical properties of QSEs were adjusted by selecting proper solvent and functional additives (for improving cobalt complex solubility and cation transference number etc.). Polyethers with polar groups and polymers without polar groups were used as the polymer additives for the gelation of the liquid electrolytes with various blending ratios. The DSSC employing the QSEs showed the respectable energy conversion efficiency comparable with those of the DSSCs with liquid electrolytes. After the thermal aging tests, it was also proven that the long-term stability of the DSSC employing the QSE is much better than that of the cell filled with volatile liquid electrolyte. (This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Korea government (MSIP) (2015R1A1A1A05001486).)

Reverse electrodialysis (RED) represents an energy conversion technology from the salinity difference of concentrated salt solutions (e.g., sea water) and diluted salt solutions (e.g., river water). The RED stack is comprised of an alternating arrangement of cation- and anion-exchange membranes between two electrodes that selectively transfer anions and cations. However, the sea water used for the RED may contain the divalent cations (i.e., Ca2+ and Mg2+). Thus, electrostatic characteristics of divalent cations may lead to membrane surface fouling. The membrane fouling cause increase electrical resistance and the increase of maintenance cost, and a significant decrease in operating performance. In this study, the influence of membrane fouling in RED by divalent cations such as Ca2+ and Mg2+ was investigated experimentally, and equilibrium tests, open circuit voltage, stack resistance, and power density were measured at different operation conditions. Commercially available cation exchange membranes were used. As a result, the divalent ions behaved a reversible foulant to cation exchange membranes caused an increase in resistance. Calcium ion exchanged cation exchange membranes showed higher resistance than magnesium ion exchanged ones. It is also concluded that the number of hydration attached to cations greatly influenced resistance. Acknowledgements This work was supported by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, and Republic of Korea (No. 20143030071240).

Reverse electrodialysis (RED) is one of the promising processes for generating electricity from the salt concentration gradient between river and sea water. A RED stack contains alternately arranged anion- and cation-exchange membranes (AEMs and CEMs, respectively) which separate salt solutions of different concentrations. The power generation performance of REDs significantly depends on the characteristics of ion-exchange membranes (IEMs). The important membrane properties dominating the power generation in RED processes are the ion-exchange capacity, water swelling degree, electrical resistance, permselectivity, membrane thickness, and surface morphology etc. Moreover, the cost-effectiveness of IEMs is the most significant factor determining the successful commercialization of the RED process. In recent years, pore-filled IEMs (PFIEMs) in which an inert porous substrate provides excellent mechanical and chemical stabilities while a filling ionomer selectively transports ions through the membrane have been receiving great interests in the application to various energy conversion processes such as fuel cells and redox flow batteries. Simple and cheap mass production by a roll-to-roll process is one of the main advantages of the PFIEMs. In this work, we have investigated the optimum design parameters of the PFIEMs for successful application to a RED process. In addition, we have studied on the surface modification of the PFIEMs through facile methods for the improvement of the membrane properties. (This work was supported in part by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Korea government (MSIP) (2015R1A1A1A05001486) and the Technology Innovation Program funded by the Korea government (MOTIE) (No. 10047796).)

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