• Journal of Electrochemical Science and Technology
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• v.14 no.4
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• pp.388-396
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• 2023

Photoelectrochemical (PEC) water splitting is a vital source of clean and sustainable hydrogen energy. Moreover, the large-scale H₂ production is currently necessary, while long-term stability and high PEC activity still remain important issues. In this study, a GaN-based photoelectrode was modified by an additional NH₃ treatment (900℃ for 10 min) and its PEC behavior was monitored. The bare GaN exhibited a highly crystalline wurtzite structure with the (002) plane and the optical bandgap was approximately 3.2 eV. In comparison, the NH₃-treated GaN film exhibited slightly reduced crystallinity and a small improvement in light absorption, resulting from the lattice stress or cracks induced by the excessive N supply. The minor surface nanotexturing created more surface area, providing electroactive reacting sites. From the surface XPS analysis, the formation of an N-Ga-O phase on the surface region of the GaN film was confirmed, which suppressed the charge recombination process and the positive shift of E_FB. Therefore, these effects boosted the PEC activity of the NH₃-treated GaN film, with J values of approximately 0.35 and 0.78 mA·cm^-2 at 0.0 and 1.23 V_RHE, respectively, and an onset potential (V_on) of -0.24 V_RHE. In addition, there was an approximate 50% improvement in the J value within the highly applied potential region with a positive shift of V_on. This result could be explained by the increased nanotexturing on the surface structure, the newly formed defect/trap states correlated to the positive V_on shift, and the formation of a GaO_xN_1-x phase, which partially blocked the charge recombination reaction.

• Journal of Electrochemical Science and Technology
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• v.15 no.3
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• pp.405-413
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• 2024

Several techniques for determining the reverse peak current from a cyclic voltammogram (CV) for a reversible system are described in the literature: CV itself as a baseline with long switching potential (E_λ) that serves as a baseline for other CVs, Nicholson equation that uses CV parameters to calculation reverse peak current and linear extrapolation of the current obtained at the switching potential. All methods either present experimental difficulties or large errors in the peak current determination. The paper demonstrates, both theoretically and experimentally, that trapezoidal cyclic voltammetry (TCV) can be used as a baseline to determine anodic peak current (i_ap) with high accuracy and with a switching potential shorter than that used by CV, as long as E_λ is at least 130 mV away from the cathodic peak. Beyond this value of switching potential the electroactive specie is completely depleted from the electrode surface. Using TCV with E_λ = 0.34 V and a switching time (t_λ) of 240 s as a baseline, the determination of the reverse peak current presents a deviation from the expected value of less than 1% for most of the CVs studied (except cases when E_λ is close to the direct potential peak). This result presents better accuracy than the Nicholson equation and the linear extrapolation of the current measured at the switching potential, in addition to presenting a smaller error than that obtained in the acquisition of the experimental current. Furthermore, determining the reverse peak current by extrapolating the linear fit of i_ap vs. ${\sqrt[1/]{t_{\lambda}}}$ to infinite time gave a reasonable approximation to the expected value. Experiments with aqueous potassium hexacyanoferrate (II) and ferrocene in acetonitrile confirmed the theoretical predictions.

• Composites Research
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• v.37 no.4
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• pp.247-264
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• 2024

Recent advances in electro-active polymer (EAP) actuators, owing to their flexibility, lightweight, and simple fabrication process, have showcased their high utility across various fields such as soft robotics, biomimetics, wearable devices, and haptic technologies. Moreover, EAP actuators are evolving into smart devices with new functions and characteristics through the integration of functional materials and innovative technologies. This paper categorizes EAPs into ionic EAPs and electronic EAPs. Ionic EAPs include, most notably, ionic polymer-metal composites (IPMCs) and conducting polymers (CPs), while electronic EAPs encompass dielectric elastomer actuators (DEAs), ferroelectric polymer actuators, and the recently introduced hydraulically amplified self-healing electrostatic (HASEL) actuators. Detailed explanations based on the latest research are provided concerning the mechanism, structure, performance improvement strategies, methods for adding functionality, and application areas for each type of actuator.

• Journal of the Korean Electrochemical Society
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• v.19 no.1
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• pp.21-27
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• 2016

Vanadium redox flow batteries (VRFBs) using the electrolytes containing various vanadium ions in sulfuric acid as supporting solution are one of the energy storage devices in alternatively charging and discharging operation modes. The positive electrolyte contains $V^{5+}/V^{4+}$ and the negative electrolyte $V^{2+}/V^{3+}$ depending on the operation mode. To prevent the mixing of two solutions, proton exchange membranes are mainly used in VRFBs. Nafion 117 could be the most promising candidate due to the strong oxidative property of $V^{5+}$ ion, but causes high crossover of electroactive species to result in a decrease in coulombic efficiency. In this study, the composite membranes using Nafion ionomer and porous polyethylene substrate were prepared to keep good chemical stability and to decrease the cost of membranes, and were compared to the properties and performance of the commercially available electrolyte membrane, Nafion 117. As a result, the water uptake and ionic conductivity of the composite membranes increased as the thickness of the composite membranes increased, but those of Nafion 117 slightly decreased. The permeability of vanadium ions for the composite membranes significantly decreased compared to that for Nafion 117. In a single cell test for the composite membranes, the voltage efficiency decreased and the coulombic efficiency increased, finally resulting in the similar energy efficiency. In conclusion, the less cost of the composite membranes by decreasing 6.4 wt.% of the amount of perfluorinated sulfonic acid polymer due to the introduction of porous substrate and lower vanadium ion permeability to decrease self-discharge were achieved than Nafion 117.

• Applied Chemistry for Engineering
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• v.30 no.6
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• pp.698-706
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• 2019

Over the last few decades, there have been a lot of efforts to develop soft actuators, which can be external stimuli-responsive and applied to the human body. In order to fabricate medical soft actuators with a dynamic precision control, the 3D crosslinked poly(acrylic acid) (PAAc)/poly(vinyl alcohol) (PVA)/poly(ethylene glycol) (PEG) hydrogels were synthesized in this study by using a radiation technique without noxious chemical additives or initiators. After irradiation, all hydrogels showed high gel fraction over 75% and the ATR-FTIR spectra indicated that PAAc/PVA/PEG hydrogels were successfully synthesized. In addition, the gel fraction, equilibrium water content, and compressive strength were measured to determine the change in physical properties of PAAc/PVA/PEG hydrogels according to the irradiation dose and content ratio of constituents. As the irradiation dose and amount of poly(ethylene glycol) diacrylate (PEGDA) increased, the PAAc/PVA/PEG hydrogels showed a high crosslinking density and mechanical strength. It was also confirmed that PAAc/PVA/PEG hydrogels responded to electrical stimulation even at a low voltage of 3 V. The bending behavior of hydrogels under an electric field can be controlled by changing the crosslinking density, ionic group content, applied voltage, and ionic strength of swelling solution.

• Polymer(Korea)
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• v.25 no.1
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• pp.6-14
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• 2001

The monomer N,N'-bis(3-pyrrol-1-yl-propyl)-4,4'-bipyridinium$(PF_6)_2$ was electrochemically polymerized on glassy carbon electrode surface. This polymer film electrode has electroactive sites on its bipyridinium ions distributed at the polymer strands. The formal potentials of the electrodes were -0.41V and -0.81V(vs. SSCE) for each step at phosphate buffer(pH=5.70). The diffusion coefficients of the dopants ions into the polymer matrix were $1.57{\times}10^{-4}$ and $4.35{\times}10^{-5}cm^2s^{-1}$ for first and second redox couple, respectively. The rate constants of electron transfer at $V^{2+/+}$ of the first step was a $57.53s^{-1}$, which was 22 times higher than $V^{+/0}$ one having $2.63s^{-1}$ in the solution. The charge transfer resistance of the polymer film was influenced by the dopant ion of the electrolyte. Thus the resistances were 22.63, 16.81, 12.44 and $11.36k{\Omega}$ for $LiClO_4,\;NaClO_4,\;KClO_4$, and phosphate buffer, respectively. The reaction order of the electropolymerization was first order and the rate constant of the polymerization was $1.31{\times}10^{-1}s^{-1}$ as determined by EQCM method. The G.C./p-BPB type electrode doped with phosphate ions showed a stability and reproducibility in CV procedure over 20 cycles.

• Applied Biological Chemistry
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• v.47 no.3
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• pp.300-306
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• 2004

Eight cation or anion-responsive polymer membranes were prepared by a casting procedure employing polyvinyl chloride, Bis (2-ethylhexyl)sebacate and each electroactive material in the ratio of 66 : 33 : 1. The resulting membranes were separately installed onto the sensitive area of the ionic electrodes to produce an 8-channel taste sensor array. The taste sensors of the array were connected to a high-input impedance amplifier and the amplified sensor signals were interfaced to a PC via an A/D converter. The taste evaluation system was applied to a discriminant analysis on six groups of marketed beverages like sikhye, sujunggwa, tangerine juice, ume juice, ionic drink and green tea. When the signal data from the sensor array were analyzed by principal component analysis after normalization, the 1st, 2nd and 3rd principal component explained most of the total data variance. The six groups of the analyzed beverages were discriminated well in the three dimensional principal component space. The half of the five groups of the analyzed beverages was also discriminated in the two dimensional principal component plane.