Ho-Sang Choi

Preparation of anion exchange membrane using polyvinyl chloride (PVC) for alkaline water electrolysis

An anion exchange membrane was prepared by the chloromethylation and the amination of polyvinyl chloride (PVC), as the base polymer. The membrane properties of the prepared anion exchange membrane, including ionic conductivity, ion exchange capacity, and water content were measured. The ionic conductivity of the prepared anion exchange membrane was in the range of 0.098×10−2-7.0×10−2S cm−1. The ranges of ion exchange capacity and water content were 1.9-3.7meq./g-dry-membrane and 35.1-63.1%, respectively. The chemical stability of the prepared anion exchange membrane was tested by soaking in 30 wt% KOH solution to determine its availability as a separator in the alkaline water electrolysis. The ionic conductivity during the chemical stability test largely did not change.

Study on the Electrode Characteristics for the Alkaline Water Electrolysis

Alkaline electrolysis needs the electrode having a low overvoltage and good corrosion resistance in alkaline solution such as KOH and NaOH, for the oxygen and hydrogen production. The commercial materials such as SUS(stainless steel)-316, Ni and NiFe were evaluated for the electrode in alkaline electrolysis. The test solution for the alkaline electrolysis used 1~9M NaOH and 1~9M KOH. The voltage increased with an increase of current density in each solution. As for the 15wt.% (about 5M) NaOH, the voltage of the tested electrode under the current density of 1.8A/ showed the almost same value. The voltage over the current density of 1.8A/ deceased in the order: NiNiFe showed the almost same value. The voltage over the current density of 1.8A/ deceased in the order: NiFeSUS-316. From the results, it was estimated that NiFe and Ni was suitable as the electrode for the alkaline water electrolysis using NaOH and KOH electrolyte.

Dehydration through pervaporation from HIx solution (HI-H2O-I2 mixture) using a cation exchange membrane for thermochemical water-splitting iodine-sulfur process

Pervaporation (PV) of water from HIx solution (HI-H2O-I2 mixture) using Nafion-117 was evaluated aiming at the application to dehydrate the azeotropic composition in HI decomposition reaction of thermochemical IS process. PV experiment was carried out by using HI solutions of 40–65 wt% and an I2/HI molar ratio of 0–3 in the feed at the room temperature. The permeation flux decreased with increasing HI weight fraction in the feed. The permeation flux is dependent on the I2 concentration in the feed having an I2/HI molar ratio. A long time PV experiment was carried out using I2/HI molar ratio of 1 (in HI solution of 55.9%) in the feed at room temperature. It is expected that the permeation component in the permeate zone using the PV process was mainly H2O, and H2O permeation was constant with increasing operation time.

Study on the Electrolyte for Zn-Br Redox Flow Battery

Four types of electrolyte were tested for the application as an electrolyte in the Zn-Br redox flow battery. Electrolyte was consist of ZnBr2 (electrolyte number 1), ZnBr2+KCl (electrolyte number 2), ZnBr2 +KCl+NH4Br (electrolyte number 3) and ZnBr2+KCl+EMPBr(C7H16BF4N) (electrolyte number 4). The each electrolyte property was measured by CV (cyclic voltammetry) method. The different between the potential of anodic and cathodic maximum current density in a CV experiment (△EP) was 0.89V, 0.89V, 1.06V and 0.61V for the electrolyte number 1, 2, 3 and 4, respectively. The electrolyte involved KCl increased conductivity which was appeared by anodic and cathodic maximum current density in a CV experiment. It was estimated that the electrolyte of number 3 (ZnBr2+KCl+NH4Br) and number 4 (ZnBr2+KCl+EMPBr) could be suitable as an electrolyte in the Zn-Br redox flow battery with non-appeared bubble, non-Br formation and high anodic-cathodic maximum current density.

An Analysis on Stainless Steel for Hydrogen Generator' Pipeline Interacting with Alkaline Solution

This study was performed to observe the change of stainless steel pipe interacting with alkaline solution. We used STS316L and STS304 as samples which were soaked in alkaline solution. We measured the samples by use of FE-SEM, EDX, SIMS to observe the surface and depth profile of both samples. The result showed that the precipitate appeared on the surface of both samples from 5 days. but the precipitate was confirmed to be decreased as time passes. but the quantitative change of precipitates at both samples was different as time passed. The EDX showed that the precipitate is Potassium from solution of Electrolysis. The result also showed that the primary elements of stainless steel pipeline and of Alkaline Solution were changed. The change of primary elements was severe between 5 days to 16 days and was stable around 40 days at both samples. The reaction of STS316L with alkaline solution was lower than STS304. We hoped that this study would be the foundation of developing the electrode of the alkaline hydrogen generator.

Multiple tube preparation characteristics of silica hydrogen permselective membrane

The multiple tube preparation of a silica membrane using a porous α-alumina tube as a support tube was carried out by chemical vapor deposition (CVD) to scale up the membrane reactor. A porous alumina tube with a pore size of 100 nm was modified by chemical vapor deposition using tetraethoxysilane as an Si source. The single-component permeance of H2 and N2 in the prepared silica membrane that was achieved by a multiple tube membrane preparation system was measured at 300–600 °C. Hydrogen permeance of the modified membrane at a permeation temperature of 600 °C was 5×10−8 mol·Pa−1·m−2·s−1. H2/N2 selectivity at 600 °C was about 32. It was confirmed that permeance of H2 and N2 and the selectivity for H2 to N2 in the prepared silica membrane by the multiple tube membrane preparation system had almost the same value compared to those of the silica membrane prepared by the single-tube system.

Characteristics of the Zn-Br Redox Flow Battery using the Different Electrolyte and Membrane

>> Cell performance of the Zn-Br redox flow battery (ZBRFB) using two different type’s membrane (Nafion117 and SF-600) was evaluated at 20 mA/cm 2 of current density in 1M (mol/L) ZnBr2 + 2M KCl + 0.3M EMPBr(1-ethyl-1-methyl pyrrolidinium bromide) electrolyte. The average energy efficiencies of ZBRFB were 74.9% and 74.7% for Nafion117 and SF-600, respectively. The electrolyte added the 1-ethyl-3-methylimidazolium dicyanamide (EMICA) as an additive was tested for the electrolyte in ZBRFB using SF-600 at 30 mA/cm 2 of current density. An average energy efficiency of the ZBRFB was 74.5% and 77.4% for the electrolyte non-added EMICA and added 1wt% of EMICA, respectively. ZBRFB using the electrolyte added EMICA was showed the higher performance than that using the electrolyte non-added EMICA.

Analysis on Variation of Primary Elements of Stainless Steel Interacting with Alkali Solution

In this paper, We studied the change of surface and variation of elements on both electrodes of hydrogen generator of alkaline electrolysis in use of FE-SEM and SIMS. We used the stainless steel 316(600 ) as electrode in condition of 25%KOH, Temperature. The results show that the intensity of elements (C, Si, P, S, Ti, Cr, Mn, Fe, Ni, Mo) of Positive Electrode are decreased as much as about than the original electrode. Thickness of Positive Electrode is decreased about 40 after chemical reaction. The negative electrode, however, shows a slight variation in the intensity of elements (C, Si, P, Fe, Ni, Mn, Mo) but Change of thickness and surface` shape of electrode show nothing after chemical reaction. The change in thickness and variation of Stainless Steel 316 cause the lifetime of electrode to be shorted. We also observed hydrogen, oxygen, potassium in both electrodes. Especially, The potassium is increased in proportional with depth of positive electrode. this means the concentration of alkali solutions is changed. and so we have to supply alkaline solution to generator in order to produce same quantity of hydrogen gas continuously. we hope that this study gives a foundation to develop the electrode for hydrogen generator of alkaline electrolysis.

The Preparation Characteristics of Hydrogen Permselective Membrane for Higher Performance in Is Process of Nuclear Hydrogen Production

The thermochemical splitting of water has been proposed as a clean method for hydrogen production. The IS process is one of the thermochemical water splitting processes using iodine and sulfur as reaction agents. The silica membrane to apply for the HI decomposition membrane reactor of the IS process was prepared by sol-gel and thermal CVD methods.