수전해 시스템에서 제어되지 않은 수소 크로스오버(hydrogen crossover)는 효율 저하 및 폭발 위험성 등을 야기시 키는 위험 요인이다. 수전해 공정에서 양이온교환막(cation exchange membrane, CEM)은 완전히 수화된 상태로 운전되기 때 문에 이중상(two-phase) 물질로 취급하는 것이 중요하다. 본 총설에서는 수소 크로스오버의 특성 평가 중 발생할 수 있는 주 요 기술적 문제를 요약하였다. 특히, pressure decay method (PDM)는 수소 크로스오버를 정확하게 측정하기 위한 기법으로 평가되며, 막 내부 구조 분석에도 활용할 수 있다. 또한, 수소 크로스오버를 평가하는 데 있어 permeability (즉, 고유 물질 특 성) 차원의 고유한 한계를 논의하고, 공정 안전성을 위해 flux 기반(즉, 공정 파라미터)으로의 전환 필요성을 강조한다. 추가 적으로, 막-촉매 계면에서의 과포화(supersaturation) 현상이 크로스오버에 미치는 영향에 대한 연구 필요성을 강조한다.

Hydrogen isotope separation involves the separation of hydrogen, deuterium, tritium, and their isotopologues. It is an essential technology for removing radioactive tritium contamination and for obtaining valuable hydrogen isotope resources. Among various hydrogen isotope separation technologies, water electrolysis technology exhibits a high separation factor. Consequently, the electrolysis of tritiated water is of paramount importance as a tritium enrichment method for treating tritium-contaminated water and for analyzing tritium in environmental samples. More recently, hydroelectrolysis technology, which utilizes proton exchange membranes (PEM) to reduce water inventory, has gained favor over traditional alkaline hydroelectrolysis. Nevertheless, it is crucial to decrease the hydrogen permeability of the PEM in order to mitigate the explosion risk associated with tritium hydrogen electrolysis devices. Additionally, efforts are needed to enhance the hydrogen isotope selectivity of the PEM and optimize the manufacturing process of the membrane-electrode assembly (MEA), thereby improving both hydrogen isotope separation performance and water electrolysis efficiency. In this presentation, we will delve into two key aspects. Firstly, we’ll explore the reduction of hydrogen permeability and the enhancement of the hydrogen isotope separation factor in PEM through the incorporation of 2D nanomaterial additives. Secondly, we’ll examine the influence of various MEAs preparation methods on electrolysis and isotope separation performances. Lastly, we will discuss the effectiveness of the developed system in separating deuterium and tritium.

The separation of hydrogen isotopes is a critical issue in various fields, such as deuterium or tritium production and the treatment of radioactively contaminated water. In this presentation, we describe the pervaporative separation of hydrogen isotopes using proton conductive membranes and underlying separation mechanism. We investigated the H/D separation factors of perfluorosulfonic acid (Nafion) and polybenzimidazole membranes using pervaporation, and found that both membranes exhibited similar separation factors of approximately 1.026. Water permeation flux through the membranes was highly dependent on their thickness and type, and increased with operation temperature. However, the effect of temperature on H/D separation factor was negligible. We also demonstrated the cascade separation of H/D, indicating the potential application of multi-stage operation. We found that surface transport mechanisms such as hydron hopping contributed the most to H/D separation during the pervaporation process of proton conductive membranes.

Water electrolysis holds great potential as a method for producing renewable hydrogen fuel at large-scale, and to replace the fossil fuels responsible for greenhouse gases emissions and global climate change. To reduce the cost of hydrogen and make it competitive against fossil fuels, the efficiency of green hydrogen production should be maximized. This requires superior electrocatalysts to reduce the reaction energy barriers. The development of catalytic materials has mostly relied on empirical, trial-and-error methods because of the complicated, multidimensional, and dynamic nature of catalysis, requiring significant time and effort to find optimized multicomponent catalysts under a variety of reaction conditions. The ultimate goal for all researchers in the materials science and engineering field is the rational and efficient design of materials with desired performance. Discovering and understanding new catalysts with desired properties is at the heart of materials science research. This process can benefit from machine learning (ML), given the complex nature of catalytic reactions and vast range of candidate materials. This review summarizes recent achievements in catalysts discovery for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The basic concepts of ML algorithms and practical guides for materials scientists are also demonstrated. The challenges and strategies of applying ML are discussed, which should be collaboratively addressed by materials scientists and ML communities. The ultimate integration of ML in catalyst development is expected to accelerate the design, discovery, optimization, and interpretation of superior electrocatalysts, to realize a carbon-free ecosystem based on green hydrogen.

Water electrolysis is an efficient method to enrich heavy hydrogen isotopes (tritium and deuterium) in the aqueous phase. Although an alkaline water electrolyzer has been commercialized for mass production of hydrogen, such a method requires additional purification steps to remove electrolytes from the final concentrates. On the other hand, proton exchange membrane water electrolysis (PEMWE) does not require additional electrolyte treatment steps, and PEMWE is operated at higher current density compared to the alkaline water electrolysis. In this study, we investigated deuterium and tritium separation from light water by PEMWE. Separation behaviors at the anode and cathode were analyzed, and H/D and H/T separation factors were compared.

본 연구는 플라즈마 발생 장치를 수경재배 시스템과 결합하여 상추를 재배하고 수확 후 플라즈마 활성수와 과산화수소 0, 3, 6% 농도에 침지 처리를 하여 생육량 및 바이오 활성 물질 함량을 비교하였다. 고농도의 과산화수소로 인하여 근권부 생체중이 저해되는 결과를 나타냈으며, 엽장과 근권부 생체중을 제외하고는 유의적 차이가 발생하지 않았다. 상추 지상부의 chlorogenic acid와 4-hydroxy3-benzoic acid, 4-hydroxy benzoic acid 그리고 지상부 총 페놀 함량은 과산화수소 6%에 서 유의적으로 가장 높았다. 하지만 근권부에서 측정된 이차 대사산물인 quercetin 및 근권부 총 페놀 함량은 과산화수소 처리구보다 플라즈마 활성수에서 유의하게 높았다. 과산화수소 처리 기간 동안 상추의 뿌리는 직접적인 피해를 받으며 괴사하였으나, 잎에서는 과산화수소 6% 처리에서 바이오 활성 물질이 증가하는 결과를 나타내었다. 플라즈마 활성수 처리 상추는 생리 장해가 발생하지 않았으며, 과산화수소 6% 처리와 유사한 양의 이차대사산물 증대 효과를 나타내었다. 또한, 뿌리의 바이오 활성 물질 함량이 가장 높았던 결과 등을 고려 할 때 근채류 및 엽채류의 수경재배에 플라즈마 기술을 적용할 시 작물의 바이오 활성 물질 함량을 증대시키는 데 효과적일 것으로 판단된다.

수소는 산업용 전력생산, 자동차용 연료 등을 위한 대체가능한 에너지 담체로 인식되고 있다. 미래 저탄소 에너지 시스템에서 에너지 저장은 전력 수요에 유연하지 않거나 간헐적인 공급의 균형을 이루기 위한 중추적인 역할을 담당할 수 있 을 것이다. 수소는 에너지 담체로서 전기에너지를 화학에너지로, 화학에너지를 전기에너지로 변환할 수 있는 에너지 저장 방 법 중의 하나이다. 수소제조 방법 중에서, 특히, 물의 전기분해를 이용한 방법은 신재생 에너지원과의 접목을 고려할 때 가장 효율적이고 실용적인 방법으로 여겨지고 있다. 물 전기분해 수소제조 기술은 전기를 이용하여 수소를 물로부터 직접 제조하 는 방법으로, 화석연료 이용 제조방법과 비교하여 수소를 제조할 때 지구환경 오염물질인 이산화탄소의 배출이 없다. 수소제 조 방법 중의 하나인 물 전기분해의 원리와 물 전기분해의 종류인 알칼리 수전해(AWE, alkaline water electrolysis), 고분자 전해질막 수전해(PEMWE, polymer electrolyte membrane water electrolysis), 고온 수증기 전기분해(HTSE, high temperature steam electrolysis)에 대하여 분석하고자 하였다. 물 전기분해는 수소제조 방법의 하나로 연구가 진행되고 있으며, 최근에는 PTG (power to gas)와 PTL (power to liquid) 시스템의 요소기술로도 주목을 받고 있다. 본 총설에서는 물 전기분해에 대한 원리와 종류, 특히 알칼리 수전해에 대한 최근 연구동향에 대해 설명하였다.

화석연료 사용에 의한 환경문제의 해결을 위한 방법의 하나로 수소에너지에 대한 연구가 활발히 진행되고 있다. 물을 분해에 의한 수소 제조는 전기분해, 광화학적, 열화학적, 생물학적 방법 등이 있다. 물의 전기분해 기술은 전기를 이용하여 수소를 물로부터 직접 제조하는 방법으로 지구오염물질인 이산화탄소의 배출이 없는 것이 특징이다. 특히, 물의 전기분해 방법 중에서 알칼리 수전해는 오래전부터 알려진 수소제조 방법으로 전해액으로 ∼30 wt%의 KOH수용액 또는 ∼20 wt%의 NaOH수용액을 사용하며, 셀은 수산화이온 (OH-) 만을 선택적으로 통과시키는 격막, 수소와 산소를 발생시키는 전극으로 구성된다. 최근에는 양.음이온교환막의 발 전과 더불어 전해효율이 60% 이상에 이를 만큼 분리막의 중요성이 부각되고 있다.

Understanding effects of thermal pollution and acidification has long been a concern of aquatic ecologists, but it remains largely unknown in Korea. This study was performed to elucidate the effects of thermal wastewater effluent (TWE) and acid rain on water quality and attached algae in a small mountain stream, the Buso Stream, a tributary located in the Hantan River basin. A total of five study sites were selected in the upstream area including the inflowing point of hot-spring wastewater (HSW), one upstream site (BSU), and three sites below thermal effluent merged into the stream (1 m, 10 m and 300 m for BSD1, BSD2, and BSD3, respectively). Field surveys and laboratory analyses were carried out every month from December 2015 to September 2016. Water temperature ranged 1.7~28.8°C with a mean of 15.0°C among all sites. Due to the effect of thermal effluent, water temperature at HSW site was sustained at high level during the study period from 17.5°C (January) to 28.8°C (September) with a mean of 24.2±3.7°C, which was significantly higher than other sites. Thermal wastewater effluent also brought in high concentration of nutrients (N, P). The effect of TWE was particularly apparent during dry season and low temperature period (December~March). Temperature effect of TWE did not last toward downstream, while nutrient effect seemed to maintain in longer distance. pH ranged 5.1~8.4 with a mean of 6.9 among all sites during the study period. The pH decrease was attributed to seasonal acid rain and snow fall, and their effects was identified by acidophilic diatoms dominated mainly by Eunotia pectinalis and Tabellaria flocculosa during March and August. These findings indicated that water quality and periphyton assemblages in the upstream region of Buso Stream were affected by thermal pollution, eutrophication, and acidification, and their confounding effects were seasonally variable.

We report on the fabrication and characterization of a novel Cu2O/CuO heterojunction structure with CuO nanorods embedded in Cu2O thin film as an efficient photocathode for photoelectrochemical (PEC) solar water splitting. A CuO nanorod array was first prepared on an indium-tin-oxide-coated glass substrate via a seed-mediated hydrothermal synthesis method; then, a Cu2O thin film was electrodeposited onto the CuO nanorod array to form an oxide semiconductor heterostructure. The crystalline phases and morphologies of the heterojunction materials were examined using X-ray diffraction and scanning electron microscopy, as well as Raman scattering. The PEC properties of the fabricated Cu2O/CuO heterojunction photocathode were evaluated by photocurrent conversion efficiency measurements under white light illumination. From the observed PEC current density versus voltage (J-V) behavior, the Cu2O/CuO photocathode was found to exhibit negligible dark current and high photocurrent density, e.g. −1.05 mA/cm2 at −0.6 V vs. Hg/HgCl2 in 1 mM Na2SO4 electrolyte, revealing the effective operation of the oxide heterostructure. The photocurrent conversion efficiency of the Cu2O/CuO photocathode was estimated to be 1.27% at −0.6 V vs. Hg/HgCl2. Moreover, the PEC current density versus time (J-T) profile measured at −0.5 V vs. Hg/HgCl2 on the Cu2O/CuO photocathode indicated a 3-fold increase in the photocurrent density compared to that of a simple Cu2O thin film photocathode. The improved PEC performance was attributed to a certain synergistic effect of the bilayer heterostructure on the light absorption and electron-hole recombination processes.

The aim of this study was to evaluate the chemical quenching system for residual ozone and to determine the operating condition for the quenching system. Hydrogen peroxide (H₂O₂) and sodium thiosulfate (Na₂S₂O₃) were investigated as quenching reagents for ozone removal, and the tendency of each chemical was notably different. In the case of H₂O₂, the degradation rate of ozone was increased as the concentration of H₂O₂ increase, and temperature and pH value have a significant effect on the degradation rate of ozone. On the other hand, the degradation rate of ozone was not affected by the concentration of Na₂S₂O₃, temperature and pH value, due to the high reactivity between the S₂O₃²- and ozone. This study evaluates the decomposition mechanism of ozone by H₂O₂ and Na₂S₂O₃ with consideration for the water quality and reaction time. Furthermore, the removal test for the quenching reagents, which can be remained after reaction with ozone, was conducted by GAC process.

In this study, the reduction kinetics and behaviors of oxides in the water-atomized iron powder have been evaluated as a function of temperature ranging 850-1000˚C in hydrogen environment, and compared to the reduction behaviors of individual iron oxides including Fe2O3, Fe3O4 and FeO. The water-atomized iron powder contained a significant amount of iron oxides, mainly Fe3O4 and FeO, which were formed as a partially-continuous surface layer and an inner inclusion. During hydrogen reduction, a significant weight loss in the iron powder occurred in the initial stage of 10 min by the reduction of surface oxides, and then further reduction underwent slowly with increasing time. A higher temperature in the hydrogen reduction promoted a high purity of iron powder, but no significant change in the reduction occurred above 950˚C. Sequence reduction process by an alternating environment of hydrogen and inert gases effectively removed the oxide scale in the iron powder, which lowered reduction temperature and/or shortened reduction time.