• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.87.1-87.1
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• 2017

High functional catalyst to efficiently produce clean and earth-abundant renewable fuels plays a key role in securing energy sustainability and environmental protection of our society. Hydrogen has been considered as one of the most promising energy carrier as represented by focused research works on developing catalysts for the hydrogen evolution reaction (HER) from the water hydrolysis over the last several decades. So far, however, the major catalysts are expensive transition metals. Here using first principles density functional theory (DFT) calculations we screen various pyrites for HER by identifying fundamental descriptor governing the catalytic activity. We enable to capture a strong linearity between experimentally measured exchange current density in HER and calculated adsorption energy of hydrogen atom in the pyrites. The correlation implies that there is an underlying design principle tuning the catalytic activity of HER.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.77.4-78
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• 2016

Binary interactions may have significant impact on Pop III stellar evolution. Pop III single star evolution indicates that for primary masses less than $20M_{\odot}$, no significant binary mass transfer would occur before core helium exhaustion. We perform binary system evolution for various primary masses ($20M_{\odot}$ < $M_1$ < $60M_{\odot}$) and initial periods under same mass ratio $M_2/M_1=0.9$, and follow the evolution and mass transfer of the primary star. If binary mass transfer occurs during post main sequence, the primary star does not evolve into naked helium star and still contain significant hydrogen in the envelope. During the post mass transfer phase, the primary star evolves redward, and does not become sufficiently hot to enhance the number of ionizing photons, compared to the case of single star evolution for a given initial mass. This result implies that primary stars of massive Pop III binary systems would have little contribution to the reionization in the early universe. Given the large hydrogen content ($0.326-1.793M_{\odot}$), the primary stars that underwent stable mass transfers would explode as a Type IIb supernova, and it would be difficult for Pop III binary stars to produce Type Ib/c supernovae that look similar to those found in the local universe.

• Journal of the Korean Electrochemical Society
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• v.4 no.4
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• pp.166-171
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• 2001

In an aluminum-air unit cell used alkaline solution, Hydrogen evolution rates were investigated far the observation of the effects of alloy element, inhibitor and its concentration in electrolyte, KOH concentration, solution temperature, and current density loaded to cell. Hydrogen evolution rates were reduced up to $50\%$ by saturating the solution with ZnO, while ZnAc(Zinc Acetate) did not work as inhibitor. The inhibition effect of ZnO increased with increasing the KOH concentration and solution temperature. They were linearly increased with the KOH concentration and current density in first order and exponentially increased with the solution temperature.

• Applied Chemistry for Engineering
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• v.9 no.1
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• pp.52-57
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• 1998

The effects of additives such as zinc compounds in 4M KOH electrolyte of Al-air cell have been studied. Zinc compounds in electrolyte increased hydrogen evolution overpotential and TPC(tripotasium citrate)/CaO formed fine film on aluminum surface, and these additives decreased hydrogen evolution rate and corrosion rate of aluminum. These additives shifted the OCP in the positive direction on high purity aluminum(purity, 99.999%) and in the negative direction on Al No 1050(purity,99.5%). Addition of two or more additives resulted in the prevention or the reduction of corrosion rate and hydrogen evolution at OCP. As the overpotential on Al electrode increased, the hydrogen evolution rate decreased and the utilization of aluminum increased. At high current density$(>100mA/cm^2)$, TPC/CaO/ZnO additives increased the utilization of high purity aluminum up to that of aluminum alloys containing indium, gallium and thallium.

• Applied Chemistry for Engineering
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• v.34 no.6
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• pp.567-575
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• 2023

Water electrolysis is undergoing active research as one of the promising technologies for producing effective green hydrogen. Using seawater directly as a raw material for a water electrolysis system can solve the problem of the limitations of existing freshwater raw materials, as seawater accounts for approximately 97% of the water on Earth. At the same time, abundant by-product materials can be obtained, representative examples of which are Cl₂, ClO^-, Br₂, and Mg(OH)₂ produced during electrolysis, depending on their composition and pH environment. In order to develop a successful seawater electrolysis system and oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts, it is necessary to understand the causes and consequences of reactions that occur in the seawater environment. Therefore, in this paper, we will investigate the reaction mechanism and characteristics of the seawater electrolysis system as well as the research and development trends of electrochemical catalysts used in anode and cathode electrodes.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.1
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• pp.36-43
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• 2013

In this paper, a three-dimensional hydrogen desorption model is applied to a thin double-layered annulus ZrCo hydride bed and validated against the temperature evolution data measured by Kang et al. The present model reasonably captures the bed temperature evolution behavior and the 90% hydrogen discharging time. In addition, the performance of thin double-layered annulus bed is evaluated by comparing with a simple cylindrical bed using hydrogen desorption model. This study provides multi-dimensional contours such as temperature and H/M atomic ratio in the metal hydride region. This numerical study provides fundamental understanding during hydrogen desorption process and indicates that efficient design of the metal hydride bed is critical to achieve rapid hydrogen discharging performance. The present three-dimensional hydrogen desorption model is a useful tool for the optimization of bed design and operating conditions.

• Journal of the Korean institute of surface engineering
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• v.56 no.4
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• pp.243-249
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• 2023

Urea oxidation reaction (UOR) via electrochemical oxidation process can replace oxygen evolution reaction (OER) for green hydrogen production since UOR has lower thermodynamic potential (0.37 V_RHE) than that of OER (1.23 V_RHE). However, in the case of UOR, 6 electrons are required for the entire UOR. For this reason, the reaction rate is slower than OER, which requires 4 electrons. In addition, it is an important challenge to develop catalysts in which both oxidation reactions (UOR and OER) are active since the active sites of OER and UOR are opposite to each other. We prove that among the NiFe₂O₄ nanoparticles synthesized by the hydrothermal method at various synthesis temperatures, NiFe₂O₄ nanoparticle with properly controlled particle size and crystallinity can actively operate OER and UOR at the same time.

• Korean Journal of Materials Research
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• v.25 no.4
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• pp.191-195
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• 2015

To improve its textural properties as a support for platinum catalyst, carbon aerogel was chemically activated with KOH as a chemical agent. Carbon-supported platinum catalyst was subsequently prepared using the prepared carbon supports(carbon aerogel(CA), activated carbon aerogel(ACA), and commercial activated carbon(AC)) by an incipient wetness impregnation. The prepared carbon-supported platinum catalysts were applied to decalin dehydrogenation for hydrogen production. Both initial hydrogen evolution rate and total hydrogen evolution amount were increased in the order of Pt/CA < Pt/AC < Pt/ACA. This means that the chemical activation process served to improve the catalytic activity of carbon-supported platinum catalyst in this reaction. The high surface area and the well-developed mesoporous structure of activated carbon aerogel obtained from the activation process facilitated the high dispersion of platinum in the Pt/ACA catalyst. Therefore, it is concluded that the enhanced catalytic activity of Pt/ACA catalyst in decalin dehydrogenation was due to the high platinum surface area that originated from the high dispersion of platinum.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.42.4-43
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• 2020

The hydrogen-rich envelope mass of a dying massive star is the key factor that determines the type and properties of the resulting supernova. Emulating wind-driven mass loss of single stars with the MESA(Modules for Experiments in Stellar Astrophysics) stellar evolution code, we made a grid of models for a large parameter space of initial mass (12 M⊙ to 30M⊙), metallicity (solar, LMC and SMC), hydrogen envelope mass (0.01M⊙ to 10M⊙) for progenitor stars in their final step of evolution. Our results suggest the final luminosity of the progenitor is largely determined by the initial mass, which means there is luminosity degeneracy for stars with the same initial mass but with different hydrogen-rich envelope masses. Since we can break this degeneracy by correcting luminosity with surface gravity (spectroscopic HR diagram), we can infer the exact mass property of an observed progenitor. The surface temperature drastically varies near the envelope mass of ~0.1M⊙ and surface temperature of ~10000 K, where the demarcation between the hydrogen-rich envelope and the helium core lies, which explains the rarity of 'white' supergiants. There also exists a discontinuity in the chemical composition of the progenitor envelope around this critical hydrogen-rich envelope mass of ~0.1 M⊙, which can be tested in future observations of "flash spectroscopy" of supernovae.

• Korean Journal of Materials Research
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• v.30 no.12
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• pp.709-714
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• 2020

For zinc-air batteries, there are several limitations associated with zinc anodes. The self-discharge behavior of zinc-air batteries is a critical issue that is induced by corrosion reaction and hydrogen evolution reaction (HER) of zinc anodes. Aluminum and indium are effective additives for controlling the hydrogen evolution reaction as well as the corrosion reaction. To enhance the electrochemical performances of zinc-air batteries, mechanically alloyed Zn-Al and Zn-In materials with different compositions are successfully fabricated at 500rpm and 5h milling time. Investigated materials are characterized by X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM), and energy dispersive spectrometer (EDS). Alloys are investigated for the application as novel anodes in zinc-air batteries. Especially, the material with 3 wt% of indium (ZI3) delivers 445.37 mAh/g and 408.52 mAh/g of specific discharge capacity with 1 h and 6 h storage, respectively. Also, it shows 91.72 % capacity retention and has the lowest value of corrosion current density among attempted materials.