• Journal of Electrochemical Science and Technology
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• v.13 no.1
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• pp.120-127
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• 2022

Molybdenum disulfide (MoS₂) has been widely used as a catalyst for the bifunctional activities of hydrogen and oxygen evolution reactions (HER and OER). Here, we investigated size dependent HER and OER performance of MoS₂. The smallest size (90 nm) of MoS₂ exhibits the lowest overpotential of -0.28 V at -10 mAcm^-2 and 1.52 V at 300 mAcm^-2 with the smallest Tafel slopes of 151 and 176 mVdec^-1 for HER and OER, respectively, compared to bigger sizes (2 ㎛ and 6 ㎛) of MoS₂. The better HER and OER performance is attributed to high electrochemical active surface area (6 × 10^-4 cm²) with edge sites and low charge transfer resistance (18.1 Ω), confirming that the smaller MoS₂ nanosheets have the better catalytic behavior.

• Korean Journal of Metals and Materials
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• v.48 no.12
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• pp.1123-1129
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• 2010

In order to apply the Sievert's type automatic apparatus to thermal analysis of hydrogen absorbing materials, the dehydrogenation of the Mg-H system was investigated. As the initial wt% of hydrogen was increased to 4.4, the peak temperature of evolution rate shifted to higher temperature. However, with the initial wt% of hydrogen higher than 4.4, peak temperature of evolution rate did not change. The peak temperatures of evolution rate obtained by automatic apparatus were almost the same as those measured by a manual apparatus. As the heating rate was increased, the peak temperatures increased; the peak temperatures for heating rates 1, 2 and 3 K/min were 664, 687 and 702 K, respectively. The activation energy for the decomposition of Mg hydride was 101 kJ/mol. The Sievert's type automatic apparatus can be successively applied to the thermal analysis of metal hydride.

• Bulletin of the Korean Chemical Society
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• v.21 no.8
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• pp.805-808
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• 2000

Mixed crystal powders based on Cd,Fe, and S have been synthesized by varying the ratio of CdS and $FeS_2in$ order to find a suitable material usefuI for the effectivc conversion of solar energy. Hydrogen gas was evolved only with CdS/Ptby photocatal ytic reaction under white light in an aqueous 1 M sodiumsulfite solution. From electrochemical studies of semiconductor electrodes. itwas shown that the onset potential shifted to the positive direction and that the bandgap energy also decreased as the molar ratio of Fe increased. A hydrogen evolution mechanism in terms of the conduction band potential and hydrogen evolution potential is proposed.

• Microbiology and Biotechnology Letters
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• v.11 no.3
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• pp.211-216
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• 1983

Rhodopseudomonas sphaeroides K-7 evolves large quantities of molecular hydrogen under anaerobic and light illuminated conditions in the presence of utilizable organic compounds as electron donors. Photoevolution of molecular hydrogen was strictly dependent on light as the activity of nitrogenase in this organism. Both of these were inhibited to the nearly same extent at varying concentrations of ammonium ion which also depressed nitrogenase synthesis. In the reaction mixtures devoid of molybdenum ion which is known as the component of nitrogenase, hydrogen evolution also decreased similarly like nitrogenase activity. Photoevolution of molecular hydrogen appeared to have no relationship with hydrogenase activity and bacteriocholophyll content and it was markedly inhibited under the atmosphere of $C_2$H$_2$, $N_2$ or $O_2$. The results strongly indicate that hydrogen evolution by R. sphaeroides K-7 might be catalyzed by nitrogenase. Both hydrogen evolution and nitrogenase activity were largely influenced by the nutritional history of the resting cells. From which we propose that glutamate might play an important role in the regulation of nigrogenase activity in vivo.

• Microbiology and Biotechnology Letters
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• v.13 no.3
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• pp.257-263
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• 1985

Rhodopseudomonas sp. KCTC 1437 evolved molecular hydrogen efficiently under light illuminated anaerobic culture condition in the presence of organic acids and various sugars. especially glucose when low concentration of NH$_4$ + or L-glutamate was added to cultures. It was revealed that hydrogen formation from Rhodopseudomonas sp. KCTC 1437 was mediated by two different enzyme systems. Under the nitrogen limiting condition, hydrogen evolution from glucose was catalyzed by nitrogenase. For the nitrogenase activation in vivo, the precultured cells drown on limiting concentration of NH$_4$$^{+}$ as a sole nitrogen source showed more capacity of hydrogen evolution from glucose in the presence of L-glutamate than any other cells .frown on sufficient concentration of NH$_4$$^{+}$, L-glutamate, NH$_4$$^{+}$, or both of L-glutamate and $N_2$. A significant volume of molecular hydrogen was evolved from glucose even in the presence of excess NH$_4$$^{+}$ either in the light or dark anaerobic condition, presumably due to the mediation of hydrogen evolution by fromic hydrogenlyase.enlyase.

• Korean Chemical Engineering Research
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• v.61 no.4
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• pp.627-634
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• 2023

Graphitic carbon nitride (g-C₃N₄) has attracted considerable attention since its discovery for its catalysis of water splitting to hydrogen and oxygen under visible light irradiation. However, pristine g-C₃N₄ confers only low photocatalytic efficiency and requires surface cocatalysts to reach moderate activity due to a lack of accessible surface active sites. Inspired by the high specific surface area and superior electron transfer of graphene, we developed a strongly coupled binary structure of graphene and g-C₃N₄ aerogel with 3D porous skeleton. The as-prepared 3D structure photocatalysts achieve a high surface area that favors efficient photogenerated charge separation and transfer, enhances the light-harvesting efficiency, and significantly improves the photocatalytic hydrogen evolution rate as well. The photocatalyst performance is observed to be optimized at the ratio 3:7 (g-C₃N₄:GO), leading to photocatalytic H₂ evolution of 16125.1 mmol. g^-1. h^-1 under visible light irradiation, more than 161 times higher than the rate achieved by bulk g-C₃N₄.

• The Korean Journal of Food And Nutrition
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• v.10 no.4
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• pp.549-552
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• 1997

A purple non-sulfur photosynthetic bacteria which evolved molecular hydrogen efficiently from glucose in the presence of low concentration of NH4+ under light illuminated anaerobic condition was isolated from mud samples in Korea. This bacteria was identified on Rhodobacter sphaeroides KS 56 based on the morphological, cultural and physiological characteristics.

• Korean Journal of Materials Research
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• v.26 no.5
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• pp.241-245
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• 2016

Hydrogen is considered a potential future energy source. Among other applications of hydrogen, hydrogen-rich water is emerging as a new health care product in industrial areas. Water electrolysis is typically used to generate a hydrogen rich water system. We annealed 10AA carbon paper in air to use it as an electrode of a hydrogen rich water generator. Driven by annealing, structural changes of the carbon paper were identified by secondary electron microscope analysis. Depending on the various annealing temperatures, changes of the hydrophilic characteristics were demonstrated. The crystal structures of pristine and heat-treated carbon paper were characterized by X-ray diffraction. Improvement of the efficiency of the electrochemical oxygen evolution reaction was measured via linear voltammetry. The optimized annealing temperature of 10AA carbon paper showed the possibility of using this material as an effective hydrogen rich water generator.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.1
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• pp.25-31
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• 2018

To apply Sievert's type apparatus to thermal analysis of hydrogen absorption materials, the dehydrogenation of $LaNi_5$ system was investigated. As the initial wt% of hydrogen was increased from 0.44 to 1.24 wt%, the peak temperature of evolution rate shifted to higher temperature. However, with the initial wt% of hydrogen higher than 0.95 wt%, the peak temperature of evolution rate did not change. As the heating rate was increased, the peak temperature increased; the peak temperatures for heating rates 0.5, 1.0 and 1.5 K/min were 262.2, 264.1, and 265.9 K respectively. The Sievert's type automatic apparatus can be successively applied to the thermal analysis of $LaNi_5$ hydride.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.70.1-70.1
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• 2020

A type IIb supernova (SN IIb) is the result of core-collapse of a massive star which lost most of its hydrogen-rich envelope during its evolution. The pre-SN progenitor properties, such as the total radius and the mass of the hydrogen-rich envelope, can widely vary due to the mass-loss history of the progenitors. Optical light curves of SNe IIb are dominated by energy released by the hydrogen recombination and the radioactive decay of 56Ni in the early and late epochs respectively. This may result in distinctive double peaked light curves like the one observed in SN 1993J. The first peak, caused by the hydrogen recombination, can be modelled with numerical simulations providing information on the pre-SN progenitor properties. We compare two radiation-hydrodynamics codes, STELLA and SNEC, that are frequently used in SNe modelling, and investigate the effect of opacity treatment on the temporal evolution of the color temperature of SNe and eventually on the optical light curves. We find that with a proper treatment of the scattering opacity, SNe IIb models exploded from the progenitor models evolved with latest stellar evolution model hardly match the observational data. We also discuss the smaller scale features found in the models during hydrogen recombination phase.