• Transactions of the Korean hydrogen and new energy society
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• v.18 no.3
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• pp.284-291
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• 2007

The Ni-MH batteries for HEV and industry are normally placed in outdoor, consequently causing an too weak discharge power problem due to a cold weather specially in winter time. In order to improve the low temperature performances of the Ni-MH battery for HEV and industrial uses, it has been investigated the low temperature discharge characteristics of Ni-MH battery with various electrolytes at $-18^{\circ}C$. The summary of experimental results are as follows. The low temperature characteristics depended strongly on the characteristics of electrolytes. When the concentration of the electrolytes were too high or too low the low temperature performance was poor. The best electrolyte was composed of KOH 6.2M+LiOH 1.2M. An addition of RbOH or CsOH to electrolyte improved the low temperature performance. The best total concentration of electrolyte composed of KOH, NaOH and LiOH was about 7M.

• Transactions of the Korean hydrogen and new energy society
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• v.28 no.1
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• pp.9-16
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• 2017

Hydrogen forms metal hydrides with some metals and alloys leading to solid-state storage under moderate temperature and pressure that gives them the safety advantage over the gas and liquid storage methods. However, it has disadvantages of slow hydrogen adsorption-desorption time and low thermal conductivity. To improve characteristics of metal hydrides, it is important that activation and thermal conductivity of metal hydrides are improved. In this study, we have been investigated hydrogen storage properties of Hydralloy C among Ti-Mn alloys. Also, the characteristics of activation and thermal conductivity of Hydralloy C were enhanced to improve kinetics of hydrogen adsorption-desorption. As physical activation method, PHEM (planetary high energy mill) was performed in Ar or $H_2$ atmosphere. Hydralloy C was also activated by $TiCl_3$ catalyst. To improve thermal conductivity, various types of ENG (expanded natural graphite) were used. The prepared samples were compacted at pressure of 500 bar. As a result, the activation properties of $H_2$ PHEM treated Hydralloy C was better than the other activation methods. Also, the amounts of hydrogen storage showed up to 1.6 wt%. When flake type ENG was added to Hydralloy C, thermal conductivity and hydrogen storage properties were improved.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.551-555
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• 2005

This paper presents the temperature-pressure characteristics of SMH actuator using a peltier module. The simple SMH actuator, consisting of the plated hydrogen-absorbing alloy as a power source, Peltier elements as a heat source and a cylinder with metal bellows a functioning part has been developed. The SMH actuator is characterized by its small size, low weight, noiseless operation and a compliance similar to that of the human body. A new special metal hydride(SMH) actuator that uses the reversible reaction between the heat energy and mechanical energy of a hydrogen absorbing ally. It is well known that hydrogen-absorbing alloys can reversibly absorb and desorb a large amount of hydrogen, more than about 1000 times as their own volume. To improve the thermal conductivity of the hydrogen-absorbing alloy, an electro-less copper plating has been carried out. The effects of the electro-less copper plating and the dynamic characteristics of the SMH actuator have been studied. The hydrogen equilibrium pressure increases and hydrogen is desorbed by heating the hydrogen-absorbing alloys, whereas by cooling the alloys, the hydrogen equilibrium pressure decreases and hydrogen is absorbed. Therefor, the SMH actuator has the characteristic of being light and easy to use and so is suitable for use in medical and rehabilitation applications.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.145-145
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• 2010

In this paper, we report that the effects of hydrogen doping on the electrical and optical properties of typical transparent conducting oxide films such as ZnO and $SnO_2$ prepared by magnetron sputtering. Recently, density functional theory (DFT) calculations have shown strong evidence that hydrogen acts as a source of n-type conductivity in ZnO. In this work, the beneficial effect of hydrogen incorporation on Ga-doped ZnO thin films was demonstrated. It was found that hydrogen doping results a noticeable improvement of the conductivity mainly due to the increases in carrier concentration. Extent of the improvement was found to be quite dependent on the deposition temperature. A low resistivity of $4.0{\times}10^{-4}\;{\Omega}{\cdot}cm$ was obtained for the film grown at $160^{\circ}C$ with $H_2$ 10% in sputtering gas. However, the beneficial effect of hydrogen doping was not observed for the films deposited at $270^{\circ}C$. Variations of the electrical transport properties upon vacuum annealing showed that the difference is attributed to the thermal stability of interstitial hydrogen atoms in the films. Theoretical calculations also suggested that hydrogen forms a shallow-donor state in $SnO_2$, even though no experimental determination has yet been performed. We prepared undoped $SnO_2$ thin films by RF magnetron sputtering under various hydrogen contents in sputtering ambient and then exposed them to H-plasma. Our results clearly showed that the hydrogen incorporation in $SnO_2$ leads to the increase in carrier concentration. Our experimental observation supports the fact that hydrogen acting as a shallow donor seems to be a general feature of the TCOs.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.4_2
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• pp.705-713
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• 2023

The phenomenon of abnormal climate conditions resulting from greenhouse gas-induced global warming is increasingly prevalent. To address this challenge, global initiatives are underway to adopt environmentally friendly, zero-emission fuels. In this study, we investigate the hydrogen embrittlement characteristics of materials used for eco-friendly hydrogen storage systems. The effects of hydrogen embrittlement on austenitic stainless steels of the FCC series and structural steel of the BCC series were examined. Initially, test samples of three different steel types were prepared in 2t and 3t sizes, and hydrogen was injected into the specimens using an electrochemical method over a 24-hour period. Subsequently, a universal material testing machine (UTM) was employed to monitor changes in mechanical strength and elongation. The FCC series stainless steels exhibited a tendency for elongation to decrease, indicating low sensitivity to hydrogen. In contrast, the mechanical strength and elongation of the BCC series steel changed significantly upon hydrogen charging, posing challenges for prediction. The results of the present study are expected to serve as a fundamental database for analyzing the impact of hydrogen embrittlement on both FCC and BCC series steel materials.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.6
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• pp.555-561
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• 2023

In this study, we proposed a standard model for the design, construction and demonstration of the technology development and substantiation of small hydrogen powered vessel in order to respond to the alternative fuel-using vessel market that requires the use of low-carbon/carbon-free fuel as a greenhouse gas reduction measure. The hydrogen fuel cell-based electric propulsion system developed through this is optimized through performance and durability tests on the land-based test site (LBTS), and the electric propulsion system applied to this result is mounted on a small hydrogen propulsion vessel and operated. Simultaneously, through the digital twin technology between the LBTS and the hydrogen-propelled vessel on the sea, the technology that can predict and diagnose the problems that can occur in the electric propulsion system of the vessel is applied to carry out the empirical study of the hydrogen-propelled vessel. In addition, we propose a commercialization model by analyzing the economic feasibility of the demonstration vessel.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.1
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• pp.1-9
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• 2013

Long term hydrogen production was investigated in an anaerobic sequencing batch reactor (ASBR) using mixed microflora. Glucose (about 8,250 mg/L) was used as a substrate for the ASBR operation under the condition of pH 5.5 and $37^{\circ}C$ with mixing at 150 rpm. The experiment was carried out over a period of 160 days. Hydrogen yield was 0.8mol $H_2/mol$ glucose with F/M ratio 2 at initial operation period. The hydrogen yield reached to maximum 2.6 mol $H_2/mol$ glucose at 80th day operation. However decreased hydrogen yield was observed after 80 days operation and eventually no hydrogen yield. Although well-known hydrogen producer Clostridium sp. was detected in the reactor by PCR-DGGE analysis, changed reactor operation was the major reason of the decreased hydrogen production, such as low F/M ratio of 0.5 and high propionic acid concentration 2,130 mg/L. Consequently the long period operation resulted in MLSS accumulation and then low F/M ration stimulating propionic acid formation which consumes hydrogen produced in the reactor.

• Clean Technology
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• v.29 no.3
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• pp.217-226
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• 2023

The amount of hydrogen adsorbed in arrays of single walled carbon nanotubes (SWNTs) was studied as a function of nanotube diameter and distance between the nearest-neighbor nanotubes on square arrangements using a grand canonical Monte Carlo simulation. The influence of the geometry of a triangle array with the same diameters and distances was also studied. Hydrogen-carbon and hydrogen-hydrogen interactions were modeled with Lennard-Jones potentials for short range interactions and electrostatic interactions were added for hydrogen-hydrogen pairs to consider quantum contributions at low temperatures. At 194.5 K, Type I isotherms for large-diameter SWNTs and Type IV isotherms without hysteresis between adsorption and desorption processes for wider tube separations were observed. At 200 bars, the gravimetric hydrogen storage capacity of the SWNTs was reached or exceeded the US Department of Energy (DOE) target, but the volumetric capacity was about 70% of the DOE target. At 77 K, a two-step adsorption was observed, corresponding to a monolayer formation step followed by a condensation step. Hydrogen was adsorbed first to the inner surface of the nanotubes, then to the outer surface, intratubular space and the interstitial channels between the nanotube bundles. The simulation indicated that SWNTs of various diameters and distances in a wide range of configurations exceeded the DOE gravimetric and volumetric targets at under 1 bar.

• Journal of Korean Society on Water Environment
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• v.28 no.5
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• pp.704-716
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• 2012

This paper provides a detailed account of pilot testing conducted at South Lake Tahoe (California), the Ddukdo (Seoul) water treatment plant (WTP) and the Bokjung (Seongnam) WTP between February, 2010, and February, 2012. The objectives were first, to characterize the reactions of ozone with hydrogen peroxide (Peroxone) for Han River water following sand filtration, second to determine empirical ozone and hydrogen peroxide doses to remove a taste-and-odor surrogate 2-methylisoborneol (MIB) using an advanced oxidation process (AOP) configuration and third, to determine the optimum dosing configuration to reduce residual ozone to a safe level at the exit of the process. The testing was performed in a real-time plant environment at both low- and high seasonal water temperatures. Experimental results including ozone decomposition rates were dependent on temperature and pH, consistent with data reported by other researchers. MIB in post-sand-filtration water was spiked to 40-50 ng/L, and in all cases, it was reduced to below the specified target level (7 ng/liter) and typically non-detect (ND). It was demonstrated that Peroxone could achieve both MIB removal and low effluent ozone residual at ozone+hydrogen peroxide doses less than those for ozone alone. An empirical predictive model, suitable for use by design engineers and operating personnel and for incorporation in plant control systems was developed. Due to a significant reduction in the ozone reaction/decomposition at low winter temperatures, results demonstrate the hydrogen peroxide can be "pre-conditioned" in order to increase initial reaction rates and achieve lower ozone residuals. Results also indicate the method, location and composition of hydrogen peroxide injection is critical to successful implementation of Peroxone without using excessive chemicals or degrading performance.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.1
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• pp.14-21
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• 2008

Synthetic gas is defined as reformed gas from hydrocarbon-based fuel and the major chemical species of the synthetic gas are $H_2$, CO and $N_2$. Among them, hydrogen from synthetic gas is very useful species in chemical process such as combustion. It is a main reason that many studies have been performed to develop an effective reforming device. Furthermore, other technologies have been studied for synthetic gas application, such as the ESGI(Exhaust Synthetic Gas Injection) technology. ESGI injects and burns synthetic gas in the exhaust pipe so that heat from hydrogen combustion helps fast warmup of the close-coupled catalyst and reduction of harmful emissions. However, it is very hard to understand combustion characteristic of hydrogen under low oxygen environment and complicated variation in chemical species in exhaust gas. This study focuses on the characteristics of hydrogen combustion under ESGI operating conditions using a CVC(Constant Volume Chamber). Measurements of pressure variation and flame speed have been performed for various oxygen and hydrogen concentrations. Results have been analyzed to understand ignition and combustion characteristics of hydrogen under lower oxygen conditions. The CVC experiments showed that under lower oxygen concentration, amount of active chemicals in the combustion chamber was a crucial factor to influence hydrogen combustion as well as hydrogen/oxygen ratio. It is also found that increase in volume fraction of oxygen is effective for the fast and stable burning of hydrogen by virtue of increase in flame speed.