Korea, Republic of

Due to the low density of hydrogen gas under ambient temperature and atmospheric pressure conditions the high-pressure gaseous hydrogen storage method is widely employed. With high-pressure characteristics of hydrogen storage rigorous safety precautions are required such as filling of compressed gas in a hydrogen tank to achieve reliable operational solutions. Especially for the large-sized tanks (above 150 L) safety operation of hydrogen storage should be considered. In the present study the compressed hydrogen gas behavior in a large hydrogen tank of 175 L is investigated for its filling. To validate the numerical approach used in this study numerical models for the adaptation of the gas and turbulence models are examined. Numerical parametric studies on hydrogen filling for the large hydrogen tank of 175 L are conducted to estimate the hydrogen gas behavior in the hydrogen tank under various conditions of state of charge of pressure and ambient temperature. From the parametric studies the relationship between the initial SOC pressure condition and the maximum temperature rise of hydrogen gas was shown. That is the maximum temperature rise increases as the ambient temperature decreases and the rise increases as the SOC decreases.

With the rapid growth in demand for effective and renewable energy the hydrogen era has begun. To meet commercial requirements efficient hydrogen storage techniques are required. So far four techniques have been suggested for hydrogen storage: compressed storage hydrogen liquefaction chemical absorption and physical adsorption. Currently high-pressure compressed tanks are used in the industry; however certain limitations such as high costs safety concerns undesirable amounts of occupied space and low storage capacities are still challenges. Physical hydrogen adsorption is one of the most promising techniques; it uses porous adsorbents which have material benefits such as low costs high storage densities and fast charging–discharging kinetics. During adsorption on material surfaces hydrogen molecules weakly adsorb at the surface of adsorbents via long-range dispersion forces. The largest challenge in the hydrogen era is the development of progressive materials for efficient hydrogen storage. In designing efficient adsorbents understanding interfacial interactions between hydrogen molecules and porous material surfaces is important. In this review we briefly summarize a hydrogen storage technique based on US DOE classifications and examine hydrogen storage targets for feasible commercialization. We also address recent trends in the development of hydrogen storage materials. Lastly we propose spillover mechanisms for efficient hydrogen storage using solid-state adsorbents.

Microbial electrolysis cells (MECs) have attracted significant interest as sustainable green hydrogen production devices because they utilize the environmentally friendly biocatalytic oxidation of organic wastes and electrochemical proton reduction with the support of relatively lower external power compared to that used by water electrolysis. However the commercialization of MEC technology has stagnated owing to several critical technological challenges. Recently many attempts have been made to utilize nanomaterials in MECs owing to the unique physicochemical properties of nanomaterials originating from their extremely small size (at least <100 nm in one dimension). The extraordinary properties of nanomaterials have provided great clues to overcome the technological hurdles in MECs. Nanomaterials are believed to play a crucial role in the commercialization of MECs. Thus understanding the technological challenges of MECs the characteristics of nanomaterials and the employment of nanomaterials in MECs could be helpful in realizing commercial MEC technologies. Herein the critical challenges that need to be addressed for MECs are highlighted and then previous studies that used nanomaterials to overcome the technological difficulties of MECs are reviewed.

Formaldehyde (H2CO) is the harmful chemical that used in variety of industries. However there are many difficulties to treat discharged H2CO in the wastewater. Hydrogen energy is arising as a one of the renewable energy that can replace fossil fuel. Many researches have been conducted on hydrogen production from electrolysis using expensive metal electrodes and catalysts such as platinum (Pt) and palladium (Pd). However they are expensive and have obstacles to directly use from the production. We used copper (Cu) as an electrode substrate because it has a good current density. To avoid corrosion issue of Cu substrate we used commercially available carbon (C) coated Cu substrate and synthesized titanium (Ti) on C/Cu substrate. We found that Ti was well synthesized and stayed on substrate after hydrogen evolution reaction (HER) in artificial wastewater. Moreover we quantified hydrogen production from the wastewater and compared it to pure water. Hydrogen production was enhanced in wastewater and H2CO was decomposed after reaction. We expected to use Ti-C/Cu electrode for hydrogen production of wastewater by electrolysis.

During the fast-filling of a high-pressure hydrogen tank the temperature of hydrogen would rise significantly and may lead to failure of the tank. In addition the temperature rise also reduces hydrogen density in the tank which causes mass decrement into the tank. Therefore it is of practical significance to study the temperature rise and the amount of charging of hydrogen for hydrogen safety. In this paper the change of hydrogen temperature in the tank according to the pressure rise during the process of charging the high-pressure tank in the process of a 82-MPa hydrogen filling system the final temperature the amount of filling of hydrogen gas and the change of pressure of hydrogen through the pressure reducing valve and the performance of heat exchanger for cooling high-temperature hydrogen were analyzed by theoretical and numerical methods. When high-pressure filling began in the initial vacuum state the condition was called the “First cycle”. When the high-pressure charging process began in the remaining condition the process was called the “Second cycle”. As a result of the theoretical analysis the final temperatures of hydrogen gas were calculated to be 436.09 K for the first cycle of the high-pressure tank and 403.55 for the second cycle analysis. The internal temperature of the buffer tank increased by 345.69 K and 32.54 K in the first cycle and second cycles after high-pressure filling. In addition the final masses were calculated to be 11.58 kg and 12.26 kg for the first cycle and second cycle of the high-pressure tank respectively. The works of the paper can provide suggestions for the temperature rise of 82 MPa compressed hydrogen storage system and offer necessary theory and numerical methods for guiding safe operation and construction of a hydrogen filling system.

This study established global warming potential(GWP) emission factors through a life cycle assessment on the operation phases of two different 1 kW polymer electrolyte membrane fuel cell (PEMFC) systems for residential buildings (NG-PEMFC fed with hydrogen from natural gas reforming; WE-PEMFC fed with hydrogen from photovoltaics-powered water electrolyzer). Their effectiveness was also compared with conventional power grid systems in Korea specifically in the area of greenhouse gas emissions. The operation phases of the NG-PEMFC and the WE-PEMFC were divided into burner reformer and stack and into water electrolysis and stack respectively. The functional unit of each fuel cell system was defined as 1 kWh of electricity production. In the case of NG-PEMFC the GWP was 3.72E-01 kg-CO2eq/kWh the embodied carbon emissions due to using city gas during the life cycle process was about 20.87 % the carbon emission ratio according to the reformer's combustion burner was 6.07 % and the direct carbon emission ratio of the air emissions from the reformer was 73.06 % indicating that the carbon emission from the reformer contributed over 80 % of the total GWP. As for the WE-PEMFC the GWP was 1.76E-01 kg-CO2eq/kWh and the embodied carbon emissions from photovoltaic power generation during the life cycle process contributed over 99 % of the total GWP.

As the demand for alternative fuels to solve environmental problems increases worldwide due to the greenhouse gas problem this study predicted the demand for liquid hydrogen fuel in aviation to achieve ‘zero‐emission flight’. The liquid hydrogen fuel models of an aircraft and all aviation sectors were produced based on the prediction of aviation fleet growth through the classification of currently operated aircraft. Using these models the required amount of liquid hydrogen fuel and the total cost of liquid hydrogen were also calculated when various environmental regulations were satisfied. As a result it was found to be necessary to convert approximately 66% to 100% of all aircraft from existing aircraft to liquid hydrogen aircraft in 2050 according to regulations. The annual liquid hydrogen cost was 4.7–5.2 times higher in the beginning due to the high production cost but after 2030 it will be maintained at almost the same price and it was found that the cost was rather low compared to jet fuel.

Hydrogen which has a high energy density and does not emit pollutants is considered an alternative energy source to replace fossil fuels. Herein we report an experimental study on hydrogen leaks and ventilation methods for preventing damage caused by leaks from hydrogen fuel cell rooms in homes among various uses of hydrogen. This experiment was conducted in a temporary space with a volume of 11.484 m3 . The supplied pressure leak-hole size and leakage amount were adjusted as the experimental conditions. The resulting hydrogen concentrations which changed according to the operation of the ventilation openings ventilation fan and supplied shutoff valve were measured. The experimental results showed that the reductions in the hydrogen concentration due to the shutoff valve were the most significant. The maximum hydrogen concentration could be reduced by 80% or more if it is 100 times that of the leakage volume or higher. The shutoff valve ventilation fan and ventilation openings were required to reduce the concentrations of the fuel cell room hydrogen in a spatially uniform manner. Although the hydrogen concentration in a small hydrogen fuel cell room for home use can rapidly increase a rapid reduction in the concentration of hydrogen with an appropriate ventilation system has been experimentally proven.

The hydrogen storage pressure in fuel cell vehicles has been increased from 35 MPa to 70 MPa in order to accommodate longer driving range. On the downside such pressure increase results in significant temperature rise inside the hydrogen tank during fast filling at a fueling station which may pose safety issues. Installation of a chiller often mitigates this concern because it cools the hydrogen gas before its deposition into the tank. To address both the energy efficiency improvement and safety concerns this paper proposed an on-board cold thermal energy storage (CTES) system cooled by expanded hydrogen. During the driving cycle the proposed system uses an expander instead of a pressure regulator to generate additional power and cold hydrogen gas. Moreover CTES is equipped with phase change materials (PCM) to recover the cold energy of the expanded hydrogen gas which is later used in the next filling to cool the high-pressure hydrogen gas from the fueling station.

Hydrogen energy has been assessed as a clean and renewable energy source for future energy demand. For harnessing hydrogen energy to its fullest potential storage is a key parameter. It is well known that important hydrogen storage characteristics are operating pressure-temperature of hydrogen hydrogen storage capacity hydrogen absorption-desorption kinetics and heat transfer in the hydride bed. Each application needs specific properties. Every class of hydrogen storage materials has a different set of hydrogenation characteristics. Hence it is required to understand the properties of all hydrogen storage materials. The present review is focused on the state-of– the–art hydrogen storage materials including metal hydrides magnesium-based materials complex hydride systems carbonaceous materials metal organic frameworks perovskites and materials and processes based on artificial intelligence. In each category of materials‘ discovery hydrogen storage mechanism and reaction crystal structure and recent progress have been discussed in detail. Together with the fundamental synthesis process latest techniques of material tailoring like nanostructuring nanoconfinement catalyzing alloying and functionalization have also been discussed. Hydrogen energy research has a promising potential to replace fossil fuels from energy uses especially from automobile sector. In this context efforts initiated worldwide for clean hydrogen production and its use via fuel cell in vehicles is much awaiting steps towards sustainable energy demand.