6. Hydrogen Fueling Performance Analysis of Metal Hydride for a Fuel-Cell-Assisted Bicycle Using GF-08 Cooling System

Metal hydride (MH) is an alloy that reversibly reacts with hydrogen gas and charges/discharges hydrogen into/from it. MH has some merits, such as low-pressure hydrogen storage, which can contribute to the abatement of environmental impacts, and high volumetric density, which can enhance the operation time per one charge. However, MH requires a long hydrogen charging time owing to the temperature increase caused by the exothermic reaction in its hydrogen-charging process. To address this problem, MH can be cooled to prevent the temperature increase during hydrogen charging. Thus, in this study, an MH cooling system using natural refrigerant GF-08 (MHG system) was investigated and compared with an MH cooling system using R410A (MHR system) and a conventional lithium-ion-battery-based energy storage system (Li-ion battery (LIB) system) in terms of the equivalent CO₂ emission and charging time. It was determined that the CO₂ reduction rate of the MHG system was 14.9% (MHR system) and 9.43% (LIB system). Moreover, by focusing on the charging time, it was found that the charging time of the LIB system was 10.3 times longer than those of the MHG and MHR systems. Therefore, MH cooling using GF-08 was proved to be effective at reducing both equivalent CO₂ emissions and charging time compared to the MH cooling system using R410A and a lithium ion battery.