(378ag) High Energy Density Energy Storage System Composed of Electrolyzer, Metal Hydride, and Fuel Cell

Hydrogen is attracting great attention as a promising energy source due to its high energy storage density, environmental friendliness, and connectivity with renewable energy sources. However, there are disadvantages in that the charging hydrogen is restricted due to the lack of infrastructure and hydrogen is difficult to handle without proper equipment. In this study, a novel type of reversible energy storage system that uses water as a reactant without hydrogen supply has been developed. This energy storage system was specialized to enhance volumetric energy storage density compared to conventional Li-ion battery in the portable application area. The core technologies of the system are water electrolyzer, metal hydride, and fuel cell. The charging unit is composed of a pressurized-type water electrolyzer and BOPs (Balance of plant) including a water booster pump and the dryer module. The discharging unit is composed of an AB₅ type metal hydride based hydrogen storage cylinder, an air-breathing type PEMFC (Polymer electrolyte membrane fuel cell) stack which can be operated without humidifying device, and a DC/DC converter. In the charging process, water is converted into hydrogen through electrochemical reaction in the electrolyzer of the charging unit and hydrogen is stored in the metal hydride of the discharging unit. During the discharge process, the stored hydrogen is converted into electricity and water through electrochemical reaction in the PEMFC stack of the discharging unit. In this study, high pressure operation of the electrolyzer, PCT (Pressure-concentration-temperature) characteristics of the AB₅ type metal hydride, and the high efficiency operating conditions of the PEMFC stack were studied. In addition, energy charging and discharging characteristics were experimentally investigated when core components were integrated. From the experimental results, effective design approach for enhancing charging/discharging characteristics of this system were proposed.