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    Numerical and experimental studies on unitized regenerative proton exchange membrane fuel cell
    (Pergamon-Elsevier Science Ltd, 2023) Yelegen, Nebi; Kumuk, Berre; Kaplan, Ruveyda N.; Ilbas, Mustafa; Kaplan, Yuksel
    Increasing energy need and running out of fossil-based fuels direct us to renewable energy resources. Although hydrogen is not an energy source by itself, it is an energy carrier with a high specific heat capacity. As it is used as fuel in unitized regenerative PEM fuel cells, water is separated in electrolyzer mode and stored by producing hydrogen when there is no need for energy. In this study, performance tests on the unitized regenerative PEM electrolyzer/fuel cell were carried out and numerical modelling has been performed. The validity of the developed model was confirmed by the results of the experimental study. Before starting the performance tests, the cell's leakproofness tests were carried out, and the appropriate torque force was optimized, reducing the contact resistance that causes performance loss. The material selection of the cell components and corrosion-resistant materials that can operate in both electrolyzer and fuel cell modes were preferred. In this study, 0.019 slpm of hydrogen and 0.0095 slpm of oxygen gas is produced in the electrolyzer mode, while a power density of 0.353 W/cm2 is obtained in the fuel cell mode at 80 degrees C, from a unitized regenerative PEM fuel cell with a 5 cm2 active area, whose cell elements are combined with a 3 Nm clamping torque by using 12 bolts. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    The effect of powder and pellet forms of added metal hydride materials on reaction kinetics and storage
    (Pergamon-Elsevier Science Ltd, 2024) Atalmis, Gamze; Sattarkhanov, Kurshod; Kaplan, Ruveyda N.; Demiralp, Mehmet; Kaplan, Yuksel
    In the present research, metal hydride pellets were synthesized to enhance the kinetics of hydrogen charge/ discharge processes. By incorporating ENG (expanded natural graphite) and copper additives, we observed improvements in the heat transfer coefficients and storage capacities of the hydrogen storage materials. The reactor is designed to contain 1000 g of storage material in the form of powder or 25 pellets each weighing 40 g. The influence of storage materials with enhanced thermal conductivity on the hydrogen charge/discharge process was experimentally studied in a metal hydride reactor under a pressure of 10 bar. The reactor was heated under vacuum (10-4-4 mmHg) to approximately 200 degrees C for 2 h in order to complete the activation process. Following the heating process, the reactor was allowed to cool to ambient temperature, after which the hydrogen was introduced to the reactor at 10 bar pressure for 50 min. The absorption and desorption procedure was reiterated up to 20 cycles, and recordings of data were taken at intervals of 5 cycles to monitor the variations between the cycles. After 10 charge/discharge cycles under pressure of 10 bar, the hydrogen stored in the reactor amounted to approximately 9.93 g in pellet form and 7.20 g in powder form.