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Hydrogen is an alternative fuel that is currently being used in fuel cell (FC) applications. This study focuses on electric-assisted bicycles (electric bicycles) powered by FCs and aims to determine the configuration of an FC system based on power demand. Metal hydrides (MHs) were used in the investigation to facilitate the containment of FC systems with improved hydrogen storage capacity. The flow performance was evaluated in our previous study; thus, here we focused on understanding the hydrogen flow characteristics from storage and the weight gain of the cartridge. Through experiments performed on existing electric-assisted bicycles, the relationship between the load weight and the power demand was evaluated. Furthermore, the power capacity of Li-ion batteries and FC systems was compared. No loss in performance was observed up to an additional payload weight of 8 kg. Combining the FC unit with an auxiliary battery offers up to 6.81× benefits with a significant weight capacity (8 kg). It is inferred that the current MH tank design does not support the required amount of hydrogen. The hydrogen flow could be supported by the exhaust heat of the FC to the MH.

Metal hydrides (MHs) can store hydrogen produced from biomass at low pressure and high volumetric energy density. However, the endothermic reaction that occurs during hydrogen discharge decreases the hydrogen flow rate, which prevents the generation of sufficient power for fuel cell (FC) devices. Because a previous study reported that the hydrogen capacity of MHs would drop by approximately 20% due to the hydrogen sulfide contained in hydrogen from biomass, the utilizable amount of hydrogen in MHs should be enhanced. In this study, MH utilization for an FC-assisted bicycle in consideration of waste heat recovery from MH to FC was investigated. The results show that the MH-based hydrogen storage system can weigh 8 kg or lower for the FC bicycle to travel twice the distance of a lithium-ion-battery-derived bicycle. Using the mathematical model of hydrogen discharge from the MH, the heat transfer of a small MH cartridge for the FC bicycle was investigated. The center of the cartridge cooled by approximately 20 K from the initial temperature, indicating the necessity of heat injection into the MH cartridge even if the initial and boundary temperatures were high. It was also concluded that 83% of the hydrogen charged in the MH could be utilized to maintain the hydrogen flow rate to run a 220 W FC.

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