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69 forgo mechanical pumps in favour of passive, nozzle-based systems (similar to injectors) for feeding oxygen and hydrogen into the cell. This eliminates a key point of potential failure and parasitic energy consumption, with the pressure difference between the storage tanks and the fuel cell stack effectively providing the energy required to recirculate the reactants through the stack. In the EDR cell, the reactant circulation and management system works on the basis of the Venturi effect, in which gases are forced to speed up when passing through a choke point. A nozzle is installed inside the inlet channel for the oxygen coming from its tank and pressure regulator, which narrows to accelerate the gas. That increase in speed causes the oxygen’s pressure in that section to drop. This area is also where the fuel cell’s fluid output channel – which serves principally to carry water as well as unused reactant out of the stack – connects to the oxygen intake. That low pressure, and the open channel from the exhaust side of the cell stack, effectively vacuums the exhaust out of the stack. Along the way, the water is completely extracted via the water management system, leaving only unused reactant that is then recombined with the incoming reactant. Also, and unlike the hydrogen fuel cells previously featured in this magazine, the EDR cell has been designed to use tanks of pure oxygen rather than draw oxygen from the air. Many other hydrogen systems, such as those from Protonex ( UST 14, June/July 2017), BMPower ( UST 22, October/November 2018) and Intelligent Energy ( UST 24, February/ March 2019) simply draw their oxygen from the ambient air – but of course there is no ambient air in space or underwater. This requirement has defined many of the critical material choices and design parameters for the EDR cell. Although highly customisable (as is typical for PEMFCs), the standard EDR cell is a 15.4 kg system that is 566 mm tall, 180 mm wide and 110 mm on its thinnest side. It produces a maximum continuous power of 6 kW, with a peak of 8 kW at 80 V. It has been configured for a range of actual and proposed uses across many UUVs and spacecraft, including newer generations of heavy XLUUV-type craft designed to operate for months at a time between refuelling, and for diving and performing surveys at depths of more than 3000 m. It forms the power source for Teledyne’s Subsea Supercharger solution, which is currently available as a 100 kWh hydrogen energy storage and supply unit. This basic version is capable of outputting 8 kW for recharging, and is packaged in a 1.5 x 1.5 x 1.4 m frame, with a total weight in air of 800 kg. It can be equipped modularly with Teledyne Energy Systems EDR fuel cell | Dossier The reactant circulation and management system uses the Venturi effect, where gases speed up through a choke point Unmanned Systems Technology | December/January 2021 In addition to being available for UUV, UAV and ground vehicles, EDR fuel cells are being applied in Teledyne’s Subsea Superchargers for replenishing UUV batteries