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77 Teledyne Energy Systems EDR fuel cell | Dossier critical for achieving a viable MTBF with the EDR cell’s internal environment. Dr Valdez notes that metal BPPs can be produced via automated stamping to manufacture them in vast quantities at low cost, and that Teledyne would probably start looking to switch from carbon composite plates to stamped metal ones if a customer wanted their cells in quantities befitting that. “Manufacturers such as Toyota and Intelligent Energy have made huge advances in automated metal BPP production, which works great for fuel cells that use the ambient air as their oxygen source,” he says. “And their usual problem of gases corroding the metals is starting to become less of a problem as well, now that companies like Treadstone are developing really effective coatings for corrosion resistance in stainless steel BPPs, so it’s something we’re keeping a close eye on. “Companies taking the mass- production route on fuel cells also save huge amounts of money using larger, encircling, single-piece gaskets that are fabricated separately and then attached around the whole MEA. But we can’t risk any leakage in the applications we’re designing towards, so each seal is individually deposited and formed. “That individual configurability is another reason why we’re not yet auto-stamping metal BPPs for our cell. Carbon plates are certainly expensive to make – they account for 30-50% of our production costs, compared with 15- 21% for metal BPP users – but stamping metal plates means giving up the ability to make really fine changes to how the electrodes and gas channels are designed from one stack to the next.” Water management As the exhaust products exit the cell stack, they first pass through an orifice leading into the water management unit. Water in the exhaust separates from the gas stream on the upper (of two) layers or ‘floors’ inside this section. Although the oxygen from the exhaust continues to be drawn by the Venturi effect towards the BoP manifold through an exit port, the now-liquid water is largely too heavy to be vacuumed in this way. To ensure all the water is evacuated, the floors are made from a hydrophilic material called Supore (sometimes called Nupore), which was chosen for its high water permeability. The Supore pulls water from the top to the bottom of the unit, where an exit pipe is fixed for the water to flow out to the exhaust pump. This will be disposed of or distributed in the way most fitting for the vehicle in question, such as a UUV ballast distribution system. “The original idea used both hydrophobic and hydrophilic layers in the water management, to have a combined push and pull of water through the unit,” Dr Valdez says. “But since our carbon BPPs are inherently hydrophobic, they passively repel the water vapour, causing it to separate and shoot out of the stack area, into the exit channel and down into the water unit’s hydrophilic layers. “That’s another problem with metal plates – metal is inherently somewhat hydrophilic, so they need either a coating or treatment to make them repel water or made even more hydrophilic so the water can be wicked away.” Valdez adds that Teledyne has received $2.8 million from NASA to test how well the water management system works in microgravity conditions, particularly if the hydrophilic material – which in the space version could have multiple ‘tentacles’ that would increase its collision area – is sufficient for collecting all the water droplets bouncing around in space. The future Teledyne plans to continue producing small numbers of high-efficiency fuel cells, but it will also invest in larger-scale designs and equipment, using automated production, if the right customer or a surge in the space economy should warrant it. Unmanned Systems Technology | December/January 2021 The water management unit uses layers of hydrophilic material to draw away water, while reactants continue flowing towards the balance of plant