Unmanned Systems Technology 038 l Skyeton Raybird-3 l Data storage l Sea-Kit X-Class USV l USVs insight l Spectronik PEM fuel cells l Blue White Robotics UVIO l Antennas l AUVSI Xponential Virtual 2021 report

64 Dossier | Spectronik PEM fuel cells to switch to compression moulding, to save time and costs. On the opposite side of each cell assembly from the anode separator plate is a cooling fin made from corrugated 0.05 mm stainless steel. They incorporate an offset fin design, which compared with standard straight fins helps induce greater turbulence in the incoming airflow (meaning an increase in the overall cooling effect), as well as providing higher structural strength to avoid deformations from the cells having to be tightly sealed and pressurised. They are then coated in gold for corrosion resistance and conductivity. “The offset design and ultra-conductive gold plating together achieve very good in-plane electrical conductivity,” Zarli adds. “There’s less need for through- plane electrical conductivity, as the current will flow along the gold plating.” Jap notes, “Like the anode GDL design, the cooling fin design is quite mature. We’re confident that we’ve fully optimised it, which is why we’ve invested in die-sets for stamping them. In a typical open-cathode cell stack, electroplatings such as gold with a nickel underlay can corrode and poison the cell, leading to premature drops in performance and stack failure. “However, as the metallic cooling fin is never in direct contact with the cathode in this fuel cell – only the graphite separator plates – such a situation is avoided. Also, no by-product water is ever in contact with the cooling fin, further reducing the possibility of corrosion. As a result, overall stack lifetime is increased.” Lastly, each cell is sealed using a self-curing adhesive gasket, which is installed using an automated dispensing mechanism. June/July 2021 | Unmanned Systems Technology A breakdown of the layers in each closed-cathode cell, with hydrogen flow indicated in blue, oxidant in red and cooling airflow in green The anode separator plate (upper) is 0.29 mm thick and made of graphite foil, while the anode flow field is stamped directly into the gas diffusion layer (lower) In a typical open- cathode cell stack, electroplating with gold with a nickel underlay can poison and corrode the cell, leading to stack failure