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

63 Spectronik PEM fuel cells | Dossier Cell materials and structure As a result of the humidity stability in the Protium cells, each cell generates around 0.8-1 A/cm 2 , compared with 0.6- 0.7 A/cm 2 for equivalent open-cathode systems, according to Spectronik’s tests. This higher current density effectively translates into a higher power-to-cost ratio, as the MEA is often the most expensive part of the fuel cell system. “The membrane is an expanded polytetrafluoroethylene-reinforced ionomer, and is about 15 microns thick,” Jap adds, noting that the company cannot disclose the type and amount of catalyst material used for the electrochemical reaction. The structural layers making up each cell in the Protium stack contain a few innovations. First, the anode separator plate is made from a 0.29 mm flexible graphite foil, which features no flow field for directing the hydrogen; instead, the flow field is stamped directly onto the anode gas diffusion layer (GDL). Spectronik has opted for a graphite foil and anode GDL flow-field configuration, as it is lighter than CNC-machined graphite plate and therefore more suitable for aerospace applications. It is also sufficiently corrosion-resistant compared with metallic plates. “Graphite is very stable chemically, so unlike some metal plates it doesn’t need electroplating or any other coatings,” Jap adds. “It’s also very cost-effective, which helps us to be flexible with our design, as r&d might find better flow- field arrangements for using hydrogen in different integrations and environments. “Also, CNC-machining the hydrogen flow field onto a graphite plate takes more than 100 times longer than stamping it. Stamping is less costly than CNC as well, and we can switch to automated stamping if we get a bulk order. “Additionally, while stamped metal could actually be a lighter and thinner alternative, its chemical stability would be worse than graphite’s.” The GDLs themselves are provided by SGL Carbon Sigracet, although the exact products are undisclosed. The cathode separator plate meanwhile is currently made from CNC-machined graphite plate, to accommodate the necessary height of the oxidant channels’ cross-sectional areas (they are much higher than those of the anodes). For volume production, Spectronik plans Unmanned Systems Technology | June/July 2021 Spectronik was founded in 2011 by CEO Jogjaman Jap and COO Maung Maung Zarli, who had already been working on commercial fuel cell technology for a few years. “While there’s a lot of discussion these days about the green benefits of hydrogen mobility, the reason we started Spectronik was because we saw a specific niche for hydrogen power in aerospace, particularly in UAVs,” Jap says. “Our first customer was Boeing, who saw great maturity in many UAV components such as carbon fibre, propellers, cameras and flight control software, but the problem was achieving longer endurances in small packages.” Boeing’s UAV engineers had been trialling small gasoline engines at the time, which they judged as problematic in terms of reliability, MTBFs, vibration, heat signatures and emissions. Switching to all-electric powertrains would remove many of these issues, but lithium batteries had proven too heavy and not worth the minimal amount of flight time they gave. In 2014 therefore, Boeing invited Spectronik to develop hydrogen fuel cells for its Type 2 (up to 25 kg MTOW) fixed- wing UAV test platform, so over the following two years Spectronik produced an open-cathode, air-cooled fuel cell to Boeing’s specifications in form factor and temperature. Towards the completion of the research project, in 2016, Boeing gave Spectronik’s 250 W cell its highest ratings on size, weight, performance, energy storage, firmware stability and quality of workmanship. Around the same time, Jap and Zarli felt that considerable improvements in performance, precision and reliability could be achieved by developing a closed-cathode architecture, so they formulated and produced one over the following two years. By 2018, Spectronik had supplied both open- and closed- cathode cells to a number of UAV manufacturers (both fixed- wing and multi-rotor) in defence and commercial markets across Southeast Asia and Australia. Most recently this has included a UAV from Thunder Tiger Robotix called the H2-X6 Phoenix. This is a carbon fibre hexacopter that can fly for up to 90 minutes while carrying a 2 kg payload (or 120 minutes with no payload), as well as a 9 litre tank for hydrogen stored at 40 MPa working pressure. That powers a Protium-2000 cell, equipped with a 5000 mAh 9S lithium-polymer hybrid battery for high transients. Overall, the H2-X6 Phoenix has a 21 kg MTOW and is designed principally for infrastructure inspections and similar commercial applications, with its hydrogen powertrain enabling a 30 km flight range as well as a wi-fi comms range of 2 km (over 2.4 GHz) and a 20 km, 433 MHz link. “Projects such as these have given us valuable experience in the precision engineering of fuel cells and how to integrate them on different shapes and sizes of UAS, in terms of packaging, centre of gravity, power distribution and comms,” Jap adds. Company history