Uncrewed Systems Technology 047 l Aergility ATLIS l AI focus l Clevon 1 UGV l Geospatial insight l Intergeo 2022 report l AUSA 2022 report I Infinity fuel cell l BeeX A.IKANBILIS l Propellers focus I Phoenix Wings Orca

85 Infinity APWR fuel cell | Dossier exhibit high resistance at the points of interface. Furthermore, the process is time- consuming and difficult to control. Metal BPPs can also (as per Toyota’s approach) be mass-produced using stamping machinery, an approach that achieves very fine control and quality of parts, but the set-up costs of such a facility are really high. CNC-machining such plates is similarly costly to set up, and the integrity of the resulting BPPs can vary owing to how the metals are cut. To overcome these various drawbacks and cost barriers, Infinity’s approach is to use a patented approach involving diffusion bonding. This is essentially a welding process in which multiple layers of metallic ‘foils’ are pressed together (most often in a vacuum chamber) at a specific pressure as well as a temperature of usually around 50-90% of the most fusible material’s melting point, with increases in the temperature aiding in the interdiffusion of the different atoms across the face of the joint. The boundaries between the metal layers therefore disappear during the bonding process, ensuring high electrical conductivity and pressure integrity, as well as lower weight and greater ruggedness. This contributes to the survivability and power-to-weight ratio desired by most of Infinity’s naval, aerial and space users. Diffusion bonding appeals to Infinity for other reasons. For instance, given that the process largely revolves around controlling the pressure, temperature and holding time across the areas of the materials being bonded, it can be largely automated. While current volumes are low, high-volume automated production might be possible to scale up manufacturing in the future. “We also get a high degree of control over the design of each flow field, so we can get hydrogen and oxygen to exactly where we want them, for proper stoichiometry and efficiency across the active area of each MEA,” Smith says. And for any Infinity PEMFCs using metallic porous membranes for the APWR process, the membrane can be directly diffusion bonded into the BPP assembly, further simplifying the production process. Alternatively, if polymer-based membranes are chosen (to reduce weight), the membrane must be incorporated into the cell separately. “It’s difficult to overstate how robust and rugged the plates resulting from diffusion bonding are,” Smith notes. “And I think the industry is finding stainless steel plates becoming more common, even in fuel cells using ambient air, because it’s a much less expensive and more effective material than alternatives for BPPs.” He adds that the BPPs also have a protective coating layer, which as well as enhancing their ruggedness adds conductivity, minimising the interfacial contact resistance and hence current losses throughout the stack – mitigating a common issue with PEMFCs. “Also, the way we diffusion-bond these BPPs, we’re essentially making four different chambers in each one – a product water chamber, an oxygen chamber, a hydrogen chamber and a coolant chamber – and they all become perfectly joined together as one piece of metal, with basically no interfacial contact resistance between each of the layers.” Operation The fuel cell’s optimal performance, in terms of energy efficiency and health, is achieved when the internal environment is maintained at a nominal temperature of around 70 º C. However, the company has also found through testing that the fuel cell can continue operating smoothly when its internal temperature is anywhere from just over 0 º C to just below 100 º C, albeit with some loss of performance at those extremes. The start-up time and configuration of the cell can vary according to Uncrewed Systems Technology | December/January 2023 The BPP’s design is such that four chambers sit between each proton exchange membrane. Beyond the oxidant and hydrogen flow fields are the catalyst and membrane electrode assembly layers We can get a high degree of control over the design of each flow field, to get hydrogen and oxygen to exactly where we want them for each MEA