NEXTECH MATERIALS, LTD. — Department of Defense SBIR Phase II: OSD13-EP4

Description

Small unmanned aerial systems (S-UAS), unmanned ground systems (UGS), vehicle auxiliary power units (APU), and mobile power generation units require high efficiency power systems capable of operating on logistically available fuels (JP-8, diesel) to enable long endurance operation.In particular, S-UASs in the Group 2 (2155 lbs)/Group 3 (<1,320 lbs) range and UGSs such as the Battlefield Extraction-Assist Robot (BEAR) have a critical need for high efficiency, reliable propulsion system options capable of operation on logistically available fuels.SOFC-based systems have shown promise to meet these needs, with the potential for 30% - 45% thermal efficiency and 1000s of hrs of operational life, compared to < 20% thermal efficiency and 100s of hr of operational life for baseline internal combustion (IC) engine-based propulsion systems within this size class.The main drawback is the lower system-level power density (~100 W/kg compared to ~1000 W/kg for a typical IC engine), which limits the applicability of such systems.For a typical SOFC-based system, the stack represents 30 - 40% of the system weight, assuming a stack power density of 200-300 W/kg.If the stack power density is increased to 5001000 W/kg, this would facilitate a 2X-4X increase in the system-level power density (i.e. 200400 W/kg).This, when combined with the increased fuel efficiency, would enable an SOFC-based propulsion system to meet and/or exceed IC engine performance [1].For example a 200 W/kg SOFC-based propulsion system at 30% efficiency would have comparable endurance to 1000 W/kg IC engine-based system at 20% efficiency, with the potential for increased reliability and operational lifetime.A number of SOFC concepts have been demonstrated at the button cell level, such as low-temperature (LT)-SOFCs [2], metal-supported SOFCs [3], or others; which have the potential to meet these power density goals.The main challenge is exploring the feasibility of scaling up these novel concepts to the stack level while maintaining the same level of power density.For example, LT-SOFCs which have been demonstrated at ~2W/cm2 on the cell level are projected to produce a stack at ~3000W/kg.This projection, though, does not take into account the many issues which can lead to efficiency losses at the stack level, such as: interconnect resistance, interfacial gradients, fuel utilization, etc.The focus of this topic is to demonstrate the scalability of the novel cell-level technology to the larger area cell level (> 150 cm2 active area) in the Phase I and then to the stack level (500W3 kW) in the Phase II in order to determine the feasibility for integration into a complete SOFC power system.There is a particular interest in potential stack technologies which prove to be flexible to fuel reformate composition and tolerant to fuel impurities, such as sulfur content.