Energy Resiliency Using Reversible Solid Oxide System

Energy generation and storage are critical to achieve energy resiliency. Decoupling fuel storage and power generation increases availability of intermittent renewable energy by storing excess energy and providing sustained power when renewable energy output is low, or grid power is interrupted. Reversible solid oxide cell (rSOC) systems operate in both electrolysis and fuel cell modes to shift renewable power from when it is available to when it is needed, addressing the intermittency of renewable energy, a critical technology area for US Department of Air Force (DAF), and DAF Operational Imperatives to secure resilient basing and power for spacecraft. With the support of DAF Direct to Phase 2 contract FA864924P1033, OxEon is designing, building, and demonstrating a rSOC system to generate electrical power from stored hydrogen gas in fuel cell mode and produce hydrogen fuel from steam in electrolysis mode. The system includes a balance of plant (BOP) and hydrogen compression system that increases the stack-produced H 2 to 5 barg for storage. The rSOC system incorporates a 65-cell stack that generates 1 kW power in solid oxide fuel cell (SOFC) operation with stored H 2 , and produces H 2 with an input of 2 kW e , with a target H 2 production rate of 1.4 kg/ day. System modeling, based on selected BOP components, identified the capability to cycle the system between electrolysis and fuel cell operation with a 15.8 hr initial solid oxide electrolysis cell (SOEC) cycle, followed by repeating 3.4 hr SOFC and 5.3 hr SOEC cycles. The demonstration system combines recent advances in OxEon’s rSOC technology. OxEon’s ruggedized, hermetic SOEC stack can operate at 1.5 to 3 barg pressure which can eliminate the largest and most costly first stage hydrogen compressor. The modestly pressurized stack produced hydrogen can then be compressed to an appropriate storage pressure with a smaller compressor. In a previous project (DOE, contract DE-FE0032105), OxEon operated a 6-cell stack to generate hydrogen at >80% steam conversion, and oxygen above 98.5% purity during pressurized operation. Both hydrogen and oxygen were generated at 3 barg pressure without the use of a pressure vessel. In addition, the test sequence included electrolysis operation at 1 bar differential pressure across anode and cathode that demonstrated substantial robustness of the cell and seal. A redox tolerant fuel electrode allows recovery from accidental oxidation of the Ni-based fuel electrode, which further increases the robustness of the stack. Under the DOE project, a stack test with the redox tolerant fuel electrode exhibited stable performance in multiple redox and thermal cycling, and stable performance in testing for 500 hours in SOEC mode, followed by 300 hours of cycling between SOEC and SOFC tests. Degradation during SOEC operation was 1.8 %/ 1,000 hours, based on a 500 hour test. In general, degradation is non-linear and reduces over time. Investigation is underway to identify contributions to early degradation. System operation benefits from improved performance stability resulting from materials development that targeted stabilizing the air electrode and improving the air electrode barrier layer. Seal materials developed under Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) program enable pressure differential from SOEC stack and its exterior. The stack on Mars successfully operated 16 times, meeting all the operational objectives and producing propellant quality (>99.6% purity) oxygen by electrolyzing Mars atmosphere CO 2 . OxEon specializes in four related energy conversion technologies. They are (1) SOFC for high efficiency generation of electricity using hydrogen and hydrocarbon derived syngas; (2) SOEC for production of hydrogen by electrolyzing steam, and syngas by co-electrolyzing steam and CO2; (3) low energy plasma-based reformer for conversion of gaseous and liquid hydrocarbons to generate syngas; and (4) FT reactor to produce liquid hydrocarbon fuel and wax using syngas as the feed. The overall objective of the company is to develop technologies for transformative cross sector energy conversion to store renewable energy in the form of hydrogen and drop-in transportation fuel. OxEon’s Project EquinOx, supported by the Department of Energy under Award Number DE-EE0011305, will implement a 25manufacturing facility for SOC stacks, 25 MWe annual stack production capacity, scalable to a fully automated GWe facility. A strategy of manufacturing scale up and performance improvement will be implemented to lower the cost of SOE stacks on a per kW basis. Figure 1