Designing an Ammonia Compatible SOFC System

Ammonia (NH3) as a fuel in Solid Oxide Fuel Cell (SOFC) systems for marine applications is a promising approach towards carbon-neutral power generation. Ammonia offers distinct advantages over liquefied hydrogen in terms of handling, storage, and existing distribution infrastructure.

In single cell testing, ammonia has been recognized as a potential fuel for SOFC stacks, demonstrating comparable performance to other fuels such as pure hydrogen and natural gas-based reformates. The nickel containing fuel electrodes of fuel cells, facilitate the decomposition of ammonia feed into nitrogen and hydrogen. Hydrogen is then utilized as a fuel for the power generating electrochemical reaction.

However, challenges arise at the stack level when using ammonia, particularly concerning the use of state-of-the-art steel grades as interconnect plate materials. The high-temperature decomposition of ammonia generates highly reactive N3- ions, leading to nitridation reactions that degrade steel structures, impacting electrode contacts, and potentially resulting in significant performance losses and mechanical cracking of cells.

This study introduces three approaches aimed at advancing the design and development of an ammonia compatible SOFC system. Ex-situ material testing was conducted to assess the material tolerances of common metals used in SOFC systems. The results provide insights for material selection and component development. Secondly, to gather comprehensive data on stack durability and degradation in an ammonia-containing environment, stack-level performance testing was performed using simulated pre-cracked ammonia feeds as the fuel for a 350 W SOFC short stack.

Lastly, ensuring sufficient pre-cracking of ammonia is crucial for maintaining the durability of ammonia fueled SOFCs, as high concentrations of raw ammonia can lead to shortened lifespans. Thus, performance mapping of multi-fuel processing capable nickel catalyst was done at various temperatures. This led to the determination of optimal operating conditions for the highly endothermic ammonia cracking reaction, which could be sustained by the excess heat from the SOFC system.

This study combines laboratory-scale experimental results from ex-situ material testing, stack-level durability experiments, and catalyst performance mapping for the cracker unit. These findings establish design parameters for the development of an upscaled ammonia compatible SOFC system.