Exploring the Feasibility of Using Ammonia as a Sulfur Remover to Restore Sulfur-Poisoned Ni-Based Anodes in Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) offer an alternative power generation method to conventional combustion engines, capable of utilizing hydrocarbons or any hydrogen-containing fuels efficiently, cleanly, and quietly. JP-8 is a common logistical fuel that can power SOFCs after proper reforming. However, the high sulfur (S) content in JP-8 presents a challenge to SOFC operation, as it poisons Ni-based anodes, causing performance degradation. Herein, we study the technical feasibility of restoring the functionality of S-poisoned Ni-based anodes by ammonia. We hypothesize that ammonia-derived H2 removes sulfur species in the poisoned Ni-based anode by reacting with S to form H2S and thus freeing Ni. The experiment was conducted using an anode-supported tubular SOFC operated in cyclic mode between JP-8 reformate containing 300 ppm of H2S and pure ammonia. The results show that the cell exhibits a significant performance drop and S accumulation on the anode surface when operating with the S-containing JP-8 reformate. After ammonia exposure, the cell performance mostly recovers with no trace of S found on the anode surface. However, the overall cell performance experiences degradation upon repeated S poisoning and “ammonia cleaning” cycles. Post-test analysis reveals that the Ni-based anode suffers significant Ni coarsening and migration, which we hypothesize are caused by the decomposition of Ni sulfide and the ammonia–Ni reaction during the “ammonia cleaning” cycle.