Time-Phase-Controlled Exsolution of FeCoNi Ternary Alloy Nanoparticles on Perovskite Anode Catalyst for Enhanced Dual-Functional Catalysis and Protection in Ammonia-Fueled Protonic Ceramic Fuel Cells

Abstract

Ammonia is a promising carbon-neutral fuel, yet its application in protonic ceramic fuel cells (PCFCs) is hindered by the poor durability and catalytic efficiency of conventional Ni-based anodes. In this study, we present a novel time-phase-controlled exsolution strategy to fabricate a Sr2Fe1.5Mo0.35Co0.1Ni0.05O6-δ (SFMCN) perovskite anode catalytic layer (ACL). This approach enables the in-situ formation of uniformly dispersed FeCoNi ternary alloy nanoparticles, sized between 20 to 40 nm, achieving an exceptionally high triple phase boundary areal density of 182.12 μm μm-2 through reduction-induced phase transformation. The ACL undergoes sequential phase evolution with prolonged reduction, where the Ruddlesden-Popper (R-P) perovskite phase content increases from 61.7 wt.% to 70.8 wt.%, accompanied by an increase in alloy nanoparticle content from 2.6 wt.% to 3.2 wt.%. The optimized PCFC exhibits complete (100%) ammonia decomposition at 700 °C while effectively protecting the Ni-based anode from corrosion. Moreover, it demonstrates superior power retention under ammonia compared to hydrogen, maintaining stable operation for over 100 hours at 650 °C. Density functional theory calculations reveal that the FeCoNi alloy features a tailored electronic structure with enhanced catalytic activity for ammonia decomposition. Additionally, the R-P perovskite phase within the ACL is identified as a potential proton conductor, facilitating effective coupling between the nanoparticles and the Ni-based anode. This study addresses critical challenges in ammonia-decomposing electrocatalysts and advances the development of efficient and durable direct-ammonia PCFCs.