Effects of water on the degradations in the Ni-YSZ anode of the direct ammonia solid oxide fuel cells

Direct ammonia solid oxide fuel cells (DA-SOFCs) are promising next-generation energy conversion devices. Despite their possibilities, the electrochemical performance of DA-SOFCs degrade severely over long-term operation. However, the degradation mechanisms are still unveiled. Here, we reveal that the degradations of DA-SOFCs are significantly initiated by the presence of the water, which is the by-product of the SOFC operation, inside the fuel electrode. We measured the stability of the DA-SOFCs by varying the fuels and water partial pressure in the fuel. Thorough surface characterizations verified that Ni becomes favorable for oxidation when ammonia is present in the water, resulting in a reduction of the catalyst reactivity for NH₃ decomposition and electric conductivity. Furthermore, we conducted a density functional theory calculation and found that N* adsorbed onto Ni decomposed from NH₃ facilitates the H₂O decomposition and results in nickel oxidation.