A first-principles study of the effect of water on ammonia adsorption and dissociation at the Ni-YSZ interface in SOFC anodes

In this study, first-principles calculations based on density functional theory (DFT) were conducted to investigate the adsorption and dissociation mechanisms of NH 3 and H 2 O at the Ni–yttria-stabilized zirconia (Ni–YSZ) interface, combined with experimental observations of NH 3 decomposition to provide insight into the suppression of NH 3 decomposition by H 2 O in solid oxide fuel cell (SOFC) anodes. The results show that both NH 3 and H 2 O exhibit the strong adsorption energy at the Ni–YSZ interface, suggesting that this interface serves as a highly favorable site for molecular adsorption and leading to competitive adsorption between NH 3 and H 2 O. Experimental findings confirm that H 2 O suppresses NH 3 decomposition, especially at lower temperature. This inhibitory effect is attributed to the comparable dissociation activation energies of the NH 3 and H 2 O molecules at Ni–YSZ interface, enabling H 2 O to compete effectively with NH 3 at the initial dissociation step. Moreover, H 2 O dissociation is more exothermic than that of NH 3 , and the presence of H 2 O shifts the NH 3 dissociation to more endothermic, further inhibiting NH 3 decomposition under low-temperature conditions. NH 3 and H 2 O exhibit site-dependent dissociation behavior, governed by distinct underlying mechanisms—NH 3 dissociation is primarily governed by adsorption strength, following the Brønsted–Evans–Polanyi (BEP) relationship, whereas H 2 O dissociation is influenced by a combined effect of molecular binding and charge accumulation. • H 2 O inhibits NH 3 decomposition in Ni–YSZ anode, especially at lower temperatures. • H 2 O adsorbs strongly to YSZ, limiting NH 3 migration to Ni. • Competitive adsorption and dissociation between H 2 O and NH 3 at reactive sites. • NH 3 dissociation follows BEP relation related to adsorption energy. • H 2 O dissociation involves adsorption strength and charge redistribution.