Tin oxide (SnO₂) represents a major fraction of research for developing solid-state gas sensors. Nevertheless, a detailed insight into the chemical-to-electrical transduction mechanisms between ammonia (NH₃) molecules and this metal oxide is still limited. Here, the adsorption of NH₃ on SnO₂ was examined by density functional theory (DFT) calculations and confronted to experimental data obtained with individual nanowire devices. It was concluded that under real working conditions nonlattice oxygens (O_5c) adsorbed on SnO₂ exhibit a more basic character than lattice bridging oxygens (O_2c), and consequently, they play a key role in the dehydrogenation of NH₃ on SnO₂, with N₂ and H₂O as the main resulting products. The sensing process of ammonia on tin oxide nanowires not only involves physical mechanisms but also has a concomitant chemical nature that requires two molecules of NH₃ for the reaction to take place. Our theoretical modeling reveals why ammonia sensing is competitive to the adsorption of water molecules. As a result, interfering effects in monitoring traces of NH₃ intrinsically occur in humid conditions.
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