Direct and Sustainable Ammonia Synthesis from Air and Water with Sulfur-Deficient MoS₂ Piezocatalysts.

Abstract

Eco-friendly ammonia (NH₃) production is critical for advancing sustainable agriculture and industry. This study introduces a sustainable, cleaner approach using MoS₂ nanoflowers (NFs) to synthesize NH₃ directly from water and air without the need for sacrificial agents. The advanced design leverages double sulfur vacancies (V2s) in MoS₂ NFs (V2s-MoS₂ NFs) and their piezoelectric properties, achieving a noteworthy production efficiency of 8374.8 ± 140.1 μmol L^-1 g^-1 h^-1 (absolute production rate of 0.84 ± 0.01 μmol h^-1). This outperforms most existing photocatalysts and piezocatalysts and rivals advanced electrocatalysts. The catalyst demonstrated exceptional stability, producing 36.55 mmol L^-1 g^-1 (equivalent to an absolute yield of 3.655 μmol) with N₂ and 26.03 mmol L^-1 g^-1 (equivalent to an absolute yield of 2.603 μmol) with air over 8 h. In situ Raman spectroscopy revealed intensifying peaks at ∼819 and 993 cm^-1 under N₂ gas, attributed to Mo-N stretching vibrations. Additionally, in situ diffuse reflectance infrared Fourier-transform spectroscopy showed N₂ adsorption configurations, including side-on adsorption, indicative of N≡N bond elongation on the catalyst surface. Density functional theory calculations corroborated these findings, illustrating how unpaired Mo d orbital electrons near sulfur vacancies activate N₂ dissociation via backdonation to N₂'s antibonding π orbitals. This research highlights the transformative potential of piezocatalytic systems for nitrogen reduction reactions using atmospheric N₂ and water, providing a basis for sustainable energy solutions.