Light-driven ammonia synthesis under mild conditions using lithium hydride.

Area of Science:

• Materials Science
• Photochemistry
• Catalysis

Background:

• Photon-driven chemical processes often rely on semiconductors like oxides, nitrides, and sulfides.
• These materials suffer from limited photo-conversion efficiency due to charge carrier recombination.

Purpose of the Study:

• To investigate the photolysis of lithium hydride (LiH) under ultraviolet (UV) illumination.
• To explore the potential of photon-generated electrons in LiH for reversible chemical transformations at lower temperatures.
• To demonstrate the application of light-activated LiH in photocatalytic ammonia synthesis.

Main Methods:

• Subjecting lithium hydride to ultraviolet illumination to induce photolysis.
• Characterizing the generated photon-generated electrons in hydrogen vacancies (F centres).
• Conducting reversible dehydrogenation and rehydrogenation experiments at room temperature.
• Investigating the cleavage of the N≡N triple bond and subsequent N-H bond formation under mild conditions.
• Performing photocatalytic ammonia formation using a N2/H2 mixture with LiH under near-ambient conditions.

Main Results:

• UV illumination of LiH leads to photolysis, generating long-lived electrons in hydrogen vacancies (F centres).
• Photon-driven dehydrogenation and dark rehydrogenation of LiH are achieved reversibly at room temperature, significantly lower than thermal processes.
• Light-activated LiH effectively cleaves the N≡N triple bond, facilitating N-H bond formation.
• Photocatalytic ammonia formation from N2/H2 is demonstrated at near-ambient conditions using LiH.

Conclusions:

• Lithium hydride serves as a novel material for light-driven chemical processes, utilizing F centres for charge carrier separation.
• The reversible, low-temperature dehydrogenation/rehydrogenation of LiH offers an efficient alternative to traditional thermal methods.
• Light-activated LiH shows promise for efficient photocatalytic ammonia synthesis under mild conditions, contributing to advancements in light harvesting and conversion technologies.