Metal Halide Perovskite-based Heterojunctions for Green Ammonia Production: Material Engineering and Mechanistic Features

Designing innovative photocatalysts for nitrogen photofixation is becoming crucial for the development of carbon neutral ammonia production. Metal halide perovskites (MHPs) have been demonstrated to be effective materials to run a wide range of photoredox reactions mediated by solar light. Herein, we develop an innovative heterojunction based on the vacancy-ordered double perovskite Cs2SnBr6 and carbon nitride nanosheets and demonstrate its ability in running the nitrogen photofixation reaction to produce ammonia. We explore the full compositional range for the Cs2SnBr6/g-C3N4 system and identify an optimal range providing an ammonia evolution rate up to 260 μmol g-1 h-1, the highest value reported to date for a MHP-containing catalyst. Mechanistic insight into the photofixation reaction promoted by the heterojunction was obtained through a combination of advanced spectroscopy and computational modelling. Efficient ammonia production stems from an effective charge transfer from the perovskite to the nitrogen vacancies on the carbon nitride enabled by the absence of self-trapped excitons in Cs2SnBr6 which also provides additional reactive sites through bromide vacancies. This work, reporting an efficient MHP-based heterojunction for nitrogen photofixation and a clear definition of the underlying reaction mechanism, provides a catalyst design strategy that may pave the way for sustainable ammonia production.