Mechanistic modulation of porous framework materials and molecular clusters for photocatalytic ammonia synthesis: Recent advancements, challenges and future prospects

Photocatalytic nitrogen (N₂) fixation provides a cost-effective, environmentally friendly, and efficient method for producing ammonia (NH₃), which is utilized in agriculture, energy storage, and the production of zero-carbon fuels for transportation. Recently, porous framework materials (PFMs), including metal organic frameworks (MOFs), porous coordination polymers (PCPs), covalent organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs), and zeolites as well as molecular clusters/polyoxometalates (POMs), have emerged as promising materials for the photofixation of N₂, attributed to high surface areas, configurable structures, and unique active sites, which aid N≡N triple bond activation and facilitate efficient electron transfer. The synthesis methods, design strategies focusing on electronic/surface modulation, and photocatalytic N₂-fixation performance of PFMs and POMs are summarized. Additionally, the reaction mechanism, charge-carrier kinetics, and thermodynamics, particularly those elucidated by advanced characterization techniques, are emphasized. Challenges and future directions emphasizing the integration of renewable energy sources, advances in catalyst stability, and scalability are also discussed. This review aims to design and develop advanced organic-inorganic materials for N₂ photofixation, to facilitate the practical implementation of photocatalytic NH₃ synthesis.