Defects in MOFs for Photocatalytic Water Reduction to Hydrogen Generation: From Fundamental Understanding to State-of-Art Materials

Metal-organic frameworks (MOFs) are highly studied for solar H₂ production from H₂O due to their abundant active sites and open pore channels. Titanium (Ti) and Zirconium (Zr) MOFs are particularly noted for their stability and optoelectronic properties, resembling conventional metal oxide semiconductors. These MOFs allow molecular-level tuning to alter optoelectronic properties, creating opportunities to enhance catalytic activity. Introducing defects in the MOF's structure is a versatile strategy for modifying molecular topology, morphology, and optical and electronic properties. This review compiles essential methods for synthesizing defect-oriented MOFs, discussing characterization techniques and their structural and electronic modifications to boost catalytic activity. It also highlights the connection between photocatalytic H₂ production and MOF properties, exploring strategies to address current limitations using defective Ti and Zr-based MOFs. Additionally, the role of machine learning (ML) in predicting MOF properties for faster material discovery and optimization is emphasized. This review aims to identify challenges and propose ideas for designing future defect-oriented MOF photocatalysts.