Design and structure–function interplay in covalent organic frameworks for photocatalytic CO2 reduction

The escalating global energy demands and the need to alleviate the rapid rise in greenhouse gases have led to colossal interest in designing efficient catalytic systems for photocatalytic CO₂ reduction. While inorganic semiconductors have been the frontrunners for a long time, porous photocatalysts, particularly covalent organic frameworks (COFs), are gaining traction due to their atomically precise structures, enabling tuning their structural and chemical properties. Designed using the principles of reticular chemistry, the building units of COFs can be modulated to incorporate catalytically active sites periodically using robust covalent bonds to endow them with high efficiency, selectivity, and stability. Unlike the non-porous congeners, COFs, with their high porosity and precisely defined pore channels, allow for quicker diffusion of substrates and products, enabling the utilization of deeply buried photocatalytic sites. Our approach is to comprehend the significant roadblocks that must be overcome for designing state-of-the-art catalysts for photocatalytic CO₂ reduction. Building upon that, we highlight the key strategies devised to design COF-based CO₂RR photocatalysts. A fundamental understanding of the structure-property relationship is quintessential for utilizing the precision of COF chemistry for developing next-generation materials combining activity, selectivity, and efficiency in a single system. Throughout this review, we have taken a closer look at how the critical design aspects and molecular engineering reciprocate towards augmenting the bulk photocatalytic properties of efficiency and selectivity. Understanding molecular engineering and structure-property relationships will be conducive to developing sophisticated systems to solve global crises in this burgeoning area of research.