Engineering Redox–Transport Balance in Cobalt-Metalated Al-PMOFs for CO2 Photoreduction

Porphyrin metal-organic frameworks (PMOFs) are recognized for their significant potential as photocatalysts active under visible light due to their adjustable structural attributes and extensive π-conjugated porphyrin core. In this study, the photocatalytic efficacy of aluminum-based porphyrin MOFs (Al-PMOFs) modified with four non-noble metals (Co2+, Cu2+, Zn2+, and Ni2+) is systematically examined. Among the evaluated materials, Al-PMOF(Co) exhibited the highest photoactivity toward CO2 reduction to formic acid. Through systematic variation of the cobalt loading (0.25-15 wt %), the 8 wt % incorporation level was identified as the best-performing among those investigated. The photocatalytic activity of Al-PMOF(Co)_8 was 1.6-fold higher than that of pristine Al-PMOF. Theoretical simulations enhanced through an active learning approach identified the critical descriptors governing photocatalytic performance, including band gap characteristics, band edge positions, charge separation, and carrier effective masses under operando conditions. These findings demonstrate the importance of cobalt incorporation for improving charge separation and enhancing photocatalytic CO2 reduction, providing useful guidelines for the rational design of highly efficient photocatalysts for sustainable carbon conversion.