Preventing molecular catalyst aggregation in Z-scheme photocatalyst for unassisted CO₂ reduction

Due to stringent thermodynamic and electronic requirements, photocatalytic CO₂ reduction (PCR) remains a significant challenge, particularly in the absence of sacrificial agents and noble metal cocatalysts—a process referred to as unassisted photocatalysis. In this study, we report a CuPc/α-MnO₂-based Z-scheme photocatalyst capable of performing PCR without the need for any sacrificial agents or precious metal cocatalysts. A major obstacle in such systems is maintaining a highly dispersed CuPc assembly on the support material, as aggregation typically leads to reduced activity. To overcome this, we introduce a phosphate-modulated hydrogen bonding strategy that effectively prevents CuPc aggregation on the α-MnO₂ scaffold. Combined theoretical and experimental investigations reveal that the phosphate-bridged strong interfacial coupling, along with enhanced charge transfer to catalytically active sites, facilitates efficient CO₂ activation. The well-dispersed cationic Cu^2 + centers in CuPc act as the primary sites for CO₂ adsorption and multi-electron reduction, further contributing to the reaction performance. The thermodynamic and kinetic mechanisms underlying unassisted PCR on the CuPc/α-MnO₂ system are elucidated through density functional theory (DFT) calculations, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and photoelectrochemical measurements. This work provides valuable insights for the rational design of next-generation photocatalysts for solar-driven CO₂ conversion.