Modulating Surface Band Bending and Redox Site Spacing in Metal–Organic Frameworks for Boosting Methanol Photosynthesis from CO ₂ and H ₂ O

A primary challenge in photocatalytic CO2 and H2O upcycling to CH3OH lies in orchestrating balanced delivery of electrons, protons, and CO2 molecules to reactive sites. Here, we present an innovative metal–organic framework (MOF) size engineering strategy that addresses this challenge through the rational construction of PtCu@UiO-66-NH2/CoOx/In2O3 catalysts with precisely controlled UiO-66-NH2 dimensions. PtCu nanoparticles are strategically positioned at the core of light-harvesting UiO-66-NH2 nanooctahedra to catalyze CO2 methanolization, while CoOx and In2O3 deposited on the UiO-66-NH2 outer surface facilitate H2O oxidation and amplify upward surface band bending (SBB), respectively. Modulation of UiO-66-NH2 size enables simultaneous tuning of both the SBB degree and PtCu positioning relative to the space charge region, thereby governing the catalyst’s charge separation efficiency and PtCu’s electron acceptance capability. Concurrently, size variation fine-tunes the spacing between PtCu and CoOx, as well as between PtCu and the UiO-66-NH2 outer surface, thereby modulating mass transport distances for protons and CO2 molecules and their accessibility to PtCu sites. Leveraging this multifaceted size effect, the quaternary catalyst with a moderate UiO-66-NH2 edge length of 87 nm achieves an optimal balance in electron, proton, and CO2 supply, delivering a champion CH3OH yield of 562.8 μmol gcat–1 h–1 with 93.3% selectivity. This MOF size engineering strategy establishes a powerful paradigm for developing efficient artificial photosynthetic systems through the synergistic manipulation of SBB and redox site spacing.