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 CO 2 and H 2 O upcycling to CH 3 OH lies in orchestrating balanced delivery of electrons, protons, and CO 2 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-NH 2 /CoO x /In 2 O 3 catalysts with precisely controlled UiO-66-NH 2 dimensions. PtCu nanoparticles are strategically positioned at the core of light-harvesting UiO-66-NH 2 nanooctahedra to catalyze CO 2 methanolization, while CoO x and In 2 O 3 deposited on the UiO-66-NH 2 outer surface facilitate H 2 O oxidation and amplify upward surface band bending (SBB), respectively. Modulation of UiO-66-NH 2 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 CoO x, as well as between PtCu and the UiO-66-NH 2 outer surface, thereby modulating mass transport distances for protons and CO 2 molecules and their accessibility to PtCu sites. Leveraging this multifaceted size effect, the quaternary catalyst with a moderate UiO-66-NH 2 edge length of 87 nm achieves an optimal balance in electron, proton, and CO 2 supply, delivering a champion CH 3 OH yield of 562.8 μmol g cat –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.