Spatial Charge Separation in Porphyrin Metal–Organic Frameworks Enables Bifunctional Sites for Overall Water Splitting

Solar-driven overall water splitting provides a route for converting solar energy into chemical fuels, but its realization in porphyrin-based metal-organic frameworks (PMOFs) is limited by the difficulty of coupling reduction and oxidation chemistry within a single framework. Herein, first-principles calculations reveal a spatial separation of the frontier electronic states in two-dimensional M-Cu PMOFs (M = transition metal): the conduction-band edge is predominantly associated with the Cu2(COO)4 paddle-wheel node, whereas the valence-band edge is mainly localized on the porphyrin linker. Combined with site-resolved reaction thermodynamics, this electronic partitioning predicts spatially distinct regions for the hydrogen evolution reaction and oxygen evolution reaction. Systematic screening of 27 M-Cu PMOFs identifies Rh-Cu PMOF as the only candidate satisfying the adopted thermodynamic criteria for both half-reactions, with an idealized upper-bound solar-to-hydrogen efficiency of 15.31% under the adopted spectral model. Sure independence screening and sparsifying operator (SISSO) analysis further identifies total magnetic moment, electronegativity, group number, and d-electron count as physically interpretable descriptors of property variations within this M-Cu PMOF series. These results highlight cooperative linker-node electronic regulation as a computational design principle for porphyrin-based frameworks with spatially differentiated redox functions.