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

Abstract

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.