Confinement Effects on the Rh ^III Cp* / Polyoxometalate System in Photochemical CO ₂ Reduction Reactions: Porous Organic Polymer Versus Metal–Organic Framework

ABSTRACT The incorporation of polyoxometalates (POMs) into transition metal‐based photosystems has emerged as an effective strategy to boost photocatalytic performances for CO 2 and water reduction into renewable energy vectors. Despite significant progress in designing {POM, porous host} composites containing isolated catalytically active metal complexes, the atomic‐level understanding of their structure‐function relationship remains limited. Here, we investigate the effect of encapsulated [PW 12 O 40 ] 3− POMs on the photocatalytic CO 2 reduction (CRR) performance of a Rh‐catalyst, namely the pentamethylcyclopentadienyl rhodium(III) (Rh III Cp*), immobilized in porous organic polymers (POPs) and compare it with the Rh III Cp*‐functionalized UiO‐67 MOF. While the incorporated POM enhances overall activity in both systems, (POM,Rh III Cp*)@POPs show a stronger shift in selectivity toward the hydrogen evolution reaction (HER). By combining the high sensitivity of dynamic nuclear polarization enhanced NMR spectroscopy with atomistic computational modelling techniques, we elucidate the POMs’ location, speciation and host‐guest interactions within the amorphous POP matrices. The results reveal that in presence of solvent, electrostatic anchoring of POMs to the POP's backbone promotes the accumulation of HTEOA + proton donors near Rh active sites, favoring selectively HER up to 240% of the initial activity of catalysts without POM incorporated. The latter contrasts with the confinement of the POM within the narrower pores of UiO‐67, limiting POM···HTEOA + interactions, thus enhancing both CRR and HER activity.