Internal Electric Field Modulation in S-Scheme Heterojunctions via MOF Facet Engineering for Efficient Photocatalytic CO2 Reduction

Abstract Photocatalytic CO2 conversion into high-value-added products represents a promising approach to mitigating global energy demands and environmental problems. S-scheme heterojunctions hold significant potential for photocatalytic CO2 reduction owing to their efficient spatial charge separation and preserved strong redox capabilities, with the internal electric field (IEF) serving as the primary driving force for directional charge transfer. However, achieving precise and rational modulation of the IEF to further boost photocatalytic CO2 conversion efficiency remains a considerable challenge. Herein, we propose a crystal facet engineering strategy to finely tailor the IEF in S-scheme heterojunctions by employing metal−organic frameworks (MOFs) with well-defined exposed facets. A series of NH2-MIL-125@ZnIn2S4 (NM@ZIS) heterojunctions were constructed, and among them, the NM111@ZIS heterojunction interfaced exclusively with the (111) facet was demonstrated to possess the strongest IEF, as unambiguously verified by combined experimental characterization and density functional theory (DFT) calculations. This optimized charge configuration resulted in good photocatalytic CO2 reduction performance, yielding a CO evolution rate of 145.55 μmol·g−1·h−1, substantially outperforming counterparts with mixed or other facet orientations. This work provides a viable pathway for customizing the IEF in S-scheme heterojunctions through MOF crystal facet engineering, offering generalizable insights for the rational design of high-performance photocatalysts.