Engineering van der Waals Heterojunctions Within a 2D Hydrogen-Bonded Organic Framework for Boosting CO2 Electroreduction.

Unlike conventional strategies that regulate charge transport in framework electrocatalysts by modifying covalent skeletons or compositions, we demonstrate efficient directional electron transfer by constructing interlayer van der Waals donor-acceptor (D-A) heterojunctions within a hydrogen-bonded organic frameworks (HOFs). The porphyrin-based HOF, PFC-45-Co, is assembled from electron-donating 5,10,15,20-tetra(4-carboxyphenyl)porphyrin (Co-TPyP) and electron-accepting cobalt 5,10,15,20-tetra(4-carboxyphenyl)porphyrin (Co-TCPP) through strong O─H···N hydrogen bonds, while periodic alternating interlayer π-π stacking generates vertical D-A heterojunctions. Mechanistic studies show that close π-π contacts enable through-space charge transport, and the D-A energy offset drives electron transfer from Co-TPyP to Co-TCPP, producing electron-enriched Co-TCPP sites that promote CO2 activation and suppress hydrogen evolution. As a result, PFC-45-Co outperforms the single-component HOF PFC-72-Co in both neutral and acidic media. In neutral electrolyte, PFC-45-Co delivers a CO Faradaic efficiency (FECO) of 98.4% at -0.9 V versus reversible hydrogen electrode (vs. RHE) and a CO partial current density (jCO) of 31.3 mA cm-2 at -1.2 V versus RHE. In acidic media, it maintains FECO values of 92%-99% and achieves jCO of 111.1 mA cm-2 at -1.6 V versus RHE. This work establishes interlayer van der Waals D-A heterojunctions as an effective motif for regulating charge transfer in HOF electrocatalysts.