Enhanced Charge Transfer in Poly(Heptazine Imide) Synergistically Induced by Donor‐Acceptor Motifs and Ohmic Junctions for Efficient Photocatalytic CO₂ Reduction

Poly(heptazine imide) (PHI) has received widely interest in the photocatalytic CO₂ reduction due to its good crystallinity and complete in-plane structure. However, its poor photo-induced carrier separation and migration efficiency and insufficient active sites results in undesirable photocatalytic CO₂ reduction performance. Herein, we designed and constructed a novel ohmic junction photocatalyst by integrating melamine edge-modified PHI (mel-PHI) with extended π-conjugated system with TiN (TiN/mel-PHI) for enhancing the photocatalytic CO₂ reduction activity. Strikingly, the photocatalytic CO₂ reduction yield of the optimal TiN/mel-PHI is 62.64 μmol g^-1 h^-1, which is 5.6 and 2.8 times higher than PHI (11.26 μmol g^-1 h^-1) and mel-PHI (22.32 μmol g^-1 h^-1), respectively. The superior photocatalytic CO₂ reduction activity is attributed not only to the formation of D-A structure by the introduction of melamine, which extends the π-conjugation system, alters the electronic structure of PHI, and accelerates the charge separation and migration, but also to the induced internal electric field by ohmic junction further enhances the charge separation and migration efficiency. Meanwhile, the synergistic effect of mel-PHI and TiN enriched the electron number of TiN, reducing the CO₂ reduction potential. This work highlights the synergistic enhancement of charge transfer between D-A motifs and ohmic junctions, confirming their potential in optimizing photocatalysts.