Atomically thin two-dimensional (2D) carbon nitride sheets (CNs) are attracting attention in the field of photocatalytic CO2 reduction. Because of the rapid recombination of photogenerated electron–hole pairs and limited more active sites, the photocatalytic efficiency of CNs cannot meet the actual requirements. Here, atomically thin 2D/2D van der Waals heterostructures of metal-free graphdiyne (GDY)/CNs are fabricated through a simple electrostatic self-assembly method. Experimental characterizations along with first-principles calculations show that the introduction of GDY in CNs promoted the transport of photogenerated carriers in the melon chain, thus suppressing the recombination of photogenerated electron–hole pairs. Both in situ FTIR measurements and DFT calculation confirm that the introduced GDY served as the CO2 adsorption site and enhanced the CO2 adsorption capacity of the CNs/GDY heterostructure. Thanks to the 2D/2D van der Waals heterojunction, the optimized CNs/GDY enhances significantly the CO generation rate up to 95.8 μmol g–1 that is 19.2-fold higher than that of CNs. This work provides a viable approach for the design of metal-free van der Waals heterostructure-based photocatalysts with high catalytic activity.

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The low separation efficiency of the photogenerated carrier and the poor activity of the surface redox reaction are the main barrier to further improvement of photocatalytic materials. To address these issues, introducing spin‐polarized electrons in single‐component photocatalytic materials emerged as a promising approach. However, the decreased redox ability of photocarriers in these materials becomes a new challenge. Herein, we mitigate this challenge with a carbon nitride sheet (CNs)/graphene nanoribbon (GNR) composite material that has a van der Waals heterostructures (vdWHs) and spin‐polarized electron properties. Experimental results and theoretical calculations show that the heterostructure has a strong redox ability, high carrier‐separation efficiency, and enhanced surface catalytic reaction. Consequently, the mixed‐dimensional CNs/GNR vdWHs exhibit remarkable performance for H2 and O2 generation as well as CO2 production under visible‐light irradiation without any cocatalyst. The spin‐polarized vdWHs discovered in this study revealed a new type of photocatalytic materials and advanced the development of spintronics and photocatalysis.