Uncovering the detailed reaction mechanism can provide new insights into modulating the catalytic behavior by junction engineering in photocatalytic CRR materials. However, up to date, no studies have reported photocatalytic CRR over isotype heterojunctions. These encouraging achievements indicate the superior photocatalytic properties of isotype heterojunctions, which are highly desirable for improving the performance of photocatalytic CRR. More recently, a high solar-to-hydrogen conversion efficiency of 1.16% was reported over an isotype heterojunctions consisting of boron-doped and nitrogen-deficient g-C 3N 4. It has been reported that the isotype heterojunctions of rutile-/anatase-TiO 2 and monoclinic/tetragonal BiVO 4 exhibit superior photocatalytic properties. Particularly, due to the similar crystal lattices and electronic structures, isotype heterojunctions exhibit a superior stability, close contact, native compatibility and thus lower potential barrier for charge migration than the heterotype counterparts. This avenue is potentially extended by constructing isotype heterojunctions between two different phases with staggered gaps of an identical substance. As a result of the favorable attributes, enormous efforts are continuously undertaken in the design and investigation of junction photocatalysts for CO 2 photoreduction. The former allows wide light-absorption range, and the latter is ascribed as the synergy between the internal electric field and the band alignment at the interface. These primarily include the narrowed band gaps and particularly the feasibility and effectiveness for the spatial separation and transfer of photogenerated electron–hole pairs. Moreover, several fundamental principles have been identified to rationalize the superiority. The proper design of junction photocatalysts enables superior conversion efficiency. In the past decades, great progress has been made. Light-driven CRR over photocatalysts is one of the most promising conversion technologies since it can proceed under relatively mild conditions, which facilitates its resource utilization. The conversion of CO 2 into value-added fuels and feedstock is increasingly attractive due to the growing urgency to advance a sustainable carbon–neutral economy.

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