Sandwich-Polarized Heterojunction: Efficient Charge Separation and Redox Capability Protection for Photocatalytic Overall Water Splitting.

Photocatalytic overall water splitting is a potential strategy to address energy crisis and environmental issues. However, it remains a great challenge to design an efficient photocatalyst, which not only possesses large spatial separation of photogenerated electrons and holes (PEH) to suppress recombination, but also can preserve the redox capability to drive the reaction. Herein, we design a new type of sandwich-polarized heterojunction by inserting a polarized semiconductor into the interlayer of the conventional photocatalyst. The inserted sublayer with out-of-plane polarization can induce a large electrostatic potential difference between the top and bottom photocatalytic sublayers. Then, the band edges of the top and bottom sublayers can be shifted to form the type II band alignment. Also, the valence band maximum and conduction band minimum will be located on different photocatalytic sublayers to facilitate the spatial separation of PEH. Simultaneously, different from the conventional type II heterojunction that reduces the redox capability, the electrostatic potential difference also acts as an auxiliary booster to offset the reduced redox potential of PEH. Taking the CN/InSe/CN heterojunction as an example, the polarized InSe effectively promotes the interface transfer of PEH in 1-5 ps and extends the lifetime of PEH to ∼186 ns, which is about six times that of bilayer CN. Simultaneously, the redox power of CN is well preserved. Our work offers a promising scheme to advance the photocatalytic overall water splitting.