Emerging Stacked Photocatalyst Design Enables Spatially Separated Ni(OH) 2 Redox Cocatalysts for Overall CO 2 Reduction and H 2 O Oxidation.

Construction of photocatalytic systems with spatially separated dual cocatalysts is considered as a promising route to modulate charge separation/transfer, promote surface redox reactivities, and prevent unwanted reverse reactions. However, past efforts on the loading of spatially separated double-cocatalysts are limited to hollow structured semiconductors with inner/outer surface and monocrystalline semiconductors with different exposed facets. To overcome this limitation, herein, enabled by a unique stacked photocatalyst design, a facile and versatile strategy for spatial separation of redox cocatalysts on various semiconductors without structural and morphological restriction is demonstrated. The smart design begins with the deposition of light-harvesting semiconductors on reduced graphene oxide (rGO) nanosheets, followed with the coverage of Ni(OH) 2 outer layer. The ternary photocatalysts exhibit superior activities and stabilities of H 2 O oxidation and selective CO 2 -to-CO reduction, remarkably surpassing other counterparts. The origin of the enhanced performance is attributed to the synergistic interplay of rGO@Ni(OH) 2 reduction cocatalysts surrounding the semiconductors and Ni(OH) 2 oxidation cocatalysts directly supported by the semiconductors, which mitigates the charge recombination, supplies highly active and selective sites for overall reactions, and preserves the semiconductors from photocorrosion. This work presents a new approach to regulating the position of dual cocatalysts and ameliorating the net efficiency of photoredox catalysis.