Steering Catalytic Activity and Selectivity of CO₂ Photoreduction to Syngas with Hydroxy‐Rich Cu₂S@ROH‐NiCo₂O₃ Double‐Shelled Nanoboxes

Simultaneous transformation of CO₂ and H₂ O into syngas (CO and H₂ ) using solar power is desirable for industrial applications. Herein, an efficient photocatalyst based on double-shelled nanoboxes, with an outer shell of hydroxy-rich nickel cobaltite nanosheets and an inner shell of Cu₂ S (Cu₂ S@ROH -NiCo₂ O₃ ), is prepared via a multistep templating strategy. The high performance of Cu₂ S@ROH -NiCo₂ O₃ (7.1 mmol g⁻¹ h⁻¹ for CO; 2.8 mmol g⁻¹ h⁻¹ for H₂ ) is attributed to the hierarchical hollow geometry and p-n heterojunction to promote light absorption and charge separation. Spectroscopic and theoretical analyses elucidate that the ROH -NiCo₂ O₃ surface enhances *CO₂ adsorption and lowers energy barriers for CO₂ -to-CO. Therefore, modulating the hydroxy contents of ROH -NiCo₂ O₃ can achieve broad CO/H₂ ratios from 0.51 to 1.24. This work offers in-depth insights into adjustable syngas photosynthesis and generalized concepts of selective heterogeneous CO₂ photoreduction beyond cobalt-based oxides.