Steering Catalytic Activity and Selectivity of CO 2 Photoreduction to Syngas with Hydroxy-Rich Cu 2 S@R OH -NiCo 2 O 3 Double-Shelled Nanoboxes.

Simultaneous transformation of CO 2 and H 2 O into syngas (CO and H 2 ) 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 Cu 2 S (Cu 2 S@R OH -NiCo 2 O 3 ), is prepared via a multistep templating strategy. The high performance of Cu 2 S@R OH -NiCo 2 O 3 (7.1 mmol g -1  h -1 for CO; 2.8 mmol g -1  h -1 for H 2 ) 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 R OH -NiCo 2 O 3 surface enhances *CO 2 adsorption and lowers energy barriers for CO 2 -to-CO. Therefore, modulating the hydroxy contents of R OH -NiCo 2 O 3 can achieve broad CO/H 2 ratios from 0.51 to 1.24. This work offers in-depth insights into adjustable syngas photosynthesis and generalized concepts of selective heterogeneous CO 2 photoreduction beyond cobalt-based oxides.