High-Volumetric Density Atomic Cobalt on Multishell Zn_<i>x</i>Cd_1–<i>x</i>S Boosts Photocatalytic CO₂ Reduction

The volumetric density of the metal atomic site is decisive to the operating efficiency of the photosynthetic nanoreactor, yet its rational design and synthesis remain a grand challenge. Herein, we report a shell-regulating approach to enhance the volumetric density of Co atomic sites onto/into multishell Zn_xCd_1-xS for greatly improving CO₂ photoreduction activity. We first establish a quantitative relation between the number of shell layers, specific surface areas, and volumetric density of atomic sites on multishell Zn_xCd_1-xS and conclude a positive relation between photosynthetic performance and the number of shell layers. The triple-shell Zn_xCd_1-xS-Co₁ achieves the highest CO yield rate of 7629.7 μmol g^-1 h^-1, superior to those of the double-shell Zn_xCd_1-xS-Co₁ (5882.2 μmol g^-1 h^-1) and single-shell Zn_xCd_1-xS-Co₁ (4724.2 μmol g^-1 h^-1). Density functional theory calculations suggest that high-density Co atomic sites can promote the mobility of photogenerated electrons and enhance the adsorption of Co(bpy)₃²⁺ to increase CO₂ activation (CO₂ → CO₂* → COOH* → CO* → CO) via the S-Co-bpy interaction, thereby enhancing the efficiency of photocatalytic CO₂ reduction.