High-Volumetric Density Atomic Cobalt on Multishell ZnxCd1–xS 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.