Abstract: Recently, the noble metal Au has been widely applied as the cocatalyst for improving the photocatalytic reduction of CO₂. However, the metallic Au exhibits weak adsorption strength towards CO₂ due to its intrinsic electronic structure with d-orbitals fully filled, thus limiting the activation and reduction of CO₂. To address this issue and maximize the photoreduction of CO₂, herein we have designed Au@CZS@MO-400 triple-shelled hollow nanospheres by depositing Cd_0.7Zn_0.3S (CZS) on the outer surface of the MO-400 (MnO₂ annealed at 400 °C) hollow nanospheres and then Au nanoparticles on the CZS surface. It is manifested that the resultant 3%Au@CZS@MO-400 achieves a remarkably boosted photoreduction of CO₂ with the CO/CH₄ yield rates as high as 68.25/12.42 µmol g^-1 h^-1, increased by 3.7/1.5 times over MO-400 and 12.9/1.5 times over CZS. The combined analyses from X-ray photoelectron spectroscopy and density functional theory calculations confirm the creation of electron-deficient Au^δ+ active sites by modulating their electron configuration by CZS, consequently decreasing the CO₂-Au antibonding-orbital occupancy to reinforce the adsorption strength of CO₂ onto the Au active sites and in turn boost the photoreduction of CO₂. Moreover, it is demonstrated that the Au@CZS@MO-400 hollow nanospheres are quite efficient for supplying the Au cocatalyst with photoelectrons for CO₂ reduction reactions due to the good energy band matching, unique hollow structure and high electron spin polarization of MO-400. This work provides important guidance for understanding and modifying photocatalysts to maximize their photoreduction of CO₂.

Key words: Au@CZS@MO-400 hollow nanospheres, Au cocatalyst, CO₂-Au adsorption strength modification, Spin polarization of MO-400, Photoreduction of CO₂