Hydroxyl-Modified C₃N₄-Ni Nanosheets Enhance Photocatalytic CO₂ Methanation

Hydroxyl-Modified C₃N₄-Ni Nanosheets Enhance Photocatalytic CO₂ Methanation

摘要

【Purposes】 In photocatalytic CO₂ reduction reaction, since the electron transfer efficiencies of CH₄ and CO are close and their thermodynamic properties are similar, achieving high electron selectivity for CH₄ still faces significant challenges. 【Methods】 In this study, a single-atom Nidoped C₃N₄ catalyst（CN-Ni） was first synthesized and then hydroxyl-modified to obtain hCN-Ni through the hydrothermal method. 【Results】 Experimental results show that the hydroxyl-modified hCN-Ni catalyst exhibits excellent CO₂ reduction performance, with CO and CH₄ generation rates of 22 and 3.3 µmol·g^-1·h^-1, respectively, and the CH₄ electron selectivity reaches 37.5%. The remarkable performance enhancement stems from the synergistic effect of hydroxyl modification and Ni monoatoms. On one hand, the introduction of hydroxyl groups enhances the hydrophilicity of the catalyst surface, and promotes the adsorption of water molecules as well as the formation of a local waterrich microenvironment, while its asymmetric steric hindrance effectively inhibits the recombination of photogenerated carriers; On the other hand, the dispersed Ni monoatoms on the surface of hCN-Ni serve as active centers for CO₂ adsorption and activation, and protons enriched on the hydroxyl-modified surface can be rapidly transferred to these Ni active sites, thus significantly facilitating the hydrogenation of CO₂ to CH₄.

Abstract

Purposes In photocatalytic CO₂ reduction reaction, since the electron transfer efficiencies of CH₄ and CO are close and their thermodynamic properties are similar, achieving high electron selectivity for CH₄ still faces significant challenges. Methods In this study, a single-atom Ni-doped C₃N₄ catalyst (CN-Ni) was first synthesized and then hydroxyl-modified to obtain hCN-Ni through the hydrothermal method. Results Experimental results show that the hydroxyl-modified hCN-Ni catalyst exhibits excellent CO₂ reduction performance, with CO and CH₄ generation rates of 22 and 3.3 µmol·g^-1·h^-1, respectively, and the CH₄ electron selectivity reaches 37.5%. The remarkable performance enhancement stems from the synergistic effect of hydroxyl modification and Ni monoatoms. On one hand, the introduction of hydroxyl groups enhances the hydrophilicity of the catalyst surface, and promotes the adsorption of water molecules as well as the formation of a local water-rich microenvironment, while its asymmetric steric hindrance effectively inhibits the recombination of photogenerated carriers; On the other hand, the dispersed Ni monoatoms on the surface of hCN-Ni serve as active centers for CO₂ adsorption and activation, and protons enriched on the hydroxyl-modified surface can be rapidly transferred to these Ni active sites, thus significantly facilitating the hydrogenation of CO₂ to CH₄.

Key words

CO₂ reduction / hydroxyl groups / electron selectivity of CH₄ / H₂O adsorption