Boosting Electron-Hole Charge Separation in CO₂ Photoreduction through Fluoroporphyrin-Linked Nickel(II)-Acetylide Frameworks

Abstract

Metal-acetylide frameworks (MAFs) have emerged as efficient catalysts due to their unique d-π orbital hybridization between transition metal ions and sp-hybridized carbons in multi-acetylenic ligands, forming robust metal-bis(acetylide) moieties. Herein, we report the synthesis of a novel nickel(II)-acetylide framework (H₂TFPP-Ni-AF) featuring well-defined ─C≡C─Ni(PBu₃)₂─C≡C─ (where Bu = ─CH₂CH₂CH₂CH₃) catalytic sites, which demonstrates remarkable photocatalytic CO₂-to-CO conversion rate. The catalyst achieves a CO yield of 52.64 mmol g⁻¹, an average production rate of 13.16 mmol h⁻¹ g⁻¹, and 97.9% selectivity over a 4-h reaction, substantially outperforming its metal-free analogue (H₂TFPP-GDY). Mechanistic insights from the combined experimental and theoretical studies reveal that the enhanced performance stems from the synergistic interplay between Ni^II-bis(acetylide) moieties, which facilitate CO₂ adsorption and activation, and fluoroporphyrin units, which enhance light-harvesting and charge-transport capabilities, leading to bandgap narrowing, improved electron-hole charge separation, and reduced energy barrier for *COOH intermediate formation. Additionally, the electron-deficient fluoroporphyrin acts as an electron acceptor, extracting photogenerated electrons from the Ni(PBu₃)₂ moieties and further promoting charge separation during the photocatalytic CO₂ reduction reaction (CO₂RR). This work provides a rational design strategy for optimizing MAF-based photocatalysts toward solar-driven CO₂ conversion.

Keywords

charge separation / fluoroporphyrin / nickel(II)-acetylide frameworks / photocatalytic CO₂ reduction reaction

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