Engineering Single Ni Sites on 3D Cage-like Cucurbit[n]uril Ligands for Efficient and Selective CO2 Photocatalytic Reduction

Abstract

Solar-driven CO₂ selective reduction with high conversion is a challenging task yet holds immense promise for both CO₂ neutralization and green fuel production. Enhancing CO₂ adsorption at the catalytic centre can trigger a highly efficient CO₂ capture-to-conversion process. Herein, we introduce cucurbit[n]urils (CB[n]), a new family of molecular ligands, as a key component in the creation of a 3D cage-like metal (nickel, Ni)-complex molecular co-catalyst (CB[7]-Ni) for photocatalysis. It exhibits an unprecedented CO yield rate of 72.1 μmol ⋅ h^-1 with a high selectivity of 97.9 % under visible light irradiation. To verify the origin of the carbon source in the products, a straightforward isotopic tracing method is designed based on tandem reactions. The catalytic process commences with photoelectron transfer from Ru(bpy)₃ ²⁺ to the Ni²⁺ site, resulting in the reduction of Ni²⁺ to Ni⁺. The locally enriched CO₂ molecules in the cage ligand CB[7] undergo selective reduction by the Ni⁺ nearby to form CO product. This work exemplifies the inspiring potential of ligand structure engineering in advancing the development of efficient unanchored molecular co-catalysts.

Keywords: 3D ligand; CO2 reduction; Cucurbit[n]uril; molecular co-catalyst; photocatalysis.