Nafion-Assisted Noncovalent Assembly of Molecular Sensitizers and Catalysts for Sustained Photoreduction of CO₂ to CO

Abstract

The efficient coupling of light absorbers with catalysts is the most critical step in the multielectron transfer process for CO2 conversion. Here a heterogenized photoconversion system consisting of noncovalent assembly is tested and proposed. Nafion (Nf) polymer is employed as a simple and robust platform that couples the light absorber (Ru-(bpy)32+: RuL) and the catalyst (fac-Re(bpy)(CO)3Cl: Re(I)) without making any chemical linkage between them to drive the reductive conversion of CO2 to CO. The results clearly show that the ternary Re(I)-RuL-Nf system exhibits higher photoconversion of CO2 and higher photostability than those of the homogeneous Re(I)-RuL system without Nf. Nf polymer backbone provides sulfonate ionic exchange sites that tightly bind cationic RuL through electrostatic attraction. The Nf-bound RuL sensitizers hinder the destructive self-sensitized reaction but enhance the chance of bimolecular electron transfer from the excited RuL to Re(I), which was confirmed by time-resolved spectroscopic analysis. The total turnover number (TON) of produced CO after 20 h reached 454 in the Re(I)-RuL-Nf system (vs TON 110 in Re(I)-RuL), which demonstrated the essential role of Nf in the photoconversion process.