Proton-Coupling Electron Transfer Kinetics Modulation via Substitution Isomerism of Amino Groups in MOFs to Switch CO₂ Photoreduction Pathways from HCOOH to CH₃COOH.

Abstract

Selective photoreduction of CO₂ into high-value C2 products is highly desirable but challenging due to the high-energy-barrier C-C coupling and sluggish proton-coupling electron transfers (PCET). Herein, CsPbBr₃ (CPB) quantum dots are in-situ encapsulated within amino-functionalized Fe/UiO-67-X (X = meta-NH₂, ortho-NH₂, ortho-2NH₂) frameworks for efficient CO₂ photoreduction. X-ray absorption spectroscopy confirms the presence of charge-asymmetrical ZrFe sites that promote C-C coupling and the covalently-connected Pb-N electron-transfer "bridge" that enhances carrier kinetics. Notably, the o-2NH₂-functionalized CPB@Fe/UiO-67-o-2NH₂ achieves a CH₃COOH productivity of 257.22 µmol·g^-1·h^-1 with 98.72% selectivity, whereas the m-NH₂-substituted analog (CPB@Fe/UiO-67-m-NH₂) exclusively produces HCOOH. Comprehensive analyses demonstrate that the o-NH₂ groups facilitate ultrafast electron transfer via a near Pb-N bridge and organize interfacial H₂O into proton-conducting networks to ensure synchronized proton-supply. In-situ DRIFT and DFT calculations confirm that the o-NH₂-induced rapid PCETdrives the conversion of ^*COOH at Zr sites to ^*CO, which subsequently couples with stabilized ^*COOH at Fe sites to form the critical ^*OC-COOH with the lowest energy barrier compared to ^*HOOC-COOH or ^*OC-CO pathways. This work establishes a design paradigm that necessitates the "temporal alignment" and "spatial coupling" of H⁺ and e^- at active sites for achieving high-performance CO₂-to-C2 photoreduction by modulating interfacial electron-proton dynamics through simple group isomerism.