A Cu Single-Atom Catalyst as an Intrinsic Hydrogen Atom Transfer Mediator for Electrooxidation of C(sp3)–H Bonds

Abstract

Electrochemical activation of C(sp3)–H bonds is an attractive and sustainable strategy for the synthesis of oxygenated chemicals, yet existing methods often suffer from high overpotentials and reliance on external hydrogen atom transfer (HAT) reagents. Here we report a Cu single-atom catalyst (Cu1/NC) that functions as both an electrocatalyst and an intrinsic HAT mediator, thereby establishing a catalyst-embedded HAT paradigm that eliminates the need for external HAT reagents. Under applied potential, Cu–N4 sites dynamically generate reactive Cu–O species in situ, which selectively abstract hydrogen atoms from hydrocarbons, thereby lowering the activation barrier and enhancing reaction selectivity. The system shows excellent catalytic performance across a wide substrate scope, achieving a Faradaic efficiency (FE) of 57.2%. Mechanistic studies combining isotopic labeling, radical trapping, electron paramagnetic resonance, in situ ATR-SEIRAS spectra, in situ Raman spectroscopy, and density functional theory calculations identify Cu–OH species as the key HAT-active intermediate and reveal that water-assisted deprotonation governs the rate-determining step. Notably, this catalyst exhibits both excellent stability and broad applicability. It enables continuous electrooxidation in a flow reactor at a current density of 50 mA·cm–2, achieving a turnover frequency (TOF) as high as 713 h–1. This work establishes a catalyst-embedded HAT paradigm for electrochemical C–H activation and provides a general framework for sustainable and selective oxidation of hydrocarbons.