Electrosynthesis of Ethylene Glycol from Methanol via Oxidative C-C Coupling.

Ethylene glycol (EG) is a commodity chemical, but its industrial production heavily relies on fossil-based feedstocks (that are, oil-based ethylene and coal-based syngas) and faces high carbon footprint. Herein, we report one-step electrosynthesis of EG from an important C1 platform molecule─methanol (MeOH), via oxidative C-C coupling at the anode. Over a boron-doped diamond (BDD) electrode, EG was produced with a Faradaic efficiency of 34.3% and a selectivity of 48.7% at a current density of 100 mA cm-2, delivering a productivity of 639 μmol cm-2 h-1. Mechanistic studies revealed that the reaction proceeded via a radical-mediated pathway, wherein H2O was first oxidized to the hydroxyl radical (•OH) on the BDD electrode, which mediated C-H bond activation of MeOH to deliver the •CH2OH intermediate, following C-C coupling to generate EG. To enhance EG selectivity, a paired-electrolysis strategy was designed that couples MeOH-to-EG at the anode and reduction of the byproduct formaldehyde to MeOH at the cathode. In a membrane-free flow cell, EG selectivity was increased from 48.7% to 72.1% with cycling stability over 80 h. This work demonstrates the opportunity to synthesize carbon-chain-propagated chemicals from basic C1 feedstock via radical-type C-C coupling by electrocatalysis.