Elucidating In Situ Impedance Kinetic Mechanisms for Selective Ethylene Glycol Electrooxidation to Formate Production Regulated by Mo-Doped NiCo 2 O 4

Replacing the sluggish anodic oxygen evolution reaction (OER) with the value-added ethylene glycol oxidation reaction (EGOR) is a promising strategy for energy-efficient hydrogen production. However, achieving high Faradaic efficiency (FE) and selectivity, while elucidating the complex reaction kinetics and mass transport mechanisms coupled with the hydrogen evolution reaction (HER), remains challenging. Herein, a Mo-doped NiCo 2 O 4 electrocatalyst, synthesized via a CTAB-assisted method, achieves >98% FE and >98% selectivity for ethylene glycol (EG) electrooxidation to formic acid (FA) at 100 mA/cm 2 in a three-electrode half-cell configuration. Density functional theory (DFT) reveals that Mo doping optimizes the electronic structure, thereby lowering the rate-determining step (RDS) energy barrier for selective FA production. An asymmetric flow field anion exchange membrane (AEM) flow electrolyzer was designed to overcome mass transport limitations, enabling a 143 mV reduction in cell voltage compared to conventional water electrolysis and stable operation over 30 h. In situ electrochemical impedance spectroscopy (EIS) with the distribution of relaxation times (DRT) quantitatively decouples ion transport, charge transfer, and mass transfer resistances under operational conditions. Systematic optimization of current density, flow rate, and EG concentration demonstrated synergistic regulation of kinetics and mass transport. This work provides a high-performance system for the co-production of green hydrogen and valuable chemicals and establishes a universal diagnostic framework for optimizing hybrid electrolysis systems.