Tracking and Tuning the C ₁ /C ₂ Pathway: In Situ Spectroscopy and Mechanistic Insights Into Ethylene Glycol Oxidation on Metal‐Based Catalysts

The electrocatalytic ethylene glycol oxidation reaction (EGOR), using ethylene glycol (EG) obtained from hydrolyzed polyethylene terephthalate (PET) waste, offers a route for converting this plastic into valuable chemicals. However, steering selectivity between the C ₁ and C ₂ pathways remains challenging. This Review focuses on in situ spectroscopy for tracking interfacial reaction dynamics under operating conditions. We summarize how in situ Raman and Fourier transform infrared spectroscopy enable real‐time identification of adsorbed intermediates and active species, providing mechanistic insights inaccessible to ex situ methods. We then evaluate noble‐metal and non‐noble‐metal catalysts and discuss how their structural characteristics regulate EG adsorption, OH ⁻ activation, and intermediate conversion. Particular attention is given to tuning C ₁ /C ₂ branching to improve activity, selectivity, and poisoning resistance. We further survey EGOR applications in electrolysis systems, including pairing with hydrogen evolution for coproduction of value‐added chemicals and hydrogen and coupling with CO ₂ reduction or organic synthesis to construct energy‐efficient electrochemical cells. Ultimately, such mechanistic understanding offers guidance for rational catalyst design and sustainable PET upcycling.