Energy-saving hydrogen production coupled with PET-derived ethylene glycol oxidation: Reaction mechanisms, catalyst design, and reactor engineering

The growing accumulation of poly(ethylene terephthalate) (PET) waste and the increasing demand for clean hydrogen call for integrated electrochemical strategies. Ethylene glycol oxidation reaction (EGOR), derived from PET hydrolysis, offers a thermodynamically favorable alternative to the sluggish oxygen evolution reaction (OER) and can be coupled with the hydrogen evolution reaction (HER) to simultaneously produce value-added chemicals and H₂. This review provides a system-level overview of EGORHER paired electrolysis, spanning reaction fundamentals, catalyst design, cell configuration, and future challenges. First, the competing EGOR pathways toward C1 products (such as formate/formic acid) and C2 products (such as glycolate/glycolic acid) are discussed. Key energetic descriptors, including cell voltage, overpotential, Faradaic efficiency, and energy efficiency, are then summarized to clarify the advantages of replacing OER with EGOR. Recent advances in catalysts, including precious metals, transition-metal compounds, metal–organic frameworks (MOFs), organic catalysts, and hybrid systems, are reviewed with attention to their bifunctional or compatible activity for EGOR and HER. Reactor design is further discussed by comparing single-cell and dual-cell H-type reactors with membrane-free and membrane-separated flow-cell reactors, emphasizing their different roles in mass transport, product separation, and scale-up feasibility. Finally, remaining challenges and future directions are proposed, including C1/C2 selectivity, downstream separation, impurity tolerance, catalyst durability, and practical reactor optimization. This review aims to guide the development of efficient EGOR-assisted hydrogen production systems for sustainable PET electro-upcycling.