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.

The electrocatalytic urea oxidation reaction (UOR) enables energy-saving hydrogen production and waste degradation but requires efficient catalysts due to its complex, sluggish 6-electron transfer mechanism. In this study, we designed a series of stable 3d transition metal heterometal atom pairs (TMNi, TM refers to Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn) supported on the C₂N substrate as UOR catalysts, systematically investigating their potential to enhance the activity of Ni₂/C₂N. Among these, CrNi/C₂N displayed a superior capability to lower the limiting potential of the UOR compared to CuNi/C₂N and Ni/C₂N. The enhanced catalytic CrNi/C₂N system primarily stems from the stronger TM–Ni interactions, notable differences in charge distribution, more localized electronic states, and a higher d-band center associated with CrNi/C₂N relative to CuNi/C₂N and Ni₂/C₂N. These attributes not only ensure the stability of the well-dispersed CrNi pairs on C₂N but also amplify the ability of the active center to adsorb and activate reaction intermediates. Moreover, CrNi/C₂N demonstrates good selectivity for the UOR by exhibiting reduced susceptibility to forming NO₂ by-products and undergoing the competing oxygen evolution reaction. This theoretically driven work identifies CrNi/C₂N as the top-performing UOR dual-metal-atom catalysts, combining 0.99 V limiting potential with selective N₂ generation through electronic structure modulation, offering guidance for advanced catalyst design through the strategic use of transition metal heterometal atom pairs.