Electrochemical valorization of poly-(ethylene terephthalate) (PET) into glycolic acid (GA) mediated by ethylene glycol monomers offers a promising approach for upcycling waste plastic. However, this process faces significant challenges, including low selectivity arising from multiple proton-coupled electron transfer steps and limited reaction rates attributed to the sluggish kinetics as well as the insufficient diffusion of reactants. Herein, we report the construction of a robust PdCu nanocatalyst via electrochemical dealloying of a bimetallic PdCu₅ contained intermetallic PdCu₃ structure precursor. This catalyst features a Pd-skin with an intermetallic PdCu₃ core and a nanoporous structure featuring ∼ 2.4 nm in size. In-situ electrochemical ICP-MS and surface-enhanced IR spectroscopy reveal its structural stability and a predominant C2 pathway through the HOCH₂C*O intermediate toward GA electrosynthesis, respectively. A high mass activity of up to 9.95 A mg_Pd ^-1 and a Faradaic efficiency for GA exceeding 92% across a broad potential window have been achieved. Furthermore, by integrating this nanoporous PdCu catalyst into the anode of a membrane-free flow cell electrolyzer and optimizing the flow field, continuous and stable GA electrosynthesis at 200 mA cm^-2 using PET-derived ethylene glycol has been demonstrated for over 110 h, with the GA Faradaic efficiency ranging from 86.6% to 95.4% and a yield of 0.51 g_GA per gram of PET.