Elemental trade-off in the selective Electrooxidation of Ethylene Glycol on Palladium-Silver/Nickel Electrodes.

We study the synthesis and properties of PdAg electrodes coated on Ni foam and their application in the selective electro-oxidation of ethylene glycol to glycolate. This reaction is a route to glycolic acid, which is a key component of biodegradable packaging. Using a combination of cyclic voltammetry, EDX and XRD analysis, we find that a 3:1 Pd:Ag ratio gives optimal results. We show that the oxidation of ethylene glycol on palladium occurs between 0.3 and 1.2 V vs. RHE, and depends on the presence of a Pd(0) active site. Electrochemical Impedance Spectroscopy experiments show that the charge-transfer resistance (RCT) follows the same trend as EGOPd activity, with the 3:1 Pd:Ag electrode having the lowest RCT. Electrolysis with this electrode at 0.705 V vs. RHE, where Pd is reduced, results in glycolate production with no overoxidation to formate or oxalate. We then move to a flow setup under industrial conditions, and show that the Pd-Ni electrode yields >80% FE to glycolate for over 140 h. Long-term electrode deactivation can be overcome in this system by a periodic self-refresh cycle.