Unraveling the Reaction Mechanism of Ethylene Glycol Electrooxidation on Palladium–Bismuth Catalysts

Abstract In alkaline electrolytes, electrochemical oxidation of ethylene glycol (EG) offers a renewable route to both energy generation and plastic-waste valorization. Palladium–bismuth (PdBi) was electrodeposited on two supports, nickel foam (NF) and carbon cloth (CC), for the study of EG oxidation mechanisms. Bismuth acts as a promoter rather than an active catalyst: it raises the activity of Pd and shifts the oxidation selectivity towards target products. Substrate choice mattered as well: PdBi@NF benefited from the underlying nickel's intrinsic activity but suffered from the oxygen-evolution side reaction tied to NiOOH formation, while PdBi@CC kept a cleaner surface and gave stable, reproducible selectivity. XRD and SEM characterizations confirmed alloy formation and a uniform, snowflake-like morphology, and XPS showed electron transfer from Bi to Pd, consistent with Bi's promotional role. In situ Raman spectroscopy showed substantially more Pd-OHads on PdBi@CC than on pure Pd@CC, pointing to a synergistic electronic effect. DFT calculations further support this finding: Bi lowers the Pd d-band center, destabilizes adsorbed intermediates, and favors surface hydroxyl formation relative to unmodified Pd. Selectivity depended strongly on potential. Below 1 V vs RHE, glycolic acid (GA) formed exclusively; above that, formic acid (FA) increasingly took over, a shift rationalized computationally through C─C bond cleavage energetics. Additional oxidation experiments on the individual EG-derived intermediates / products mapped out the full reaction network. Together these results show how Bi reshapes the EG oxidation pathway to limit overoxidation, pointing to rational design strategies for electrocatalysts relevant to both fuel cells and chemical upcycling.