EIS-Activity Correlation for the Electro-Oxidation of Ethylene Glycol at Nanoparticles-Based Electrocatalysts

• Published in: Journal of the Electrochemical Society 2019, Vol.166 (6), p.F364-F376
• Main Authors: El-Nowihy, Ghada H., Mohammad, Ahmad M., Sadek, Mohamed A., Khalil, Mostafa M. H., El-Deab, Mohamed S.
• Format: Article
• Language: English
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/2.0191906jes

Enhanced catalysis of ethylene glycol electro-oxidation (EGO) is reported at a ternary CoOx/NiOx/Pt catalyst in which Pt nanoparticles (nano-Pt), nickel oxide nanoflowers (nanoNiOx), and cobalt oxide nanoparticles (nano-CoOx); are respectively electrodeposited onto a glassy carbon (GC) substrate. The electrocatalytic activity of the catalyst toward EGO depends on the catalyst's composition, loading sequence and loading level besides the electrolyte's pH and temperature. A detailed morphological, compositional, and structural inspection for the catalyst is achieved by FE-SEM, energy dispersive X-ray spectroscopy, and X-ray diffraction, respectively. Cyclic voltammetry is employed to ensure the successful electrodeposition of the catalyst's ingredients and to assess its activity. The superiority of the CoOx/NiOx/Pt/GC catalyst over a series of catalysts employing different ingredients and/or deposition sequence is demonstrated. It supports a larger (ca. fourfold) oxidation peak current, and a significant (ca. ‒330 mV) negative shift in the onset potential of EGO together with a much more enhanced long-term stability toward continuous electrolysis when compared to the Pt catalyst. The novelty of this investigation extends to employing the electrochemical impedance spectroscopy (EIS) as a probe that provides important information about the reaction pathway of EGO. Interestingly, the maximum capacitance obtained at the CoOx/NiOx/Pt/GC catalyst (coincides with the EGO peak current) is fivefold higher than that obtained at the Pt/GC catalyst at ‒0.35 V vs. Ag/AgCl. Formic acid and oxalic acid were the major products of EGO, as revealed by high performance liquid chromatography.