Interfacial Electronic Interactions within the Pd-CeO₂/Carbon Onions Define the Efficient Electrocatalytic Ethanol Oxidation Reaction in Alkaline Electrolytes

Abstract

Porous Pd-based electrocatalysts are promising materials for alkaline direct ethanol fuel cells (ADEFCs) and ethanol sensors in the development of renewable energy and point-of-contact ethanol sensor test kits for drunk drivers. However, experimental and theoretical investigations of the interfacial interaction among Pd nanocrystals on supports (i.e., carbon black (CB), onion-like carbon (OLC), and CeO₂/OLC) toward ADEFC and ethanol sensors are not yet reported. This is based on the preparation of Pd-CeO₂/OLC nanocrystals by the sol-gel and impregnation methods. Evidently, the porous Pd-CeO₂/OLC significantly increased membrane-free micro-3D-printed ADEFC performance with a high peak power density (<i>P</i>_max = 27.15 mW cm^-2) that is 1.38- and 7.58-times those of Pd/OLC (19.72 mW cm^-2) and Pd/CB (3.59 mW cm^-2), besides its excellent stability for 48 h. This is due to the excellent interfacial interaction among Pd, CeO₂, and OLC, evidenced by density functional theory (DFT) simulations that showed a modulated Pd d-band center and facile active oxygenated species formation by the CeO₂ needed for ethanol fuel cells. Similarly, Pd-CeO₂/OLC gives excellent sensitivity (0.00024 mA mM^-1) and limit of detection (LoD = 8.7 mM) for ethanol sensing and satisfactory recoveries (89-108%) in commercial alcoholic beverages (i.e., human serum, Amstel beer, and Nederberg Wine). This study shows the excellent possibility of utilizing Pd-CeO₂/OLC for future applications in fuel cells and alcohol sensors.