The dual role of the surface oxophilicity in the electro-oxidation of ethanol on nanostructured Pd/C in alkaline media

Abstract

• Pd/C electrocatalysts are used for amperometric sensors and also for Fuel Cells. • Size-induced effects on Pd/C resulted in distinct tendency to interact with oxygen. • Electrocatalytic activity towards ethanol oxidation depends on the surface oxophilicity. • PdO acts both as a promoter and/or inhibitor towards ethanol oxidation. • The catalytic activity can be enhanced by 57% only by varying surface oxophilicity. The ability of a surface to interact with oxygen (oxophilicity) plays a very important role in several catalytic, electroanalytic and electrocatalytic reactions. To date, however, the role of the oxophilicity in the electrochemical oxidation of ethanol was never shown for pure nanostructured Pd electrocatalysts supported on carbon, a promising material to be used as a non-enzymatic amperometric sensors for ethanol and also as an electrocatalyst for the Direct Ethanol Fuel Cells. In this work, Pd nanoparticles were prepared by chemical reduction at room temperature in the presence of varying amounts of sodium citrate in order to produce particles with distinct sizes. Then, we used cyclic voltammetry in 0.1 mol L -1 KOH to obtain an oxophilicity trend among various nanostructured Pd/C samples. The oxidation of ethanol in alkaline media demonstrated that the surface oxophilicity has a dual role in the kinetics of the reaction: a promoter at low and medium oxygen coverages, and a spectator (inhibitor) species at high surface coverages. Thus, by a proper control of the surface oxophilicity the current density at a constant potential can be enhanced by 57%, highlighting the importance of that parameter in the electro-oxidation on ethanol on Pd-based materials. Our results have a great impact for the design of more active non-enzymatic ethanol sensors and also for the development of more active electrocatalysts for Direct Ethanol Fuel Cells.