Journal of Electroanalytical Chemistry 944 (2023) 117673 Available online 18 July 2023 1572-6657/© 2023 Elsevier B.V. All rights reserved. Palladium-copper bimetallic surfaces as electrocatalysts for the ethanol oxidation in an alkaline medium M.D. Obradovi´ c a , U. ˇ C. Laˇ cnjevac b , V.V. Radmilovi´ c c , A. Gavrilovi´ c-Wohlmuther d , J. Kovaˇ c e , J.R. Rogan c , V.R. Radmilovi´ c f , S.Lj. Gojkovi´ c c, * a University of Belgrade  Institute of Chemistry, Technology and Metallurgy, Njegoˇ seva 12, 11000 Belgrade, Serbia b University of Belgrade  Institute for Multidisciplinary Research, Kneza Vi ˇ seslava 1, 11030 Belgrade, Serbia c University of Belgrade  Faculty of Technology and Metallurgy, Karnegijeva 4, 11120 Belgrade, Serbia d Schoeller-Bleckmann Nitec GmbH, 2630 Ternitz, Austria e Joˇ zef Stefan Institute, Department of Surface Engineering, Jamova 39, SI-1000 Ljubljana, Slovenia f Serbian Academy of Sciences and Arts, Knez Mihailova 35, 11000 Belgrade, Serbia A R T I C L E INFO Keywords: Ethanol oxidation Palladium Copper Electrochemically active surface area Fuel cell ABSTRACT Two types of Cu-modifed Pd catalysts supported on high area carbon were prepared: Pd nanoparticles modifed with a sub-monolayer of underpotentially deposited Cu (Cu@Pd/C) and Pd-Cu alloy nanoparticles (Pd-Cu/C), and examined for the ethanol oxidation reaction (EOR) in alkaline solution. The catalysts were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy and X-ray photoelec- tron spectroscopy, as well as cyclic voltammetry. As reference catalysts, Pd/C and Pt/C were used. The elec- trochemically active surface area of all samples was determined from CO ads and Cu upd desorption and Pd oxide reduction, and used to assess their intrinsic activity for EOR. Intimate contact of Pd with Cu atoms enhanced its activity, regardless of the type of bimetal catalyst. The atomic Pd:Cu ratio between 2:1 and 4:1 appears to be optimal for high activity. The most active catalyst under the potentiodynamic conditions was Cu@Pd/C with θ(Cu) = 0.21,although Pd-Cu/C was superior during the potentiostatic test. All bimetallic catalysts surpassed Pd/C in mass activity. The EOR activity of Pt/C was higher compared to Pd-based catalysts at low potentials, both in terms of specifc and mass activity, but with a signifcant decline over a 30-min potentiostatic stability test. 1. Introduction The necessity of replacing traditional energy sources with renewable and green alternatives has initiated vast research of direct alcohol fuel cells (DAFC) with methanol and ethanol as the most common choices as fuel. Owing to the recent development of anion exchange polymer membranes, alkaline media come into focus due to the more facile ki- netics of alcohol oxidation and greater choice of electrocatalytic mate- rials compared to acidic media. Although the mechanism of methanol oxidation is less complex, when compared to the ethanol oxidation re- action (EOR), numerous other characteristics of ethanol make it more suitable for general applications. Ethanol is non-toxic and its crossover through a membrane is lower than that of methanol due to larger molecule size. It is also a renewable energy source because it can be produced by fermentation of sugar-containing biomass. The theoretical mass energy density of ethanol is higher than that of methanol (8.0 vs 6.1 kWh kg 1 ), with the assumption that 12 electrons are exchanged per ethanol molecule and 6 electrons per methanol molecule. However, the splitting of C – C bond in ethanol is energetically diffcult and great ef- forts are still required in electrocatalysts development in order to fully exploit the high mass energy density of ethanol [1,2]. Electrochemical oxidation of alcohols in either acidic or alkaline media requires a noble metal, Pt or Pd, to adsorb the molecule, but also some other oxophilic metal to facilitate further reaction of the adsorbed intermediates. Their promoted oxidative desorption can be achieved by introducing oxygen-containing species at the surface, which may also modify the electronic structure of the noble metal centers and thus weaken the strong adsorbate–noble metal bond. Both Pt and Pd are active in alkaline media for the EOR. According to various research groups, their activities are the same [3], Pd is more active than Pt * Corresponding author. E-mail address: sgojkovic@tmf.bg.ac.rs (S.Lj. Gojkovi´ c). Contents lists available at ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem https://doi.org/10.1016/j.jelechem.2023.117673 Received 16 May 2023; Received in revised form 27 June 2023; Accepted 17 July 2023