## 1 Introduction  
Direct alcohol fuel cells (DAFCs) have been considered as an alternative source of energy for many electronic devices [1, 2]. DAFCs present several advantages over lithium-ion batteries (LIBs), which are normally used in these electronic devices, and hydrogen-feed polymer electrolyte membrane fuel cells (PEMFCs). LIBs cannot be used as the power source in portable devices or even in stationary devices where an electrical energy source is not available. Under these conditions, DAFCs are the best choice for such devices [3, 4]. Although the theoretical voltage of DAFCs and PEMFCs are approximately the same, alcohols present with fewer problems of storage and transportation. Alcohols have a high energy density (4000-7000 Wh L [1]) which is similar to those of hydrocarbons (9800 Wh L [5]) while the power density of hydrogen (180 Wh L [1]) is lower than DAFCs [5]. These properties reflect the theoretical superiority of DAFCs over PEMFCs. Different kinds of alcohols can be used as fuel in DAFCs, each of them has its own advantages and disadvantages [6]. Although there are studies on the use of ethylene glycol [7], propanol [8], and butanol [9] as fuels in DAFCs, the most widespread alcohol-based fuels are methanol and ethanol [10, 11, 12, 13, 14, 15]. In addition to the high energy density and nontoxicity of ethanol, the balance of CO\({}_{2}\), the most common greenhouse gas, in the environment is preserved during ethanol oxidation because ethanol can be obtained from biomass. Thus, there is a circulation between ethanol consumption and ethanol production through the fermentation process of agricultural products [6]. Regarding its oxidation mechanism on platinum electrodes, it has been well confirmed that ethanol oxidation reaction (EOR) can take place through a parallel pathway [16; 17; 18]. In the first route (blue arrows in Figure 1), the so-called C2 pathway, the C-C bond is not broken, and ethanol is first oxidized to acetaldehyde, which can be further oxidized to acetic acid (or acetate in alkaline solution) [19; 20]. This route exchanges four electrons and releases only one-third of the formal energy density of ethanol. The release of the whole energy stored in ethanol is obtained through the C1 pathway with the exchange of twelve electrons. This route (green arrows in Figure 1) proceeds through the breaking of the C-C bond in the early stages of the oxidation process and produces adsorbed CO which can be further oxidized to CO\({}_{2}\) (or carbonate in alkaline solution). CO is considered a poison intermediate because it is strongly adsorbed on the surface (blocking surface sites) and its oxidation requires high overpotentials. The efforts that expedite oxidation of CO to CO\({}_{2}\) and decrease the potential of CO oxidation remarkably improve the electrocatalytic activity towards EOR [20]. Nowadays, the oxidation of alcohols, like ethanol, in alkaline media has gained attention since non-Pt-based catalysts, such as Pd-based catalysts, can be used as the electrocatalyst for the oxidation and reduction reaction [21]. These alternative catalysts may decrease the cost of DEFCs and facilitate their commercialization [22; 23]. The prevailing mechanism of the EOR produces acetaldehyde through the cleavage of the C-H bond, which can undergo the aldol condensation reaction in alkaline media. When the aldol condensation reaction is faster than acetaldehyde oxidation to produce acetate the catalyst surface with \(\beta\)-hydroxy aldehyde. Since the electrocatalytic activity of materials is connected to their composition and morphology, replacement of Pt with other elements such as Pd not only mitigates the catalyst poisoning but may also decrease the cost. Mono and bimetallic Pt and Pd nanoparticles have been used for the electrocatalytic oxidation of ethanol. In all these studies, PtPd nanoparticles on different supports show better electro-catalytic properties than pure Pt or Pd nanoparticles [23; 24; 25; 26; 27; 28; 29; 30; 31; 32].