## 2 Experimental
### Electrochemical Experiments
#### 3.2.2 Ethanol Electrooxidation: Potentiodynamic Measurements  
The catalytic properties of Pt, Pt4 Pd, Pt3 Pd2, Pt2 Pd3, PtPd4, and Pd for the EOR were analyzed by voltammetry in a 0.1M NaOH solution containing 0.1 M ethanol, as shown in Figure 6. The analysis of the profiles aims to address these four issues: (1) the comparison between the intrinsic activity of Pt and Pd nanoparticles towards the EOR (2); the influence of the interfacial electronic structures of PtPd nanoparticles on EOR activity; (3) the trend of synthesized nanoparticles for the deactivation; and (4) the identification of the intermediate species which are responsible for the electrocataly poisoning and the current diminution upon cycling. The specific activities were calculated via the normalizing of the currents to the active surface area of the nanoparticles [46]. As it is seen in Figure 6, the peaks attributed to H ab(d)sorption/desorption are suppressed and two well-defined anodic peaks appear in the forward and backward scans. The disappearance of the hydrogen peaks is attributed to the adsorption of the resultant ethoxy species, such as (CH3 CO)ads, which blocks the electroactive sites. The activity for the positive scan direction reaches a maximum at ca. 0.8 V and then decrease as potential increases. The downfall of the current density corresponds to the formation of the Pd and Pt oxide layers, which block the adsorption of the reactive species onto the catalyst surface and lead to a decrease in the electrocatalytic activity. At 1.2 V, the surface of the nanoparticles is completely covered with PdO or PtO, which is inactive for the EOR, and the current density at this potential coincides with that recorded in absence of ethanol. When the scan is reversed and PdO or PtO is reduced, the electrode recovers its activity. This phenomenon results in the appearance of a peak in the negative scan direction [20,29]. There is a hysteresis between the positive and negative scan directions. First, the peak intensity is lower in the negative scan direction. This diminution can be due to two different reasons: (i), the surface in the negative scan direction is still partially covered by PtO or PdO and/or (ii) the surface has been poisoned by the polymerization of the acetaldehyde (which is the result of the partial oxidation of  
Figure 5: Voltammetric profile of the modified glassy carbon electrode (GCE) with (**a**) Pt, (**b**) Pt4 Pd, (**c**) Pt3 Pd2, (**d**) Pt2 Pd3, (**e**) PtPd4, and (**f**) Pd nanoparticles in 0.1 M NaOH solution at the scan rate of 0.05 V s \({}^{1}\). ethanol) through the aldol condensation. On the other hand, at ca. 0.5 V, which is the onset of the EOR, currents in the negative scan direction are higher, which reveals that in the positive scan direction the surface may be blocked by some ethoxy adsorbed species, which have been oxidized at higher potentials. Regarding the evolution of the current densities with the PtPd ratio (Figure 6), PtPd binary catalysts exhibit considerable improvements over pure Pt and Pd [22; 53 acetaldehyde [19; 20; 54; 55], a lower deactivation rate indicates a higher efficiency in the oxidation of acetaldehyde to acetate. This fact implies that Pt is more active in the first step in the formation of acetaldehyde, but the oxidation of acetaldehyde to acetate seems to be more facile on Pd. The further oxidation of acetaldehyde to acetate requires the transfer of an oxygen group. As shown in Figure 5, Pd oxide is formed at a lower potential than the Pt oxide. Since the previous step in the surface oxidation is the adsorption of OH, OH adsorption on Pd should take place also at a lower potential, probably just after the desorption of hydrogen. Thus, the higher amount of adsorbed OH on the surface facilitates the second step. The increase of the electrocatalytic activity and poison resistance with the incorporation of Pd on the Pt nanoparticles should be then connected to a bifunctional effect.