Resumo:
One of the main challenges in the preparation of gas diffusion electrodes is related with the cost of platinum that is the main component of the catalytic layer. In this context, palladium is an interesting candidate to substitute platinum, partially or completely, presenting a good catalytic activity on reactions using hydrogen. In this study, the electrodeposition of palladium was investigated by using electrochemical techniques assisted by ultrasound. The electrochemical deposition was studied by using a complete factorial design 24 as a chemometric tool, aiming to reduce the number of experiments and estimate the effects of interactions between the variables. The investigated variables were the number of deposition cycle (NDC = 100 and 300 cycles); scan rate (SR = 50 and 100 mV s -1 ); Pd2+ concentration ([Pd2+] = 0.5 and 1.0.10-3 mol L-1 ) and in the absence or presence of ultrasound waves (US, 100 W). The electrochemically active surface area (ECSA) was used as response. According with the study, all variables were significant, with the US being more significant. Some second and third order interactions were also significant. The best condition evaluated was that performed with higher NDC and [Pd²+ ], in lower SR and in the presence of ultrasound. Through the application of the ANOVA-PCA technique, it was possible to observe that all variables contribute to a change in the profile of the observed voltammetric responses, especially in the peak related to the hydrogen desorption process, with US being the variable that most contributed to this change. Morphological and structural analyses by scanning electron microscopy (SEM), Field Emission Gun Scanning Electron Microscopy (FEG), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) were performed. XRD analyses indicated the presence of Pd in a cubic phase, under conditions that provided the highest ECSA values. The EDS results indicated that the condition of 300 cycles, at 50 mV s-1 , 1.10-3 mol L-1 , in the presence of US presented the highest values of mass and atomic percentage for Pd, despising the impurities (22.14% and 2.50%, respectively). In this study, it was possible to verify the influence of the use of ultrasound during the Pd electrodeposition process, which promoted an increase in the amount of electrodeposited Pd, thus affecting the morphology of the Pd clusters and, as a consequence, a difference in the voltammetric profile and in the value of ECSA
