Desenvolvimento de catalisadores de Pd modificados por Ag, Ru e Mo para atuar como ânodo em células a combustível de etanol direto em meio alcalino
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Data
2022-03-14
Autores
Filho, Yonis Fornazier
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Universidade Federal do Espírito Santo
Resumo
Pd catalysts modified by Ag, Ru and Mo were produced by the thermal decomposition of polymeric percussor method to study their catalytic properties to ethanol oxidation reaction (EOR) in alkaline medium for fuel cells. Vulcan XC72 carbon was used as support, and the catalysts Pd/C, Pd60Ru40/C, Pd70Ru20Mo10/C, Pd60Ru20Mo20/C, Pd80Ag20/C, and Pd60Ag40/C were synthesized. Good experimental yields (Pd/C, Pd60Ru40/C, Pd70Ru20Mo10/C, Pd60Ru20Mo20/C, Pd80Ag20/C e Pd60Ru40/C = 97.1, 90.2, 97.9, 98.0, 98.6 e 96.5% respectively) and an increase in superficial area with addition of the metals were archieved (Pd/C, Pd60Ru40/C, Pd70Ru20Mo10/C, Pd60Ru20Mo20/C, Pd80Ag20/C e Pd60Ru40/C = 27.5, 100, 47.2, 38.9, 84.8 e 103.6 m2/g respectively). The X-ray diffraction and Raman spectroscopy results, showed formation of PdO for the Pd/C catalyst and RuO2 for the Pd60Ru40/C catalyst, a fact not observed for the other catalysts. Diffraction peak shifts were also observed for Pd70Ru20Mo10/C, Pd60Ru20Mo20/C, Pd80Ag20/C and Pd60Ag40/C, suggesting the formation of alloys in these catalysts. The electrochemical activities were investigated in alkaline medium, and an increase in the electrically active area was observed when the metals were combined with Pd and with the Ag-modified catalysts having the highest values (Pd/C, Pd60Ru40/C, Pd70Ru20Mo10/C, Pd60Ru20Mo20/C, Pd80Ag20/C e Pd60Ru40/C = 2.36, 4.63, 4.24, 3.04, 7.62 e 11.5 m2/g respectively). In the cyclic voltammetry tests for EOR in alkaline medium, the catalysts Pd70Ru20Mo10/C, and Pd60Ru20Mo20/C showed more negative onset potentials (-0.69 e -0.68 V respectively), suggesting that the initiation of the reaction was facilitated in these catalysts and the catalysts Pd80Ag20/C and Pd60Ag40/C had higher current densities at the oxidation peak (44.7 e 64.8 mA cm-2 respectively). In the chronoamperometry tests it was observed that the Pd60Ru40/C catalyst showed the lowest susceptibility to poisoning due to the bifunctional mechanism promoted by the presence of RuO2, followed by the PdAg/C catalysts, due to the electronic effect mechanism (intrinsic mechanism). From the CO-Stripping voltammetry results, in which the Pd60Ag40/C and Pd60Ru20Mo20/C catalysts showed a higher ability to remove CO intermediates from Pd active sites in EOR and stability tests, in which the catalyst Pd60Ag40/C had the highest values of current density after approximately 600 minutes of reaction (132 mA cm-2) and also because these catalysts have shown greater savings in the amount (Pd60Ag40/C ~ 36.65% e Pd60Ru20Mo20/C ~ 64.1 %) of Pd (a noble and expensive metal), it is concluded that these catalysts can be considered the most viable for commercial applications as anode in EOR in alkaline medium, being suggested more tests to investigate their properties.
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Eletrocatálise , Células a combustível , Reação de oxidação do etanol , Paládio , Performance com economia