Este estudo investiga o efeito promotor de anodos eletrocatalisadores do tipo PtSnIr/C (1:1:1), preparados pelo método de precursor polimérico, na reação de oxidação de etanol em uma célula a combustível de etanol direto (DEFC). Todos os materiais usados foram metal 20% m/m com relação a carbono. Análise por espectroscopia fotoelétrica de raios X (XPS) mostrou a presença de Pt, PtOH 2 , PtO 2 , SnO 2 e IrO 2 na superfície do eletrocalisador, indicando uma possível estrutura de partícula revestida. Análise por difratometria de raios X (XRD) indicou Pt e Ir metálicos assim como a formação de uma liga com Sn. Utilizando eletrocatalisadores do tipo PtSnIr/C preparados para este estudo com quantidades de Pt duas vezes menor que em eletrocatalisadores do tipo PtSn/C E-tek, foi possível obter a mesma densidade de potência máxima encontrada para o material comercial. O produto de reação principal foi ácido acético provavelmente devido a presença de óxidos, neste caso o mecanismo bifuncional é predominante, mas um efeito eletrônico não deve ser descartado.This study investigates the promoting effect of PtSnIr/C (1:1:1) electrocatalyst anode, prepared by polymeric precursor method, on the ethanol oxidation reaction in a direct ethanol fuel cell (DEFC). All of the materials used were 20% metal m/m on carbon. X-ray photoelectron spectroscopy (XPS) analysis showed the presence of Pt, PtOH 2 , PtO 2 , SnO 2 and IrO 2 at the electrocatalyst surface, indicating a possible decorated particle structure. X-ray diffractometry (XRD) analysis indicated metallic Pt and Ir as well as the formation of an alloy with Sn. Using the PtSnIr/C electrocatalyst prepared here with two times lower loading of Pt than PtSn/C E-tek electrocatalyst, it was possible to obtain the same maximum power density found for the commercial material. The main reaction product was acetic acid probably due to the presence of oxides, in this point the bifunctional mechanism is predominant, but an electronic effect should not be discarded.Keywords: PtSnIr , ethanol oxidation reaction, electrocatalysis, nanostructured materials, fuel cells IntroductionPolymeric exchange membrane fuel cells (PEMFCs) have been extensively studied due to their mobile, stationary and portable applications.1,2 Among the PEMFCs, direct alcohol fuel cells (DAFCs) have the advantage that the liquid fuel can be more easily stored and handled compared to hydrogen. 3Ethanol is a more attractive fuel alcohol for PEMFC applications when compared with methanol because it is much less toxic, can be produced at a large scale from agricultural products or biomass, 4,5 and is more energetic (8 kWh kg −1 vs. 6.1 kWh kg −1 ). 6 For these reasons, direct ethanol fuel cells (DEFCs) should achieve similar performance levels as direct methanol fuel cells.However, the complete electrooxidation of ethanol is a 12-electron process, which is a practical challenge for the effectiveness of the catalysts. Pt is the most used metal for Silva et al. 1147 Vol. 23, No. 6, 2012 the oxidation of this alcohol, and it...
In this work were used Sn and Ni as second metals with Pt to study both the electrochemical oxidation of ethanol using "in situ" ATR-FTIR and the oxygen reduction reaction which is assessed using a rotating ring disk electrode technique (RRDE). The onset potential of ethanol oxidation is 0.3 V for PtSn/C, and 0.4 V for PtNi/C. Acetic acid is the main product formed using PtSn/C while using PtNi/C CO2 is the main product. The current densities for ORR using PtSn/C were similar to those ones using PtNi/C in all potential regions, including the region of limit diffusion current. However, the peroxide production was smaller for PtNi/C than PtSn/C between -0.1 to -0.5 V. For PtNi/C, the reaction proceeds through the transfer of 3.7 electrons, while for PtSn/C about 3.8 electrons.
This paper presents a study involving the use of Pt 3 Sn/C electrocatalysts as cathodes and anodes in a single direct ethanol fuel cell. First, we studied the oxygen reduction reaction (ORR) using commercial Pt/C from ETEK and Pt 3 Sn/C as electrocatalysts with an alloy degree of 92 %. The electrocatalytic activity of the material for oxygen reduction was assessed using the rotating disk electrode technique (RDE). When Pt 3 Sn was tested for ORR in the presence of ethanol, the results showed greater tolerance to the cross-over effect than Pt/C in the electrochemical cell. The experiments in a single direct ethanol fuel cell showed that without oxygen pressurization of the cell, the maximum power density is higher using Pt 3 Sn/C as both cathode and anode than using Pt 3 Sn as an anode and Pt/C as a cathode. When using Pt 3 Sn/C as both the cathode and anode in a direct ethanol fuel cell, cell performance enhances.
In the present work, we investigated PtSnCe/C (68:22:10), PtSnIr/C (33:33:33) and commercial PtSn/C (E-Tek) electrocatalysts as anodes in a DEFC. The effects of decreasing the Pt content in the electrocatalysts were also investigated. The product distributions resulting from the ethanol oxidation reaction (EOR) in acid solutions using PtSnCe/C, PtSnIr/C and the commercial PtSn/C materials as electrocatalysts were determined by in situ FTIR spectroscopy. All of the anodes contained 20% (w/w) metal on carbon. From in situ FTIR experiments using 2.0 mol L-1 ethanol, it was observed that the PtSnCe/C and PtSnIr/C materials led to the formation of acetic acid as the predominant oxidation product. The best results for the EOR were obtained with the PtSnCe/C material. However, it was observed that the PtSnIr/C electrocatalyst material tolerated a decrease in Pt content while still showing good performance.
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