PtSnIr/C anode electrocatalysts: promoting effect in direct ethanol fuel cells

Abstract

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...

Oxidation of ammonia using PtRh/C electrocatalysts: Fuel cell and electrochemical evaluation

“…The observed shift indicates a lattice constriction due to the incorporation of smaller Rh atoms into the Pt fcc structure, suggesting the alloy formation of Pt-Rh. In order to confirm the alloy formation, the 220 crystal planes were deconvoluted and the lattice parameters were calculated for all synthetized materials, as already reported on the literature [29,30].…”

Iridium Application in Low‐Temperature Acidic Fuel Cells: Pt‐Free Ir‐Based Catalysts or Second/Third Promoting Metal in Pt‐Based Catalysts?

“…[88][89][90][91][92][93][94][95][96][97] Excluding Pt-Ru-Ir [90] and Pt-Cu-Ir, [91] all papers focused on Pt-Sn-Ir catalysts, that is, on the addition of Ir to benchmark Pt-Sn. [88][89][90][91][92][93][94][95][96][97] Excluding Pt-Ru-Ir [90] and Pt-Cu-Ir, [91] all papers focused on Pt-Sn-Ir catalysts, that is, on the addition of Ir to benchmark Pt-Sn.…”

“…[88] Thus, formation of a Pt-Sn alloy is revealed by the increase of the lattice parameter, but the formation a ternary PtSnIr alloy as well as the presence of Sn and Ir oxides cannot be discarded. [92] DEFC tests at 90-110 8C with Pt-Sn-Ir/C as anode catalysts [88,93,94,96] showed that Ir presence enhances the EOR activity of Pt-Sn/C. Indeed, the binary Pt-Sn/C and ternary Pt-Sn-Ir/C catalysts give better results than the binary Pt-Ir/C and pure Pt/C.…”

“…[88][89][90][91][92][93][94][95][96][97] Excluding Pt-Ru-Ir [90] and Pt-Cu-Ir, [91] all papers focused on Pt-Sn-Ir catalysts, that is, on the addition of Ir to benchmark Pt-Sn. [88,89,[92][93][94][95][96][97] The addition of Ir to Pt leads to a decrease in the lattice parameter, in agreement with the Vegard's law for a true PtIr alloy. [88] On the other hand, an increase in Sn loading for both binary and ternary electrocatalysts leads to an increase in the lattice parameter up to a 25 at % Sn, suggesting that there is a straight dependence of the lattice parameter on Sn content, which also follows Vegard's law.…”

“…[88] Pt-Sn-Ir (75:20:5) presented higher activity for ethanol oxidation at 60 8C than Pt-Sn-Rh (77:15:8) and Pt-Sn (75:25). [92] DEFC tests at 90-110 8C with Pt-Sn-Ir/C as anode catalysts [88,93,94,96] showed that Ir presence enhances the EOR activity of Pt-Sn/C. MPD ratio can be observed at 25 Ir at % in Figure 7 a, followed by a slow decrease of the curve.…”