Electrooxidation of Mixed Ethanol and Methanol Solutions on PtSn/C Electrocatalysts Prepared by the Polymeric Precursor Method

Abstract

Different mass ratio proportions of PtSn (m/m) electrocatalysts with 20% metal loading on a carbon support were prepared for use in ethanol:methanol solutions oxidation reactions. PtSn/C (3:1) (91% alloy degree, lattice parameter of 0.399 nm and mean crystallite size 4.8 nm) presented the best activity for oxidation of mixed solutions. The highest normalized current (ethanol:methanol 80:20) was 4.2 mA mg Pt -1 (measured after 1800 seconds at 0.5 V). Therefore, the PtSn/C (3:1) electrocatalyst with an atomic ratio of 65:35 enhanced both the electronic effect and bifunctional mechanism in (ethanol:methanol 80:20), which resulted in the formation of CO 2 at low potentials, as well as the highest amount of by-products than ethanol and methanol. Keywords: electrooxidation, PtSn/C, electrocatalysts, FTIR-ATR in situ, ethanol:methanol solutions IntroductionThe evolution of technology makes the search for new energy sources necessary, preferably using renewable alternative fuels.1,2 The use of PEMFCs (proton exchange membrane fuel cells) that turn chemical energy into electrical energy has been widely studied as an alternative due to its high efficiency and low greenhouse gases emission. [3][4][5] However, PEMFCs have a high cost due to the use of a Pt electrocatalyst and difficulties related to the transport and storage of hydrogen. [6][7][8][9] Therefore, other fuel options, such as methanol and ethanol, [10][11][12][13][14][15] have been studied because they are liquids and have a relatively high energy density. 16 For the methanol oxidation reaction, formaldehyde, formic acid, CO and CO 2 are produced, and methanol is the least reactive among these molecules in production of CO 2 .17 Therefore, the rate-determining step in methanol oxidation to CO 2 is associated with the conversion of methanol to formaldehyde (i.e., oxidation of the first two electrons). In addition, the slow kinetics of methanol as well as its crossover and toxicity are problematic. 18Ethanol can be obtained from biomass and has a higher energy density (8.0 kW h kg -1 ) compared to that of methanol (6.1 kW h kg -1 ), 19,20 but the oxidation of ethanol may involve a complex reaction pathway, and may be produced CO, acetaldehyde, acetic acid, CO 2 as well as 2-carbon intermediates. 21,22 Therefore, a mixture of ethanol and methanol can provide new reaction pathways, which may favor the formation of different intermediates and contribute to more effective electron transfer than that during oxidation in pure solutions. These pathways may improve the electrocatalytic activity. Therefore, investigation of the oxidation reactions of different ratios of these mixed solutions is important for determining the ideal ratio of each alcohol for future use in direct alcohol fuel cells.Based on the study of different ratios of ethanol and methanol mixtures, Wongyao et al. 23 concluded that the PtRu/C electrocatalyst was more efficient than the PtRu-PtSn/C electrocatalyst for mixed solutions in direct alcohol fuel cells. However, in all of the cases, the solutio...

PtSn Electrocatalyst Supported on MWCNT‐COOH: Investigating the Ethanol Oxidation Reaction

“…Hence, the formation of segregated phases in the electrocatalyst was due to the functionalization of the carbon nanotube support, which increased the affinity of Pt, facilitating interactions with the metal and interfering with the formation of the alloy. For untreated Vulcan XC 72 (used in this work), there is no specific anchoring sites on its surface, and then this mechanism for nanoparticle supporting was not considered, because the interaction between metal‐metal is favored and an electrocatalyst with 91–92 % Sn alloyed with Pt was obtained when using this carbon support and the same preparation method …”

“…The influence of the support has also been considered on the electrocatalyst properties. Based on a previous work, the polymeric precursor preparation method was used to produce a Pt 3 Sn electrocatalyst supported on Vulcan® carbon, and the Pt 3 Sn alloy formation was 91–92 %. In this work, the same preparation method was used, but the obtained electrocatalyst had only 32 % alloy phase.…”

“…The use of MWCNT‐COOH affects the morphology and structure of the electrocatalyst, favouring SnO 2 formation segregated with Pt (68 %) compared to 32 % in the Pt 3 Sn/C alloy formation. Previous work achieved 91–92 % Pt 3 Sn alloy on Vulcan® carbon using the same preparation method. The Pt 3 Sn 2 /MWCNT‐COOH had larger EASA, lower onset potential and higher normalized peak current for the EOR.…”

“…Therefore, this work aims to study a Pt 3 Sn 2 /MWCNT‐COOH electrocatalyst prepared by the polymeric precursor method at a metal load of 20 % (w : w) on the support for the ethanol oxidation reaction. Additionally, observing its physico‐chemical properties and the electrocatalytic activity related to the studied materials in previous work obtained from the same prepared method conditions but a different support. The presence of oxygen and carboxylate functional groups was analysed by FTIR in transmittance mode, and the wettability was analysed by contact angle measurements.…”

Ethanol Electrooxidation at Platinum-Rare Earth (RE = Ce, Sm, Ho, Dy) Binary Alloys

“…The advantage of alloy structures is no longer required to be proven, with numerous binary structure already tested; for example, Pt-M, with M = W, Pd, Rh, Re, Mo, Ti, Ce, Mn, Ni, and Cu always demonstrating a higher EOR activity than pure Pt as an anode catalyst [48,[67][68][69][70][71][72][73][74].…”