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...