Abstract
Direct alcohol fuel cells (DAFCs) mostly use low molecular weight alcohols such as methanol and ethanol as fuels. However, short-chain alcohol molecules have a relative high membrane crossover rate in DAFCs and a low energy density. Long chain alcohols such as butanol have a higher energy density, as well as a lower membrane crossover rate compared to methanol and ethanol. Although a significant number of studies have been dedicated to low molecular weight alcohols in DAFCs, very few studies are available for longer chain alcohols such as butanol. A significant development in the production of biobutanol and its proposed application as an alternative fuel to gasoline in the past decade makes butanol an interesting candidate fuel for fuel cells. Different butanol isomers were compared in this study on various Pt and PtSn bimetallic catalysts for their electro-oxidation activities in acidic media. Clear distinctive behaviors were observed for each of the different butanol isomers using cyclic voltammetry (CV), indicating a difference in activity and the mechanism of oxidation. The voltammograms of both n-butanol and iso-butanol showed similar characteristic features, indicating a similar reaction mechanism, whereas 2-butanol showed completely different features; for example, it did not show any indication of poisoning. Ter-butanol was found to be inactive for oxidation on Pt. In situ FTIR and CV analysis showed that OHads was essential for the oxidation of primary butanol isomers which only forms at high potentials on Pt. In order to enhance the water oxidation and produce OHads at lower potentials, Pt was modified by the oxophilic metal Sn and the bimetallic PtSn was studied for the oxidation of butanol isomers. A significant enhancement in the oxidation of the 1° butanol isomers was observed on addition of Sn to the Pt, resulting in an oxidation peak at a potential ∼520 mV lower than that found on pure Pt. The higher activity of PtSn was attributed to the bifunctional mechanism on PtSn catalyst. The positive influence of Sn was also confirmed in the PtSn nanoparticle catalyst prepared by the modification of commercial Pt/C nanoparticle and a higher activity was observed for PtSn (3:1) composition. The temperature-dependent data showed that the activation energy for butanol oxidation reaction over PtSn/C is lower than that over Pt/C.
Highlights
Direct alcohol fuel cells (DAFCs) are promising alternative power sources and have advantages over hydrogen fuel cells for portable applications
In our previous study,[11] the activities of butanol isomers oxidation on Pt and Pd electrodes were studied in alkaline media and the reactivities were observed to be in the order of n-butanol > iso-butanol >2butanol > ter-butanol
A series of long chain C4 alcohols have been studied for electrochemical oxidation in acidic media on a Pt electrode
Summary
Direct alcohol fuel cells (DAFCs) are promising alternative power sources and have advantages over hydrogen fuel cells for portable applications. Second generation biofuels are proposed to be produced from nonfood based biomass feedstock such as lignocellulose biomass (LCB) (e.g., corn stover and fiber, wheat and barley straw, switchgrass, miscanthus).[7,8] The advantages of cellulose and lignin based feedstock are that they are abundant and can be considered as a waste product In this regard, butanol is considered a second generation biofuel, with better infrastructure compatibility and higher energy density than ethanol and are superior to ethanol as a fuel itself or as a gasoline additive.[7,8] biobutanol is nonpoisonous, noncorrosive, biodegradable and does not lead to soil and water pollution.[9]. Both electrodeposited PtSn and Sn-modified commercial Pt/C have been studied
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