Short communicationElectro-oxidation of methanol, 1-propanol and 2-propanol on Pt and Pd in alkaline medium
Introduction
Direct alcohol fuel cells (DAFCs) based on methanol as fuel have attracted enormous attention as power sources for portable electronic devices and transportation due to the much higher energy density than gaseous fuels such as hydrogen and natural gas [1], [2]. However, the development of DAFCs based on methanol fuel is facing serious difficulties [3], [4]: (i) slow electro-kinetic of methanol oxidation, (ii) high-methanol crossover and (iii) high toxicity of methanol. Therefore, other alcohols were considered as alternative fuels. Here, the saturated C3-alcohols (1-propanol and 2-propanol) were investigated as the fuels for DAFCs. Especially, direct 2-propanol fuel cells have attracted more and more attention as 2-propanol is the smallest secondary alcohol, less toxic than methanol and its electrochemical oxidation is of great interest due to its particular molecular structure [5]. The direct alcohol fuel cells using 2-propanol as fuel show much higher performance than direct methanol fuel cells and a much lower crossover current [6], [7], [8].
Pt has been extensively investigated as the electrocatalyst for methanol, 1-propanol and 2-propanol electro-oxidation in acid medium [9], [10], [11], [12], [13]. However, Pt has a low activity for alcohol electro-oxidation in acid medium. If alcohol electro-oxidation proceeds in an alkaline instead of an acidic medium, the kinetics will be significantly improved [14], [15], [16], [17]. However, alkaline medium is not stable for DAFCs owing to the carbonation of alkaline electrolyte. Thus, to avoid the carbonation alkaline membranes should be used [18], [19], [20]. The DAFCs with alkaline membrane show reasonable performance stability.
A lot of work has been done to study the electro-oxidation of methanol, 1-propanol and 2-propanol on Pt-based catalysts in alkaline medium [21], [22], [23], [24]. However, the high price and limited supply of Pt constitute a major barrier to the development of DAFCs. Pt-free electrocatalysts such as Pd may be used as electrocatalysts for the methanol, 1-propanol and 2-propanol oxidation in alkaline medium. Pd-based electrocatalysts have been used for formic acid and hydrazine electro-oxidation in acid medium [25], [26], [27] and formaldehyde electro-oxidation in alkaline medium [28]. Our previous work on the development of Pt-free electrocatalysts for alcohol oxidation has focused on Pd-based catalysts and the results revealed that Pd is a good electrocatalyst for methanol and ethanol oxidation in alkaline medium [29], [30]. However, there is little information on the electrocatalytic properties of 1-propanol and 2-propanol oxidation on Pd catalyst in alkaline medium. Here, Pd will be investigated as electrocatalyst for 1-propanol and 2-propanol oxidation and compared with the conventional catalyst of Pt in alkaline medium. The study of alcohol oxidation on different catalysts may provide valuable data for development of new, high-active catalysts for alcohol electro-oxidation in alkaline medium.
Section snippets
Experimental
Methanol, 1-propanol, 2-propanol and KOH in this work were of analytical grade purity. The experiments were carried out at 25 °C in a temperature-controlled water-bath. All electrochemical measurements were carried out in a three-electrode cell using CHI 700C electrochemical workstation (CHI Instrument, Inc., USA). Solutions were freshly prepared and purged with nitrogen (99.999%) before each experiment.
The working electrodes were platinum and palladium disk (99.999%) with a geometrical area of
Results and discussion
Fig. 1 shows the cyclic voltammograms of methanol, 1-propanol and 2-propanol oxidation in 1.0 M KOH solution containing 1.0 M alcohol on Pt electrode. The sweep rate is 5 mV s−1 in the potential range from −0.9 V to 0.3 V. By comparing with the cyclic voltammogram in the absence of alcohol, an alcohol oxidation peak can be clearly observed. The electro-oxidation of alcohol on Pt electrode was characterized by two well-defined current peaks on the forward and reverse scans. In the forward scan, the
Conclusions
The preliminary results in the present study show that Pd is a good electrocatalyst for 1-propanol and 2-propanol oxidation. The activity order of alcohol oxidation on Pt electrode is methanol > 1-propanol > 2-propanol. The 1-propanol and 2-propanol oxidation shows a very low activity on Pt electrode in alkaline medium. The activity order of alcohol oxidation on Pd electrode is 2-propanol > 1-propanol > methanol. The 2-propanol oxidation shows the highest activity on Pd electrode in alkaline medium.
Acknowledgments
This work was financially supported by the Natural Science Foundations of China (20573136) and the Natural Science Foundations of Guangdong Province (07300877, 04205405 and 06023099).
References (32)
- et al.
J. Power Sources
(2002) - et al.
Electrochim. Acta
(2007) - et al.
J. Power Sources
(1999) - et al.
J. Electroanal. Chem.
(1989) - et al.
J. Power Sources
(2003) - et al.
J. Power Sources
(2003) - et al.
J. Power Sources
(2006) - et al.
J. Electroanal. Chem.
(1995) - et al.
Electrochim. Acta
(1996) - et al.
J. Electroanal. Chem.
(1999)