Abstract
The direct alcohol fuel cell is a kind of power generation device that directly converts the chemical energy of small molecule alcohols into electric energy. In this paper, the electro-oxidation behaviors of some typical alcohols (methanol, ethanol, ethylene glycol, n-propanol, 2-propanol, and glycerol) over Pt, Pd, and Au electrodes were investigated in acidic, neutral, and alkaline media, respectively. By analyzing the activity information from a cyclic voltammetry (CV) method and some dynamic tests, several regularities were revealed in those electro-oxidation behaviors. Firstly, alkaline media is the best for the electro-oxidation of all these alcohols over Pt, Pd, and Au catalysts. Secondly, the hydrogen bond donation abilities (HBD) of different alcohols were found have a great relationship with the catalytic performance. In alkaline media, on Pt electrodes, the solute HBD is positively correlated with the ease of electrooxidation within the scope of this experiment. Contrarily, it is negatively correlated on Pd and Au electrodes. Additionally, for Pt catalysts in acidic and neutral media, the relationship becomes negative again as the HBD increases. Finally, the alcohol’s molecular structure properties were found to have a remarkably influence on the activity of different catalysts. Over the Pt electrode in alkaline media, the activation energy of methanol oxidation is 44.1 KJ/mol, and is obviously lower than the oxidation of other alcohols. Under similar conditions, the lowest activation energy was measured in the oxidation of n-propanol (14.4 KJ/mol) over the Pd electrode, and in the oxidation of glycerol (42.2 KJ/mol) over the Au electrode. Totally, among all these electrodes, Pt electrodes showed the best activities on the oxidation of C1 alcohol, Pd electrodes were more active on the oxidation of C2-3 monobasic alcohols, and Au electrodes were more active on the oxidation of polybasic alcohols.
Highlights
Direct alcohol fuel cells (DAFCs) generate electric power by feeding liquid fuels directly to the anode, which have been recognized as green energy generators capable of converting renewable sourcesCatalysts 2019, 9, 387; doi:10.3390/catal9040387 www.mdpi.com/journal/catalystsCatalysts 2019, 9, 387 into electric power [1,2]
A cyclic voltammetry (CV) method was used to test the catalytic performance of these electrodes to discover some regularities of those electro-oxidation reactions
After comparing CV peaks for Pt electrodes in the three kinds of media, we found that the lowest onset potential and highest current density were mostly emerged in alkaline media, and the situation was contrary in neutral media
Summary
Direct alcohol fuel cells (DAFCs) generate electric power by feeding liquid fuels directly to the anode, which have been recognized as green energy generators capable of converting renewable sources. Methanol was most studied due to various advantages, the main problem of using methanol as a fuel for DAFCs is its high toxicity to the catalyst by the intermediate product in the oxidation process. One of the motivations for studying glycerol with three carbons is that they can be used in direct alcohol fuel cells for electric energy generation, in addition to the symbiosis of heat and chemicals. Claudio Bianchini and Pei Kang Shen [18] described and discussed many different types of anodes containing Pd-based electrocatalysts They found that Pd nanocatalysts exhibit higher activity for the electrooxidation of monohydric alcohols and polyols in alkaline media. In this paper, we attempted to investigate the electro-oxidation behaviors of some typical alcohols (methanol, ethanol, ethylene glycol, n-propanol, 2-propanol, and glycerol) over different electrodes in acidic, neutral, and alkaline media, respectively. A cyclic voltammetry (CV) method was used to test the catalytic performance of these electrodes to discover some regularities of those electro-oxidation reactions
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