Abstract
The performance of Pd electrocatalysts for formic acid electrooxidation was improved by application of metal oxide-multiwall carbon nanotubes composites as a catalyst support. Hybrid oxides/MWCNTs were synthesized by two different methods: chemical reduction method and impregnation method. Pd based catalysts were synthesized by polyol method on the MWCNTs or oxide/MWCNTs composites. The In2O3was deposited on MWCNTs by impregnation method (In2O3/MWCNTs-IM support) and in the presence of NaBH4(In2O3/MWCNTs-NaBH4support). The physical properties of the Pd/In2O3/MWCNTs-IM, Pd/In2O3/MWCNTs-NaBH4, Pd/SnO2/MWCNTs, and Pd/MWCNTs catalysts were characterized and their electrocatalytical performance in formic acid oxidation was compared. During Pd deposition on In2O3/MWCNTs-NaBH4support, InPd2structure was formed as observed by XRD. The electrochemical tests indicate that the two Pd/ In2O3/MWCNTs electrocatalysts have higher electrocatalytic activity than those of Pd/SnO2/MWCNTs and Pd/MWCNTs. The best performance was observed for the catalyst obtained by In2O3impregnation of MWCNTs denoted by Pd/In2O3/MWCNTs-IM.
Highlights
Growing environmental pollution and the fact that crude oil resources are going to be exhausted stimulate an intensive development of work on replacing petroleum fuels by biofuels and by application of fuel cells for production of electricity
For AO-Multiwalled carbon nanotubes (MWCNTs), both functional groups and defects on the surface formed by the acid oxidation lead to an increase of D/G intensity ratio [20]
The MOS modified MWCNTs, SnO2/MWCNTs, and In2O3/ MWCNTs were successfully synthesized by the impregnation method
Summary
Growing environmental pollution and the fact that crude oil resources are going to be exhausted stimulate an intensive development of work on replacing petroleum fuels by biofuels and by application of fuel cells for production of electricity. DFAFC has a number of advantages over direct methanol fuel cells [1]: (i) it has higher power density and higher energy efficiency, (ii) crossover flux of formic acid through Nafion membrane is several times smaller than that of methanol [2], and (iii) formic acid is less toxic than methanol and does not have the risk of producing hazardous by-products during oxidation (e.g., formaldehyde). While some of the catalysts are poisoning resistant in the long term, their activity is still too low and developing novel electrocatalysts is still crucial for their practical applications in DFAFC. One of the most promising approaches, improving activity and stability of the catalysts, was modification of carbon support (carbon black, MWCNTs) with metal oxides. It was demonstrated that Pt/In2O3/C has higher activity towards ethanol oxidation than that of Pt/C, and the enhancement of activity could be attributed to the effects of In2O3 adjacent to Pt (bifunctional effect) [52]
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