A simple method for enhancing the catalytic activity of Pd deposited on carbon nanotubes used in direct formic acid fuel cells

Abstract

Palladium catalysts deposited on carbon nanotubes are used as the anode material in a direct formic acid fuel cell (DFAFC). In this paper we propose a simple method for enhancing the catalytic activity of Pd deposited on carbon nanotubes for formic acid electrooxidation by using ammonia solution. Multiwall carbon nanotubes (MWCNTs) used as the catalyst support are oxidized with concentrated nitric acid for 6 and 50 h. During the oxidation polynuclear aromatic compounds (PACs) are formed. We propose the use of ammonia solution after the oxidation process to remove the PACs from the carbon nanotubes surface. The properties of differently functionalized MWCNTs are studied and the results show that the use of ammonia solution removes the PACs formed during the oxidation process. The oxidation time of the carbon nanotubes has also a significant effect on the properties of the obtained catalysts. The palladium catalysts deposited on MWCNTs oxidized for a shorter time and rinsed with ammonia solution exhibit the highest initial activity in electrooxidation of formic acid in DFAFC (P = 216 mW mgPd−1).