Electrosynthesis of a novel polyindole derivative from 5-aminoindole and its use as catalyst support for formic acid electrooxidation

A novel conducting polymer, poly(5-aminoindole) (PAIn), one of polyindole derivatives, has been electrosynthesized by potentiodynamic method in 0.5 M H2SO4 aqueous solution containing 0.02 M 5-aminoindole (AIn). As-synthesized polymer films show good electrochemical activity and stability in aqueous solution. 1H NMR, UV–visible and emission spectral analyses confirmed the formation of the polymer with conjugated chain structure and that the polymerization mainly occurred at C(2) and C(3) positions with NH2 and NH remaining intact. Based on as-prepared PAIn, a composite catalyst has been synthesized via electrodepositing Pt micro/nano-particles on the polymer modified carbon cloth (CC) electrode. As-formed composite catalysts were characterized by SEM, EDX and electrochemical analyses. Compared with pure Pt particles, the Pt/PAIn composite catalyst deposited on CC electrode (denoted as Pt/PAIn/CC) shows higher catalytic activity and stronger poisoning-tolerance for formic acid electrooxidation. Electrochemical impedance spectroscopy shows that the charge-transfer resistance for formic acid electrooxidation on Pt/PAIn/CC is smaller than that on Pt/CC. The present study shows a promising conducting polymer, PAIn, used as the catalyst support for formic acid electrooxidation, and further work on improving the catalytic activity of the composite catalyst is under way.

► PAIn was electrosynthesized in aqueous solution.
► As-synthesized polymer shows good electrochemical activity and stability.
► Pt particles were electrodeposited on PAIn film to prepare a composite catalyst.
► The composite catalyst shows high catalytic activity for formic acid oxidation.