Pt nanoparticles in polyelectrolyte multilayers: Polymer effects on the electrocatalytic activity for methanol oxidation

Abstract

The layer-by-layer (LbL) self-assembly technique is a simple and versatile tool for the controlled chemical conversion of metal ions into nanoparticles. In this work, we prepared LbL thin films containing Pt nanoparticles electroactive towards electro-oxidation of methanol by a two-step process, involving the exchange of different Pt precursor ions into the film, followed by their chemical reduction. We addressed the influence of the Pt precursor (Pt(NH3)42+ and PtCl62−) and polyelectrolyte-pairs (poly(diallyldimethylammonium chloride) (PDDA)/Nafion and poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA)) on the properties and electrocatalytic activity of the nanoparticles. NPs synthesized from Pt(NH3)42+ outperformed those growth from PtCl62−, the precursor used in previous works to prepared Pt NPs within LbL films. The combination of Pt(NH3)42+ and PDDA/Nafion films produced the best electrocatalytical performance with a specific activity of 0.8 mA.cm−2Pt. By varying the number of exchange/reduction cycles (n) between 1 and 5, a marked increase in the catalytic activity was observed for the first 2 cycles, followed by a saturation regime. The peak potential of the Pt/Pt oxide peak also increases in the first cycles and approaches a constant value close to that of a bulk Pt electrode coated with PDDA/Nafion. These behaviors are explained in terms of a strong polymer-Pt surface interaction that decreases with increasing n and stabilizes for n > 2.