Pt/TiO<SUB>2</SUB>/Poly(vinyl sulfonic acid) Layer-by-Layer Films for Methanol Electrocatalytic Oxidation

Abstract

One major challenge for the widespread application of direct methanol fuel cells (DMFCs) is to decrease the amount of platinum used in the electrodes, which has motivated a search for novel electrodes containing platinum nanoparticles. In this study, platinum nanoparticles were electrodeposited on layer-by-layer (LbL) films from TiO2 and poly(vinyl sulfonic) (PVS), by immersing the films into a H2PtCl6 solution and applying a 100 microA current during different electrodeposition times. Scanning tunnel microscopy (STM) and atomic force microscopy (AFM) images showed increased platinum particle size and electrode roughness for increasing electrodeposition times. The potentiodynamic profile of the electrodes indicated that oxygen-like species in 0.5 mol L(-1) H2SO4 were formed at less positive potentials for the smallest platinum particles. Electrochemical impedance spectroscopy measurements confirmed the high reactivity for the water dissociation and the large amount of oxygen-like species adsorbed on the smallest platinum nanoparticles. This high oxophilicity of the smallest nanoparticles was responsible for the electrocatalytic activity of Pt-TiO2/PVS systems for methanol electrooxidation, according to the Langmuir-Hinshelwood bifunctional mechanism. Significantly, the approach used here combining platinum electrodeposition and LbL matrices allows one to both control the particle size and optimize methanol electrooxidation, being therefore promising for producing membrane-electrode assemblies of DMFCs.

Self-assembled films from chitosan and poly(vinyl sulfonic acid) on Nafion® for direct methanol fuel cell

“…This technique allows for control of the thickness of the deposited thin films, thereby avoiding significant enhancement in the resistance of the chitosan/PVS/Nafion ® membrane and maintaining a low ohmic drop in the DMFC. [11][12][13][14] PVS was chosen because its sulfonic groups can interact with the protonated amine groups of chitosan, thus promoting decreased methanol permeation due to the less connected hydrophilic channels in the resulting LbL film. This may be exploited as an approach for hindering the crossover effect since it should reduce cell depolarization and cathode poisoning.…”