Engineering ionic and electronic conductivity in polymer catalytic electrodes using the layer-by-layer technique

The platinum loading, electronic and ionic conductivity, tuned porosity, and electrode potential of layer-by-layer (LBL) conducting polymer films for thin film catalytic electrodes are presented. Films of polyaniline (PANi)/poly(acrylic acid) (PAA) or PANi/poly(acrylic acid)-co-polyacrylamide (PAA-co-PAAm) of 3.0-mu m thickness were pH-tuned to induce porosity as they were assembled. Three different techniques were used to dose the LBL PANi films with platinum. The first method used reductive precipitation of platinum and ruthenium salts adsorbed within LBL films of PANi/PAA-co-PAAm. The second method, termed polyelectrolyte colloidal platinum stabilization, was applied to load platinum nanoclusters into LBL films of either PANi/PAA or PANi/poly(styrene sulfonate) films. The third method used a PANi/platinum powder dispersion to load platinum crystals into LBL films of PANi/PAA-co-PAAm or poly(2-acrylamido-2-methyl-1-propane sulfonic acid) (PAA-co-PAMPS). The first method yielded the best metal loadings with maximum platinum loadings of 0.3 mg cm(-1), and the resulting Pt-containing PANi/PAA-co-PAAm films were further examined for their electrochemical characteristics. The electrode potential and chronopotentiometric current control in the resulting electrodes were examined for the best-performing LBL PANi film assembled in this study. The catalyzed PANi/PAA-co-PAAm electrodes exhibited an electrode potential similar to that of pure platinum, a relatively high and stable electrical conductivity of 2.3 S cm(-1), and an ionic conductivity of up to 10(-5) S cm(-1).