K.-M. Mangold

Platinum distribution and electrocatalytic properties of modified polypyrrole films

Abstract For the preparation and modification of conducting polymer films as electrocatalysts for anodic hydrogen oxidation three pathways were investigated: (i) cathodic deposition of platinum from a hexachloro-platinum complex [PtCl 6 ] 2− on the pre-synthesised polymer film, (ii) incorporation of colloidal platinum particles into the polymer film during electropolymerisation and (iii) incorporation of a tetrachloro-platinum complex [PtCl 4 ] 2− during the electropolymerisation as counter ion and its subsequent cathodic reduction. Using SEM and EDX the distribution of platinum in the polypyrrole film depending on the preparation conditions was studied. The catalytic activity of the modified films was derived from polarisation curves of hydrogen oxidation using rotating disk electrode technique.

Conducting polymers as ion-exchangers for water purification

The charging and discharging processes of conducting polymers, e.g. polypyrrole, are accompanied by the exchange of ions. This effect was used for the development of an electrochemically switchable ion-exchanger for water purification, especially for softening drinking water. The ion-exchange behaviour and capacity of electrochemically and chemically prepared polypyrrole (PPy) in dependence on the incorporated counterions are characterised using an electrochemical quartz crystal microbalance and cyclovoltammetry. An ion-exchanger electrode based on modified PPy-nanoparticles was tested in a laboratory loop. The ion concentrations of the test solutions treated were investigated by atomic absorption spectroscopy and ion-selective electrodes with respect to an application for softening drinking water.

Preparation and Properties of Composite Polypyrrole/Pt Catalyst Systems

Three different methods for the preparation and modification of conducting polymer/noble metal catalyst systems consisting of polypyrrole (PPy) and platinum (Pt) are described for the anodic oxidation of methanol. The first method consists of the electrochemical deposition of a thin PPy film on glassy carbon substrate, which is modified with Pt either by electroreduction of hexachloroplatinate, codeposition from a nanodispersed Pt solution, or incorporation of tetrachloroplatinate as counterion followed by cathodic reduction. A second method is based on the preparation of nanoscale PPy(PSS) particles by chemical polymerization with polystyrenesulfonate PSS– as the counterion. This material is a favorable catalyst support for nanodispersed Pt due to its mixed electronic and cationic conductivity. To study the electrochemical properties, the particulate system PPy(PSS)/Pt is fixed in a carbon fiber electrode. A third method was developed which brings the polypyrrole in close contact to a proton exchanger membrane (Nafion) using a special chemical deposition procedure. This method is useful for preparing a membrane electrode assembly (MEA) consisting of Nafion/PPy/Pt. The structural, morphological, and electrocatalytic properties for methanol oxidation were studied depending on the preparation method applied using surface analytical techniques (TEM, SEM, and EDX) and electrochemical measurements (cyclic voltammetry and transient techniques).