Inducing a Cationic Response in Poly(pyrrole) Films

The redox processes of hexacyanoferrate doping anions inside thick poly(pyrrole) (PPy) layers are considered to be linked to the oxidation state of the PPy. Charge compensation of the PPy can be provided by the influx/efflux of anions and cations or through the Fe(CN)63–/4– oxidation level. In addition it has been proposed that polypyrrole exhibits an appreciable ion conductivity and anion permselectivity in the oxidized state, whereas the reduced state is more associated with cation permselectivity so long as the anionic groups are immobilized within the polymer. This article investigates whether a polypyrrole film containing hexacyanoferrate ions (PPyFeCN) can be used to visualize cation selectivity when the Fe(CN)63–/4– activity is seen. Using this method, it is shown that the permselectivity of the membranes is dependent on the electrolyte solution, and both cation and anion exchange occurs, therefore the response of the poly(pyrrole) layers depends on the electrolyte solution. However, the modification of the polymer surface by applying a thin Nafion film improves cation exchange with a selectivity which is possibly determined by size exclusion and electrostatic repulsions. A more selective potassium response was obtained after modification with a thin PVC based membrane containing valinomycin, selective for potassium. A potential step redox switching regime was proposed to make an initial assessment of the effect of K+ concentration on the current signal recorded. The electrode obtained responded to potassium in a range 10–7–3M K+, but appeared to result from a rather complex mechanistic pathway which requires further investigation.