Abstract
The growth of polypyrrole (Ppy) layers on gold electrodes in nearly neutral pH solutions is analysed using “in situ” voltametric and ellipsometric techniques. Different film structures are obtained depending on the potentiodynamic programme and the composition of the electrolyte. More compact dodecylsulphate-(DS) doped Ppy layers were grown at 1.2 V versus RHE than those obtained by applying a higher potential. The more compact layers correspond to the growth of an oxidised Ppy/DS layer that shows low pseudo capacity behaviour. After dipping, the doped Ppy/DS film in KCl solution-significant variations in optical indices and thickness are detected as a function of the applied potential. Higher electrochromism as well as decrease in film thickness after cathodisation is achieved. The optical indices and the thickness of the Ppy layer formed under different applied potential/time programmes are estimated.
Highlights
More compact dodecylsulphate-(DS) doped Ppy layers were grown at 1.2 V versus reversible hydrogen electrode (RHE) than those obtained by applying a higher potential
The Ppy/SDS electrode recently dipped in KCl solution adjusts spontaneously to an open circuit potential of about 0.88 V. These results show that even polarised at 0.1 V the Ppy/SDS layer grown at 1.2 V remains highly oxidized, and the cycling in Figure 2(a) corresponds to a switching between highly oxidized states with a scarce Ppy network
The Ppy/SDS layer grown by successive potential pulses shows an initially low optical index n − ik, and thickness di of about 100 nm
Summary
Conducting polymers and polypyrrole, Ppy, is extensively used in sensors, oxygen sensing, microelectronic mechanical systems MEMS, metal-insulator-semiconductor field effect transistors, drug release, actuators, water treatment, protective coatings against corrosion, and analytical displays [1,2,3,4,5,6,7,8,9,10,11,12,13]. The presence of different ions in the electrolyte modifies the layer growth rate, the voltametric response, and the interfacial capacity These effects are related to variations in pyrrole absorption, concentration of radicals, structure of the oligomers initially formed during anodisation, and partial water exchange taking place together with ion’s uptake processes into the membrane [23,24,25]. The Ppy matrix in the reduced state is electroneutral and a poor ionic and electronic conductor The properties of these membranes can be modified by doping the Ppy with large and bulky shaped anions such as dodecylsulphate, dodecylsulphonate, paratoluensulphonate, and so forth. Cyclic voltammetry and ellipsometry were used to investigate the effect of the potential on the growth of doped Ppy/DS layers
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