Crystallization kinetics of Pd in composite films of PEDT

The crystallization of palladium in poly-3,4-ethylenedioxythiophene (PEDT) films is studied in order to obtain nanosized palladium clusters in PEDT co mposite layers with high electrocatalytic activity. Nucleation and growth o f Pd is investigated for dependences on overpotential, polymer layer thickn ess d and chemical state (active or overoxidized) of the PEDT films. It is found that before the onset of diffusion limitations the growth occurs unde r charge transfer control. The observed induction period t(0) indicates cry stallization at the metal \ polymer interface. The linear relation I-1/3 ve rsus t found in the initial stage of the deposition process gives evidence for three-dimensional growth of the metal crystals. The number N-0 of sites active for nucleation decreases strongly with increasing d. A saturation i n N-0 is reached for continuous thicker films. The overoxidized layers are less active for metal deposition and exhibit a 50-fold lower number of acti ve sites. The electrocatalytic properties of the Pd/PEDT composite layers a re studied with respect to hydrogen sorption. High electrocatalytic activit y is found for composites obtained with thin PEDT films polymerized in the low potential region. (C) 2001 Elsevier Science B.V. All rights reserved.