Pulsed bipolar electrodeposition of palladium onto graphite powder

The pulsed bipolar electrodeposition of palladium onto 1-2 mum graphite par ticles was investigated. The amount of palladium deposited was strongly cor related with field intensity, showing an abrupt increase at 2-3 kV/cm. The electrodeposition was successful for frequencies ranging from 500 Hz to 20 kHz, and the amount of deposited palladium was independent of the frequency used. These results demonstrate that the preparation of bipolar electrodep osited catalysts can be achieved within a very large frequency window. Pall adium surface area measurements indicate an increase in dispersion with inc reasing frequency. Sonication of the graphite prior to deposition leads to significantly greater palladium dispersion. Electron microscopy characteriz ation reveals three types of growth: surface-bound, ramified, and amorphous . The surface-bound growth appears as spherical deposits on the order of 5 nm in both do and pulsed-field experiments. The ramified deposits consist o f interconnected 25-50 nm diam spherical structures extending from the grap hite particles and appear in the samples prepared at all studied frequencie s. (C) 2001 The Electrochemical Society.