Pulsed bipolar electrodeposition of palladium onto graphite powder

The pulsed bipolar electrodeposition of palladium onto 1-2 mum graphite particles was investigated. The amount of palladium deposited was strongly correlated 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 electrodeposited catalysts can be achieved within a very large frequency window. Palladium surface area measurements indicate an increase in dispersion with increasing frequency. Sonication of the graphite prior to deposition leads to significantly greater palladium dispersion. Electron microscopy characterization 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 of interconnected 25-50 nm diam spherical structures extending from the graphite particles and appear in the samples prepared at all studied frequencies. (C) 2001 The Electrochemical Society.