The effect of arsenic on the electrodeposition of palladium from ethylenediamine-palladium (II) complex solutions.

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The effect of arsenic on the electrodeposition of palladium from ethylenediamine-palladium (II) complex has been investigated in neutral ethylenediaminetetraacetic acid solution. Addition of NaAsO2 made the palladium deposition potential more noble and the deposition rate faster, and deposits having a low rate of hydrogen occlusion were obtained with high current efficiency. At potentials of -0.68- -0.75V (SCE) on the cathodic current-potential curves for deposition of palladium by the addition of NaAsO2, the Tafel slope was -0.055V·decade-1 and the reaction order of palladium ion was 1. It is thought that the arsenic is adsorbed on the electrode surface as arsenic ions, and that the adsorbed arsenic ions appear to play the role of active sites (A). The following electrodeposition mechanism was inferred.Pd(en)22+soln+A Pd2+ads·A+2en (1)Pd2+ads·A+2e Pdads·A (2)Pdads·A Pdcrys+A (3-a)That is to say, Eq. (2) is the rate determining process in the deposition of palladium in solutions containing NaAsO2, and deposition current depends on the number of active sites (A), i.e. the concentration of NaAsO2 in the solution.
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