Separation and Purification Technology, Vol.80, No.3, 526-532, 2011
Increasing the activity and stability of chemi-deposited palladium catalysts on nickel foam substrate by electrochemical deposition of a middle coating of silver
The objective of this study was to enhance the activity and stability of the chemi-deposited palladium/nickel foam (Pd/Ni foam) electrode used in the electrochemical dechlorination process. The electrochemical deposition of silver onto a nickel foam substrate (Ag/Ni foam) was applied before the chemical deposition of palladium. The physicochemical properties of the resultant material (Pd/Ag/Ni foam) were characterized by X-ray diffraction and scanning electron microscopy. The results showed that the silver coating was in the form of spherical apophyses, and the palladium was dispersed finely on the surface of the Ag/Ni foam. Dichloroacetic acid was selected as an indicator to evaluate the activity and stability of the palladium catalyst. Pd/Ag/Ni foam electrode consistently had relatively higher dechlorination rate and current efficiency (CE) in the current density range of 1.5-10.5 mA cm(-2) compared to the Pd/Ni foam electrode. Quantitative analysis of the main intermediates and final products involving monochloroacetic acid, acetic acid and the chloride ion further demonstrated the enhancement of electrochemical dechlorination by the presence of silver. Moreover, after five cycles of dechlorination, the CE for the Pd/Ni foam electrode decreased dramatically from 67% to 13%, whereas that for the Pd/Ag/Ni foam electrode was decreased by much less, from 78% to 62%, and the palladium loss was clearly reduced by the addition of a silver coating between the Ni foam and the Pd outer layer. (C) 2011 Elsevier B.V. All rights reserved.