l~lb~ el bu~rgrmic Chemi,~lr~' aml Catra!vsix, EindhoPen tJni,~6(1~) MB Eimlhocen. Netherlands Received 16 December 1Ot)0; revised 31 January 1997 AhsiraelThe: c~,clroca|alyliqr |vdBcIion of uilrale has been investigated on Pt, Pd and Pl k Pd elecu~od¢,~ covered wi|h a ,~ubmonolayeJ of gern~aniunk PI + Pd eleo,~des were prepared by electrol¢~s deposition of stubmnnolayer~ of Pd on Pl by exchange of PdCI~ for preadsod~ed eopl~,r, Underpote~ ~i,dly deposited germanium enhances the reduction rale of nitrate strongly. The reduction of nitrite i~ euhanced to a lesser extent, whezeas germanium is inactive for NO and hydroxylamine reduction. Furlher. cyclic voltammetry shows that the well known inhibition of the nitrate reduction at low potentials is absent fi~r germaniumomodified electrodes. Amperometry shows lhat the cun~nt densities for nitrate reduction at 0.1 V depend strongly on the composition of the electrode surface. The activities increase in the order Pd, PI and Pt + Pd and all electrodes display a plopurtional relation between the activity and the germanium coverage. This shows that gemmnium is involved in the rate determining step, which is the reduction of nitrate to nitrite and its role is to bind the oxygen atom of nitrate, The higher activities for Pt + Pd electrodes can be understood in terms of changes in the electronic structure of the metals as a result of alloying. Selectivity measurements with a rotating ring-disk electrode have shown for all electrodes that the hydroxylamine selectivity increases for increasing germanium coverage. Pd displays higher hydroxylamine ,;electivides than Pt and Pt + Pd electrode~. No gaseous products were observed for Pi. whereas for Pt + Pd and Pd N~O selectivitie~ up to 8% were found. © 1997 Elsevier Science S.A.

The Electrocatalytic Reduction of NO 3 − on Pt, Pd and Pt + Pd Electrodes Activated with Ge.-The presence of underpotentially deposited Ge on Pt or Pd electrodes enhances the reduction rate of nitrate strongly and that of nitrite to a lesser extent, but is inactive for NO and NH 2 OH. The well known inhibition of nitrate reduction at low potentials is absent in the presence of Ge. The activity of the electrodes increases in the order Pd ¡ Pt ¡ Pt + Pd. All electrodes display a proportional relation between the activity and Ge coverage indicating that Ge is involved in the rate determining step. -(GOOTZEN, J. F. E.; PEETERS, P. G. J. M.; DUKERS, J. M. B.; LEFFERTS, L.; VISSCHER, W.; VAN VEEN, J. A. R.; J.