Selective electrocatalysis of ammonia oxidation on Pt(100) sites in alkaline medium

The oxidation of ammonia on platinum surfaces is a sensitive-structure reaction that takes place almost exclusively on Pt containing (1 0 0) sites. However it is strongly inhibited on Pt(1 1 1) and Pt(1 1 0) surfaces. A study using stepped electrodes with Pt(1 0 0) terraces and monoatomic Pt(1 1 1) steps, Pt(S) [n(1 0 0) x (1 1 1)], Miller indices Pt(2n - 1, 1, 1), shows that the activity of the electrode is strongly dependent on the terrace width, i.e., the wider the terrace the less positive the peak potential for ammonia oxidation. The change in the peak potential from the widest (1 0 0) terraces to terraces 6 atoms wide, i.e., from Pt(1 0 0) to Pt(11, 1, 1), is approximately 60 mV. This result is unexpected if we bear in mind the size and geometry of the ammonia molecule. (C) 2002 Elsevier Science B.V. All rights reserved.