Oxygen reduction on stepped platinum surfaces in acidic media

Oxygen reduction on Pt single crystal surfaces has been studied in acidic media using a hanging meniscus rotating disk electrode configuration to understand the effect of crystal orientation of the electrode toward electron transfer reactions. The surfaces used belong to the [ 1 1 ¯ 0 ] zone that can be classified in two different series, i.e. surfaces with (1 1 1) terraces separated by monatomic (1 1 0) steps and surfaces with (1 1 0) terraces and (1 1 1) steps. Both in sulphuric and perchloric acid solutions, the Pt(1 1 1) surface showed the lowest catalytic activity among those studied. Conversely, in agreement with the results reported previously on Pt surfaces belonging to the [ 0 1 1 ¯ ] zone [M.D. Macia, J.M. Campina, E. Herrero, J.M. Feliu, J. Electroanal. Chem. 564 (2004) 141], stepped surfaces, irrespectively to their step site symmetry, show higher catalytic activity on oxygen reduction than those on basal low-index surfaces. The effect on the structure sensitivity on the electrocatalytic activity is discussed in relation to the role of adsorbed species, such as hydrogen, oxygen, OH, electrolyte anions and oxide formation.