Enhanced electrocatalysis of oxygen reduction on Se-Modified platinum single crystal electrodes

• Pt(hkl) electrodes are used as model electrodes to investigate the relation between different reaction sites and the ORR activity. • The Pt(hkl) electrodes display enhanced ORR electrocatalytic activity with Se modification. • Se adatoms enhance the ORR activity on the neighboring sites and inhibit the reaction on the deposition sites. Se-modified platinum single-crystal surfaces in the [ 01 1 ¯ ] zone have been used as model electrocatalysts for the oxygen reduction reaction (ORR). The results show that: (1) the Pt(hkl)-[n(111)×(100)] electrodes display enhanced ORR electrocatalytic activity with Se modification. (2) Se adatoms have a double effect on the ORR kinetics at model Pt electrodes: they enhance the activity on the neighboring sites and inhibit the reaction on the sites in direct contact with the Se adatoms. (3) The hydrophobicity and the altered electronic properties are probably the reasons for the enhanced electrocatalysis for ORR with Se modification. The positive shift of the potential of zero free charge of Pt(hkl)@Se electrodes compared to that of un-modified Pt(hkl) are in agreement with these interpretations. (4) At very low coverages, the promotion effect of Se modification on ORR activity at (100) sites is stronger than that at (111) sites, which is probably due to the more pronounced hydrophobicity of the former.