Nitrate reduction catalyzed by underpotentially deposited Cd on Au(111): Identification of the electroactive surface structure

The electrocatalysis of the nitrate reduction to nitrite by Cd underpotenti al deposition (upd) on Au(111) was studied. The structures of the Cd adlaye r underpotentially deposited on a Au(111) surface with nitrate in acidic so dium sulfate electrolyte were investigated by scanning tunneling microscopy (STM). Several ordered adlattices were observed, with the catalytically ac tive structure being a (1 x 1) Cd adlayer. This adlayer exhibited a Moire p attern rotated by 9 degrees from the Au(111) lattice direction. Thiocyanate and ethanethiol were used to investigate the mechanism of the catalysis by the Cd adlayer. The addition of thiocyanate did not affect the nitrate red uction activity. On the of her hand, ethanethiol was a poison toward the ni trate reduction. STM images revealed surface roughening due to ethanethiol at the potential of the reduction of nitrate. We suggest that nitrate assoc iation with the (1 x 1) Cd adlattice is a requirement for electroreduction activity.