Surface structures at the initial stages in passive film formation on Ni(111) electrodes in acidic electrolytes

The adsorption of sulfate or OH species and subsequent Ni(OH)(2) film growth on Ni(1 1 1) single crystal electrodes has been investigated using in situ infrared reflection absorption spectroscopy (IRAs) as well as scanning tunneling microscopy (STM). In a pH 3 sulfuric acid solution, STM images show that a well-defined Ni(1 1 1) surface with a (I x 1) lattice is exposed at -300 mV, while hexagonal close-packed images with an atomic spacing of 0.32 nm are grown on this electrode at 300 mV. On the other hand, IRAs results in a sulfuric acid solution (pH 3) reveal that an absorption band at 1116 cm(-1), which can be ascribed to v(S-O) symmetric stretching of sulfate anion on Ni(1 1 1) surface, starts to appear at -400 mV and develops its intensity with an electrode potential increase, while an absorption band at 930 cm(-1) begins to develop at 0 mV on Ni(1 1 1), Ni(1 0 0) and Ni(1 1 0) electrodes, which can be assigned to an in-plane delta(Ni-OH) bending vibration in Ni(OH)(2) passive film. (C) 2003 Elsevier B.V. All rights reserved.