The Role of P in the Anodic Inhibition of an Amorphous Co‐20P Alloy in Acidic Electrolytes

Abstract

Anodic polarization of an amorphous Co‐20P alloy in deaerated or shows alloy dissolution to be inhibited at potentials between approximately −0.3 and 0.2 V (SCE), while pure crystalline Co dissolves readily and does not passivate at anodic potentials in either electrolyte. Analysis of Co‐20P surfaces by x‐ray photoelectron spectroscopy after anodic polarization reveals an enrichment of elemental P in the near‐surface region, the presence of approximately a monolayer of hypophosphite and phosphate ions on the surface, and a virtual absence of oxidized cobalt species. Thus, the Co‐20P alloy does not inhibit dissolution by the development of a three‐dimensional cobalt oxide film. A chemical process that is controlled by the formation and surface retention of hypophosphite anions is proposed. An identical passivation mechanism has been previously observed with an amorphous Ni‐20P alloy.