In Situ Raman Studies on Cathodically Deposited Nickel Hydroxide Films and Electroless Ni−P Electrodes in 1 M KOH Solution

Three types of working electrodes, as-deposited nickel hydroxide, deactivated nickel hydroxide, and electroless Ni−P electrode, are studied in this work. The surface state of the electrodes varying with potential are investigated using cyclic voltammetry techniques combined with in situ Raman spectroscopy in 1 M KOH solution. As-deposited nickel hydroxide is electrooxidized to the oxides of higher state with Raman characteristic bands, 475 and 55 cm-1, and the corresponding reaction is assigned to be a α-Ni(OH)2/γ-NiOOH redox reaction in the potential range between 350 and 500 mV. When the film is deactivated by voltammetric cycling, the phases, β-Ni(OH)2, and some untransformed α-Ni(OH)2 are present. β-Ni(OH)2 will be electrooxidized to β-NiOOH, which has Raman characteristic bands of 480 and 560 cm-1 in the anodic sweep between 350 and 450 mV. The redox pair on the electroless Ni−P electrode is recognized as β-Ni(OH)2/β-NiOOH because of the identical Raman bands with β-NiOOH, namely, 480 and 560 cm-1, after being electrooxidized.