Influence of triethylamine on the anodic dissolution characteristics of Ni,Cu and their alloys in non-aqueous solvents containing fluoride media: voltammetric and surface morphologic study

Multisweep cyclic voltammetric (CV) responses of nickel, copper, Monel and nickel–copper alloy had been extensively studied and compared in different non-aqueous solvents, such as acetonitrile (AN), propylene carbonate (PC) and sulpholane-containing anhydrous hydrogen fluoride (AHF) medium in the absence and the presence of triethylamine (Et₃N). The quantity of dissolution and surface morphological transformation on the electrodes as a result of anodic polarisation were investigated by means of atomic absorption spectroscopy and scanning electron microscopy (SEM), respectively. The CV study indicates that Ni, Cu and their alloys are highly unstable in AN/AHF medium. Surface morphology of Ni after polarisation in this medium reveals the generation of number of pits, whereas the evolution of small crystallites of CuF₂ is noted on the polarised alloy material, as evidenced by SEM pictures. The dissolution characteristics decrease significantly in PC/AHF medium and become low in sulpholane-containing fluoride medium on the four electrodes. The relative solubility of metal fluoride film in the three solvents increases in the order: sulpholane < PC < AN. The voltammograms suggest that addition of Et₃N (0.5 M) to AN- and PC-containing AHF medium helps both in maintaining uniform dissolution and generating compact fluoride film on the electrode surface. The addition of Et₃N to AHF/sulpholane medium shows only little influence in improving the electrocatalytic oxidation process.