Fluoride effect on the electrochemical behaviour of the Fe(III)/Fe(II) system in H3PO4+H2O+HF

Electrochemical behaviour of iron ions on a gold electrode in H3PO4 and in H3PO4–HF solutions was studied to access the influence of fluoride ion on the electrochemical properties. Voltammetric and potentiometric studies showed that the Fe(III)/Fe(II) system in H3PO4–HF is generally reversible. This reversibility decreases when HF is added. ffusion coefficient of iron ions was determined in different media with and without HF at 20, 40 and 60°C. Comparisons between complexed species in phosphoric solutions with or without HF have been made. UV-spectra in different media show that there is no evidence of a new iron-fluoride complex, but a Fe–O–P–F bond is discussed.