Investigation of the surface properties of platinum,rhodium and iridium electrodes in hydrofluoric acid solutions

The charging curves, the potentiodynamic curves and the isoelectric potential shifts have been measured on Pt, Rh and Ir electrodes in HF and HF + KF solutions in a Teflon cell. From the obtained data, the Γ_H⁺?? curves and the Δσ?? curves of the first kind have been calculated by means of the thermodynamic theory of the hydrogen electrode. The Γ_H⁺ values in 0.14 M HF and 0.3 M HF + 0.12 M KF are much less than in 0.005 M H₂SO₄ and 0.005 M H₂SO₄ + 0.5 M K₂SO₄ solutions. In the presence of F^? anions, the potentials ?_ε=0 and ?_Q=0 are by 25–55 mV more anodic than in the presence of SO^2?₄ anions. In an acidified fluoride solution the values of σ are higher than in an acidified sulfate solution. The analysis of the results obtained leads to the conclusion that on platinum metals the fluoride anions in the ?_r region investigated (from ?_r = 0 to ?_r = 900 mV) are the most weakly adsorbed anions.