pH effect on acetate adsorption at Pt(111) electrode

Abstract pH effect on thermodynamics and kinetics of acetate adsorption on the Pt(111) electrode in solutions is studied over a wide pH range (from 1 to 13) by cyclic voltammetry and electrochemical impedance spectroscopy. With increasing solution pH i) from pH = 1.1 to 4.7, the peak potential for acetate adsorption shifts slightly from 0.39 V RHE to 0.46 V RHE , ii) from pH = 4.7 to 10.2 it shifts by ca. 56 mV/pH unit; iii) the adsorption isotherm for acetate adsorption does not show obvious changes, but the adsorption kinetics become slower with pH changing from 1.1, 4.7 to 7.6. The positive shift in the acetate adsorption peak with pH (on the RHE scale) can be explained by the pH-dependence of the thermodynamic equilibrium potential for acetate adsorption with either acetic acid or acetate anions as the precursor. The faster acetate adsorption kinetics in acid than in alkaline solution are attributed to a reduced activation barrier, owing to the formation of hydrated H + upon CH 3 COOH deprotonation to adsorbed acetate.