Impedance response of electrochemical interfaces: part II-chemisorption.

Physical modeling helps to acquire fundamental insights from experimental data when electrochemical impedance spectroscopy is employed for mechanistic understandings of electrocatalytic reactions. Herein, we report an analytical model for chemisorption impedance with a consistent treatment of ion transport in the solution and electron transfer on the electrode surface. Our formulation avoids bothdecoupling of double-layer charging and electron transfer reaction, and a strict separation of double-layer charging and ion transport. Ion transport in the entire solution region is described by the Poisson-Nernst-Planck theory and electron transfer kinetics on the electrode surface by the Frumkin-Butler-Volmer theory. Surface dipoles caused by partially charged chemisorbates are considered. The classical Frumkin-Melik-Gaikazyan model for chemisorption is retrieved as a limiting case. The obtained formula is validated using experimental data of hydrogen adsorption at Pt(111). Characteristic frequencies and asymptotic behaviors of chemisorption impedance are analyzed.