Simplifying mechanistic impedances

Common simplifying concepts of chemical kinetics, such as rate-determining and preequilibium steps, can be used to simplify the formulation of the electrochemical impedance for reaction mechanisms. A general strategy for eliminating kinetic parameters of preequilibrium steps from the governing equations is presented, which enables simpler subsequent generation of the impedance spectra and associated equivalent circuits. Examples that are various subcases of a metal electrode with simultaneous hydrogen evolution and hydrogen adsorption into the metal are discussed. The relationship of the apparent charge-transfer resistance to the true charge-transfer resistance is discussed. Examples are given where the presence of adsorption is masked and may not be easily detected in an impedance analysis. (C) 2020 Elsevier Ltd. All rights reserved.