Review and theoretical analysis of ac-av methods for the investigation of hydrogen insertion Part II. Entry side impedance, transfer function and transfer impedance formalism

The formalism related to alternating current-voltage methods is reviewed, c ompleted and unified for hydrogen insertion in metals and alloys, in relati on to permeation cell membranes with potentiometric or potentiostatic detec tion of hydrogen and electrodes with impermeable boundary conditions. The e lectrochemical system representation in terms of an electrical dipole or qu adripole is first given to introduce the impedance on the entry side, the t ransfer impedances and the potential and current density transfer functions through the membranes, which can be used experimentally to investigate hyd rogen insertion. Next, the surface process is presented, taking the direct (one-step) insertion mechanism into consideration for the sake of simplicit y. Based on the surface process and diffusion formalisms, theoretical expre ssions are derived for the entry side impedance, transfer functions and tra nsfer impedances, depending on the electrode or membrane type and the bound ary conditions. (C) 2000 Elsevier Science S.A. All rights reserved.