Determination of the diffusion coefficient of an inserted species by impedance spectroscopy: application to the H/H x Nb2O5 system

Impedance spectroscopy, unlike large signal methods, allows the diffusion coefficient of an inserted species to be determined as a function of the electrode potential. The expression for the restricted linear diffusion impedance may be modified to empirically account for the difference of the electrochemical system behaviour from the ideal. It is then possible to estimate the diffusion coefficient of the inserted species from characteristic frequencies on the Nyquist diagrams and/or from the frequencies corresponding to the intersection of the asymptotes of the log (−Im Z), log f graphs. These estimations are independent of assumptions concerning the active area of the electrode. The method has been applied to the study of hydrogen insertion in H x Nb2O5.