Electrochemical impedance spectroscopy is one of the efficient methods for studying reaction mechanisms. In case of hydrogen evolution reaction, the transfer function involved is very complex. It is therefore usually obtained through indirect methods. First, a simple equivalent circuit is usually fitted to the experimental data using complex non-linear least square methods. The Circuit parameters thus obtained are then transformed to transfer function parameters. In the present approach, the procedure for obtaining transfer function has been simplified through its piecewise definition in various frequency ranges. A direct method to obtain transfer function using asymptotic analysis has been presented. The method to reduce error involved in the analysis has also been discussed. It has been shown that the approach will also be applicable for other systems. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.