The present paper reports on A.C. impedance study of hydrogen evolution reaction (HER), carried-out on Pd-modified carbon fibre (CF) and nickel-coated carbon fibre (NiCCF) materials. The HER was examined in 0.5 M H2SO4 solution for electrochemically deposited Pd on Hexcel 12K AS4C CF and Toho-Tenax 12K50 NiCCF tow materials. Kinetics of the hydrogen evolution reaction was studied at room temperature, over the cathodic overpotential range: -100 to -1200 mV vs. RHE. Corresponding values of charge-transfer resistance, exchange current-density for the HER and other electrochemical parameters for the examined catalyst materials were derived. Thus, Pd modification of CF and NiCCF materials (at ca. 1.5 wt.% Pd) dramatically increased the exchange current-density parameter by about 5300x and 445x for carbon fibre and nickel-coated carbon fibre tows, correspondingly. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.