Due to its many physisorption sites as well as chemisorption sites, polyaniline (PANI) has been investigated for hydrogen storage purposes. The PANI was produced in house via traditional chemical synthesis methods and then electrospun to produce fibers. These PANI fibers were investigated and compared with standard bulk PANI and found to be stable up to 150 degrees C. When investigating PANI fibers, using PCT measurements, it was found that a reversible hydrogen storage capacity of similar to 3-10 wt.% could be obtained at different temperatures. Hydrogen kinetic sorption measurements in prolonged cycles (up to 66 cycles) reveal an uptake and release of >6-10 wt.% on these PANI materials. The importance of the type of measurement is discussed as to its effect on the morphology and structure of the PANI nanofibers. The surface morphologies before and after hydrogen sorption on these PANI fibers encompass significant changes in the microstructure (nanofibrallar swelling effect). Detailed chemical and physical characterization of the PANI fibers is reported as part of this work. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.