Abstract
Recent studies indicate that metal-containing activated carbon fibers (ACF) are promising adsorbents for hydrogen storage applications. In these studies, Pd compounds were added to a petroleum precursor and formed into ACFs. Results showed that the molecular composition of the pitch had a significant affect on critical characteristics of the ACFs, such as pore size and Pd particle size. In an ongoing Department of Energy project, we are testing pitch precursors with carefully controlled chemical compositions in order to develop an optimum precursor for hydrogen storage applications. A low softening point pitch made by Marathon Oil is being separated into narrow molecular weight fractions using a dense gas extraction (DGE) process. In the current series of tests the heavier portion of the extracted pitch was used to prepare both undoped and Pd-doped carbon fibers. These fibers were activated over a range of temperatures to determine the effect of temperature and pitch composition on ACF properties. Lower activation temperatures resulted in increased microporosity (desirable for hydrogen adsorption) for all Pd-doped pitch precursors. Comparing ACFs produced from various DGE-extracted pitches showed that even small quantities of mesophase-forming components inhibited activation and significantly reduced microporosity. Additional DGE pitch fractions are now being tested to further refine the optimum composition for hydrogen storage applications.
