Synthesis of fibrous activated carbons and monoliths for hydrogen storage

Resumen

For a future energy sector, hydrogen is considered a clean alternative to other fuels. As an ideal secondary energy carrier it can be produced from renewable energy sources (e.g., solar, wind, biomass, etc.), and converted very efficiently to electricity in fuel cells, emitting only water. However, one of the main obstacles which impedes the introduction of this technology is the absence of efficient storage solutions. This is strongly related to the low density of hydrogen, which exists as a supercritical fluid under normal conditions. In order to use hydrogen as a fuel, a number of different technologies are considered today. Among them, the high pressure storage in adsorbent materials is a promising technology. The adsorbents for such kind of application require very specific features, depending on the thermophysical storage conditions. The overall research objective of this study was the synthesis and characterization of activated carbon fibers and nanofibers, as well as monoliths, in order to obtain suitable materials for hydrogen storage. The specific objectives of the research were: . Identify the optimal parameters of activation, in order to synthesize activated carbon fibers (ACFs) with suitable hydrogen storage characteristics. . Produce larger amounts of ACFs by up-scaling of the activation process. . To study the synthesis of activated carbon nanofibers (ACNFs). . To optimize the density of the ACFs and ACNFs by synthesizing monoliths from them. . Measure the adsorption of H2 on selected samples and evaluate their total storage capacities. . Estimate the capacities of H2 storage systems by taking into account the technical specifications of state-of-the-art H2 storage vessels. The main contribution of this work was the identification of the activation parameters for the synthesis of activated carbon fiber materials with tailored properties for hydrogen storage application. H2 adsorption measurements on ACFs confirm and consolidate results previously reported in the literature. Despite this, exceptionally high hydrogen adsorption amounts were measured for an ACNF at 298 K and 20 MPa. The total H2 storage capacity was established as a useful tool for material characterization. In addition, formulas have been developed for calculating the capacities of H2 storage systems. These formulas provide the opportunity to evaluate the performance of tanks and adsorbents for H2 storage via physisorption.