Highly-ordered Metal-modified Mesoporous Carbon Nitride: As a Novel Hydrogen Adsorbent

Development of hydrogen-fueled vehicles can bring economic and environmental benefits through decreased use of oil, and, consequently, a decrease in air pollution and other greenhouse gases.1 However, one of the most important drawbacks of the use of hydrogen as a fuel is that it has to be stored. There are different techniques to store hydrogen. All those techniques have to meet the provisional criterion of the Department of Energy of the United States (DOE). The DOE has established different targets for onboard hydrogen storage systems, including the minimum ‘‘gravimetric’’ and ‘‘volumetric’’ capacity and the reversibility of the charging/ discharging processes. For the year 2010, the storage system had to have a gravimetric capacity of 2 kWh kg–1 (6 wt. % of H2) and a volumetric capacity of 1.5 kWh L–1 (0.045 kg H2 L –1). In the case of the European Hydrogen & Fuel Cell Technology Platform, it requested energy density values of 1.1 kWh L–1 in its Strategic Research Agenda (SRA) and Deployment Strategy (DS) documents, published at the end of 2004, and reviewed in 2005.2 These energy density values are equivalent to a volumetric hydrogen storage capacity of about 33 g H2 L –1. It is important to note that, in the case of materials-based technologies, to achieve system-level capacities, the gravimetric and volumetric capacities of the material alone must clearly be higher than the system-level targets (depending on the material and the system design, material capacities may need to be higher by a factor of 1.2–2 times than system capacity targets3). These values are referred to the whole system, including the storage medium, the vessel, the refueling infrastructure, any regulators, electronic controllers, sensors, and so on. Recently, mesoporous carbons with well-ordered pore systems offered great potential in hydrogen storage.4–7 The carbons were obtained via the template method, which involved the introduction of suitable carbon precursors into the ordered pores of the template, followed by carbonization, and finally, removal of the template.8–10 These carbon materials usually have large specific surface areas and high pore volumes, which are useful for effective physisorption of H2. Besides, the ordered networks may provide fast transportation in the materials, a noticeable volume of micropores can efficiently adsorb hydrogen, and the microand the mesoporosity can be adjusted by changing the template, the carbon precursor, and the amount of carbon infiltrated in the template.11 In fact, hydrogen adsorption on carbon materials is strongly ascribed to surface heterogeneity, depending in its turn on their preparation and formulation. Surface heterogeneity can arise not only from surface irregularities, including bound impurities and functional groups, but also from nanopore polydispersity (structural heterogeneity). Highly-ordered Metal-modified Mesoporous Carbon Nitride: As a Novel Hydrogen Adsorbent