With the exhaustion of traditional fossil fuel resources and the implementation of global sustainable development strategy, the development and application of new alternative energy materials has become a general trend. Hydrogen energy is known as the green energy of the 21st century. When it comes to hydrogen application, hydrogen storage is a key link so the development of hydrogen storage materials has been widely concerned by researchers. As a new kind of important gas storage material, carbon material has become a hot spot in the development and research of hydrogen storage materials.
- Super activated carbon Activated carbon hydrogen storage is an adsorptive hydrogen storage technology using super activated carbon with high specific surface area as adsorbent at low temperature and medium pressure. Activated carbon is featured by large adsorption capacity, good chemical stability, easy desorption and others. There are many pores with different sizes and shapes in the structure of activated carbon including micropores, mesopores and macropores. Macropores are mainly used to control the adsorption speed. Mesopore, like macropore, also controls the adsorption velocity. Moreover, it also acts as an adsorption point for larger molecules that cannot enter the micropore. Micropores are composed of fine capillary walls, which can increase the surface area of materials and increase the adsorption capacity correspondingly. Compared with other hydrogen storage technologies, super activated carbon hydrogen storage has the advantages of economy, high hydrogen storage capacity, fast desorption, long cycle life and easy to achieve large-scale production, which is a promising method for hydrogen storage.
Figure 1. Schematic structure of a super activated carbon.
- Nanostructured carbon: Nanostructured carbon used as hydrogen storage materials mainly include graphite nanofiber, carbon nanofiber and carbon nanotube. The graphite nanofiber contains many very small graphite sheets, the width of the sheets is about 3-50 nm. The sheets are stacked together regularly with a spacing of 0.34 nm. Moreover, carbon nanofibers are carbon fibers with solid structure and the fiber diameter is less than 1000nm. A research team opened carbon nanofibers and removed impurities and oxygen-containing functional groups on the fiber surface. The maximum hydrogen storage capacity of carbon nanofibers was determined to be 10 percent of the mass fraction. In addition, since carbon nanotubes were discovered by Japanese scientists in 1991, they have rapidly become a hot research topic in hydrogen storage field because of their unique one-dimensional tubular molecular structure and special mechanical and electrical properties. Compared with active carbon, carbon nanotubes have a larger specific surface area and more number of micropores. Their hydrogen storage capacity is likely to be much higher than that of conventional hydrogen storage materials. Therefore, carbon nanotubes are considered as a promising hydrogen storage material.
Figure 2. An example of nanostructured carbon hydrogen storage material.
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- Adeniran B, Mokaya R. Low temperature synthesized carbon nanotube superstructures with superior CO2 and hydrogen storage capacity[J]. Journal of Materials Chemistry A, 2015, 3(9):5148-5161.