| dc.description.abstract | While hydrogen is the most abundant chemical element in the universe, it cannot be considered a completely renewable energy source. However, due to its high energy density (40,000 Wh/kg) and its lack of harmful emissions to the environment, combining it with fuel cells can produce Fuel Cell Electric Vehicles (FCEVs), where the entire process only emits water or water vapor. Currently, the various stages of the hydrogen energy industry still have high costs. Developing low-cost graphitic carbon nitride (g-C3N4) nanotubes with rapid hydrogen adsorption and desorption kinetics, easy preparation, and large-scale production capabilities can initially reduce storage and operation costs, promoting the overall development of the hydrogen energy industry.
In this study, in order to investigate the preparation of g-C3N4 for mass production and its corresponding hydrogen storage performance, melamine powder and cyanuric acid powder with a weight ratio of 1 to 5 were mixed under different ball milling parameters to produce high-surface-area g-C3N4 nanotubes, providing more adsorption sites for hydrogen. In Method 3, ＂cataracting motion mode＂ at 110% (i.e. 150 rpm) of the critical speed exhibited the best grinding effect to provide the highest hydrogen content. The raw material particle size can be effectively reduced and and the partices can be uniformly mixed together, which would facilitate the subsequent chemical reactions during the calcination process. The effects of powder filling rates of 4.4%, 10%, 15%, and 20% in the milling jar were also discussed. It was found that when the filling rate exceeded 10%, insufficient grinding energy or ineffective ball milling space at lower speeds resulted in uneven mixing of melamine and cyanuric acid, leading to unreacted raw materials remaining after calcination. This resulted in a low proportion of nanotubes and an almost bulk-like substrate, limiting the increase in surface area. However, it was discovered that when pure g-C3N4 with high purity was produced, a ribbon-like lamellar intercalation structure was formed. Transmission electron microscopy (TEM) observation revealed the presence of potentially hollow nanotubes, which resulted in an increased surface area of 139.75 m2/g, much higher than that reported in many studies on g-C3N4 preparation.
Compared to high-density metal hydride hydrogen storage testing, low-density materials require more considerations for their hydrogen storage measurement ; otherwise, there may be issues of inaccuracy and low reproducibility due to measurement errors. In this work, special attention was given to volume calibration, temperature control, compressibility factor, and hydrogen content calculation in the hydrogen storage testing at room temperature. Pressure-Composition-Isotherm (PCI) tests were conducted using a Sieverts apparatus capable of high pressures up to 12 MPa, which is closer to the hydrogen storage capacity required for actual pressure target designated for the on board applications. With the measurement process remaining unaffected by environmental temperature fluctuations, the hydrogen storage capacity of g-C3N4 will exhibit an increase corresponding to the expansion of its surface area. In summary, applying a hydrogen charging pressure of 12 MPa would yield a hydrogen storage capacity range of 1.384 to 1.466 wt.% for g-C3N4. If large-scale production of ball-milled g-C3N4 is achievable, it would demonstrate both a high hydrogen storage capacity at room temperature and exceptional lightweight characteristics. This combination makes g-C3N4 nanotubes a promising candidate material for on board hydrogen storage. | en_US |