| 摘要: | 雖然氫是宇宙中最豐富的化學元素，但它不能被視為完全可再生的能源。然而，由於其能量密度高（40,000 Wh/kg）且不會對環境產生有害排放，將其與燃料電池結合可以生產燃料電池電動汽車（FCEV），整個過程僅排放水或水蒸氣。目前，氫能產業各階段成本仍然較高。開發具有快速吸氫和解吸動力學、易於製備和規模化生產能力的低成本石墨相氮化碳（g-C3N4）奈米管，可以初步降低儲存和運行成本，促進氫能產業的整體發展。
本研究為了研究可量產g-C3N4的製備及其相應的儲氫性能，將三聚氰胺粉末和氰尿酸粉末以1比5的重量比在不同的球磨參數下混合，生產出高比表面積的g-C3N4奈米管，為氫提供更多的吸附位點。在方法3中，“cataracting運動模式”在臨界轉速的110%（即150rpm）時表現出最好的研磨效果，以提供最高的氫含量。可以有效降低原料粒徑，使顆粒均勻混合，有利於後續煅燒過程中的化學反應。還討論了研磨罐中粉末填充率 4.4%、10%、15% 和 20% 的影響。研究發現，當填充率超過10%時的低轉速下，研磨能量不足或球磨空間不足導致三聚氰胺和三聚氰酸混合不均勻，導致煅燒後殘留未反應的原料。這導致奈米管比例較低，基底幾乎呈塊狀，限制了表面積的增加。然而，發現當生產高純度的純g-C3N4時，會形成帶狀層狀插層結構。透射電子顯微鏡 (TEM) 觀察揭示了潛在中空奈米管的存在，這導致表面積增加到 139.75 m2/g，遠高於許多 g-C3N4 製備研究中報導的值。
與高密度金屬氫化物儲氫測試相比，低密度材料的儲氫測量需要更多考慮；否則，可能會因測量誤差而出現不准確和再現性低的問題。在這項工作中，特別關注了室溫儲氫測試中的體積校準、溫度控制、壓縮因子和氫含量計算。壓力成分等溫線 (PCI) 測試使用能夠承受高達 12 MPa 高壓的 Sieverts 裝置進行，該裝置更接近為車載應用指定的實際壓力目標所需的儲氫能力。在測量過程不受環境溫度波動影響的情況下，g-C3N4的儲氫能力將隨著其表面積的擴大而增加。總之，施加12 MPa的充氫壓力將使g-C3N4的儲氫容量範圍為1.384至1.466 wt.%。如果球磨g-C3N4的大規模生產能夠實現，它將表現出室溫下的高儲氫能力和卓越的輕質特性。這種組合使得 g-C3N4 奈米管成為一種有前途的車載儲氫候選材料。
;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. |
