القسم: قسم العلوم الطبيعية
الجهة البحثية: الجامعة اللبنانية الامريكية
عنوان البحث المنش ور: Boron-neutron Capture on Activated Carbon for Hydrogen Storage
سنة النشر: 2019
ملخص البحث المنشور:
Hydrogen is currently stored and transported either in compressed or liquefied forms. However, an alternative method for hydrogen storage using chemisorption or physisorption in host materials has emerged as a practical and safe technology for various applications. In host materials like metal and chemical hydrides, hydrogen forms bonds with the host through covalent, ionic, or metallic-type bonds. Chemisorption, where the bonding is hardly reversible, necessitates high temperatures or exposure to a catalyst for hydrogen release. In contrast, physisorption occurs as hydrogen molecules are weakly attracted to the sorbent surface through van der Waals forces, resulting in a high-density fluid adsorption. While physisorption has relatively low heat of adsorption and, thus, low storage capacities, numerous research efforts have been dedicated to developing an efficient hydrogen sorbent. Metal-organic frameworks and activated carbons are the most promising materials for hydrogen storage via physisorption. Many attempts have been made to enhance the surface chemistry and pore size distribution of existing activated carbons. These efforts involved altering the pore structure through optimization of the activation process and modifying surface chemistry by introducing elements such as boron, aluminum, lithium, and calcium. Despite these attempts resulting in marginal improvements, they have aligned with the theoretical limit of the existing activated carbon structure for hydrogen storage. This research presents a novel method of modifying activated carbon structure using high-energy fission tracks. Boron-doped activated carbons were irradiated by neutrons to induce defects and alter the pore surface and structure. With an isotopic abundance of around 20%, 10B binds strongly with thermal neutrons to form an excited 11B nucleus. This unstable nucleus decays through fission, producing a lithium nucleus, helium nucleus, and gamma photon, thereby altering the surface and structure of the pores in activated carbon. Modeling the defects introduced by fission tracks assumes a slit-shaped pore geometry. Sub-critical nitrogen adsorption indicates that nitrogen molecules cannot explore the defects created by fission tracks. However, hydrogen adsorption isotherms of irradiated samples reveal higher binding energies compared to their non-irradiated counterparts. Consequently, neutron irradiation of boron-doped activated carbons changes the surface and pore structure, introducing defects that act as high-energy binding sites for adsorbed hydrogen. This leads to a 6% increase in average binding energies in irradiated samples compared to non-irradiated ones. Furthermore, this increase is more significant at low coverage, resulting in a 9% increase in hydrogen storage capacities in the low-pressure range (P < 42 bar).
رابط البحث المنشور:
https://www.nature.com/articles/s41598-019-39417-6