(383aw) Sustainable and Cost-Effective Silica-Based Materials for Hydrogen Storage

The rapid transition to renewable energy sources is the key breakthrough in limiting CO₂ emissions and realizing carbon neutrality goals (1). Solid-state H₂ storage in physisorption materials, which is characterized by a low heat of adsorption of 4-10 kJ/mol H₂ (2), rapid adsorption/desorption kinetics, and full reversibility is one of the promising approaches. However, most of these materials suffer from low adsorption capacities under mild conditions to different degrees. Moreover, carbon nanotubes and graphene derivatives are expensive and have complex synthesis procedures, and MOFs have stability and processability issues and generally involve expensive fabrication processes. COFs also have stability problems and difficulty in activation, although they are a relatively new class of materials with high surface area and crystallinity (3). Therefore, among this variety of solid-state H₂ storage materials, owing to their environmental compatibility, relatively easy preparation method, and low cost, significant attention must be devoted to materials based on activated carbon and mesoporous silica.

In this study, sustainable rice husk ash-derived MCM-41-RHA and SBA-15-RHA mesoporous silica materials were developed. These materials were engineered with different levels of Ni loading (2.5-10 wt%) and are used for H₂ storage. The prepared MCM-41-RHA and SBA-15-RHA materials have a high BET-specific surface area of 1,092.6 m²/g and 539.2 m²/g, respectively, with a mesopore distribution. The best results were observed for samples with a Ni loading of 5 wt%, such as MCM-41-RHA-Ni5 and SBA-15-RHA-Ni5, which demonstrated the highest H₂ uptake of 3.64 wt% and 2.48 wt%, respectively, at 77 K and 1 bar (Figure 1). This was due to the strong interaction between the adsorbent and split over hydrogen despite the decrease in the BET-specific surface area after the incorporation of Ni. The enhanced interaction was evidenced by the increased isosteric heat of adsorption observed for MCM-41-RHA-Ni5 and SBA-15-RHA-Ni5, ranging from 21.1 to 8.1 kJ/mol, in contrast to the range of 6.9 to 4.1 kJ/mol for the pristine MCM-41-RHA and SBA-15-RHA. After five successive H₂ uptake/release cycles, more than 92 % of the initial capacity was retained. This study presents a sustainable and cost-effective RHA-derived mesoporous silica material decorated with Ni- nanoparticles for solid-state H₂ storage.