Recycling Carbon-based Wastewater Filters for Hydrogen Storage: a sustainable approach

Looking at the energy mix in recent years, it becomes clear that there is a need to make an energy transition towards renewable sources, especially in the transportation sector. Hydrogen, carrying high gravimetric energy density and being non-pollutant and regen-erative in nature, presents itself as the perfect candidate for substituting fossil fuels and addressing the fluctuations of natural energy sources, acting as an energy vector. Howev-er, the implementation of an energy system based on hydrogen (“Hydrogen Economy”) is impaired by some technical difficulties, regarding, most of all, its storage. As a matter of fact, hydrogen is characterized by an extremely low volumetric energy density, which requires the development of advanced techniques for its storage and transportation. Compared to traditional compressed and liquified hydrogen, storage in solid state mate-rials has shown to be more effective and safer, while also optimal for mobile applica-tions. Among all the materials studied for this application, activated carbons (ACs) have sparked a lot of interest due to their extremely high surface area and porosity, along with them being inexpensive and having good availability for industrial purposes. Additional-ly, they show higher adsorption reversibility when compared to other studied materials like metal hydrides. In particular, this research work focused on a particular type of AC, recycled from wastewater filters, which was studied to evaluate its performance in the storage of hydrogen. For this purpose, different parameters were investigated for the op-timization of this material. First, the influence of granulometry was investigated with samples ground at different particle sizes. A chemical activation with KOH was per-formed to increase the spent activated carbon’s specific surface area (SSA), and, lastly, a doping process was performed to introduce N heteroatoms using urea as a nitrogen pre-cursor. For all samples, extensive analysis of the textural parameters was performed by gas adsorption, while hydrogen uptake measurements were performed to evaluate the material’s performance in H2 storage.