Revealing contribution of pore size to high hydrogen storage capacity

Abstract

Understanding the influence of pore structure on hydrogen storage behaviour is fundamental to develop high-performance hydrogen adsorbents. Nevertheless, there are rare compellent evidences to clearly clarify the relationship between pore size and hydrogen storage performance in porous materials. The main reason could be ascribed to the lack of appropriate porous model structures. Herein, we propose an interesting and convincing insight into the aforementioned important issue by designing proper well-defined three types of porous carbon materials with different pore size distributions. Except for the pore size distribution, these porous carbons are derived from the same source (i.e., chitosan), and have very similar surface area of ca. 3300 m2 g−1, grain morphology and carbon microcrystalline framework structure. With these features, the obtained carbon materials can be adopted as appropriate objects to evaluate the correlation of the pore size with the hydrogen storage performance. It is demonstrated that the presence of nanopore with size from 1.5 to 2.5 nm can significantly improve high-pressure hydrogen storage capacity. Moreover, nanopores with size below 1.5 nm are indeed the most efficient hydrogen storage spaces no matter at low pressures or high pressures, whereas those mesopores with size above 2.5 nm are believed to not participate in the hydrogen storage. These results convincingly indicate that there indeed exists a strong contribution of the pore size to high hydrogen storage capacity.