Mulch-assisted ambient-air synthesis of oxygen-rich activated carbon for hydrogen storage: A combined experimental and theoretical case study

Abstract

Most existing manufacturing protocols of functional carbon materials highly rely on inert media, which usually make them complicated and costly. In this work, an inert gas-free method for synthesizing oxygen-rich activated carbon has been developed. The inert gas-free synthesis is conducted simply by mixing the carbon precursor with chemical activator into a sand covered vessel followed by elevated temperature treatment under ambient atmosphere. Owing to the blocking effect of sand mulch and the overflow of self-generated pyrolysis volatiles, an in-situ pressure difference is built up to prevent air penetration, forming a local air-isolated atmosphere. Lignite-based activated carbon derived from the ambient-air process exhibits hierarchical pores with specific surface area of 823 m2/g. The hydrogen storage density of this ambient-air synthesized activated carbon is determined to be up to 0.34 wt% under 35 bar at 303 K, which is mainly attributed to the enriched oxygen-containing surface groups. DFT calculations suggest the adsorption enhancement of hydrogen follows the order of cis-COOH functionalized ≥ trans-COOH > OH functionalized activated carbon surfaces. This ambient-air strategy is potentially applicable all kind of precursors, and may open up a new avenue towards the low-cost synthesis of functional carbon materials.