During ball milling, graphite can absorb a relatively large amount of hydrogen (7.4 wt %). However, during subsequent heating, hydrogen is usually desorbed together with a small amount of methane. Therefore, there is a need to understand the mechanism of hydrogen sorption. In this work, graphite samples were ball milled in a tungsten carbide pot under 3 bar hydrogen and then characterized by TGA-mass spectrometry, TEM, and Raman spectroscopy. It was found that the optimum milling time was 10 h, resulting in desorption of 5.5 wt % pure hydrogen (using a mass spectrometer) during heating under argon to 990 °C. In samples milled for longer than 10 h the amount of desorbed hydrogen decreased with methane being released in increasing amounts, while the amount of pure desorbed hydrogen was reduced for milling durations less than 10 h. The importance of milling time is discussed in terms of the different reaction steps between carbon and hydrogen atoms, leading to formation of methyl radicals, followed by evolution of methane.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Electronic, Optical and Magnetic Materials
- Surfaces, Coatings and Films
- General Energy