Hydrogen storage potential of coals as a function of pressure, temperature, and rank

We conducted measurements of hydrogen adsorption on three coal samples of varying ranks at high pressure (0 to 102 bar) and elevated temperatures (303 K to 333 K) to assess their hydrogen storage potential. The excess adsorption capacity increased with increasing pressure but decreased with increasing temperature irrespective of coal rank. The highest hydrogen adsorption recorded was 0.721 mol/kg for the anthracite coal at 303 K and 102 bar. Furthermore, the hydrogen adsorption capacity correlated positively with coal vitrinite and fixed carbon contents (i.e. the high-rank coal exhibited greater adsorption), while all samples depicted predominantly type-I adsorption behavior for the entire pressure range. Micropore analysis and Fourier-transform infrared spectroscopy measurements were conducted to explore the microstructural and surface chemistry associated with these adsorption trends. The micropore content of the three samples followed the order: anthracite > sub-bituminous > bituminous, while H2 adsorption followed the trend: anthracite > bituminous > sub-bituminous - i.e., no direct correlation between coal micropore content and its H2 adsorption capacity - attributable to high clay content of bituminous coal which lowered its micropore content. Moreover, bituminous, and sub-bituminous samples exhibited an abundance of oxygen-containing functional groups, while anthracite coal depicted notable aromatic content - suggesting that the H-2 adsorption capacity is a complex function of coal surface chemistry and micropore content. Overall, high-rank coal seams at high pressure and temperature showed the largest hydrogen adsorption i.e., analogous to CO2 adsorption potential albeit at lower absolute values. These results, therefore, provide preliminary data on the hydrogen storage potential of coal seams and the associated scientific understanding of the mechanisms causing hydrogen adsorption. (c) 2022 Elsevier Inc. All rights reserved.

Automated summary

This study measured the hydrogen adsorption on coal samples of different ranks at high pressure and elevated temperatures to evaluate their hydrogen storage potential. The results showed that the excess adsorption capacity increased with pressure but decreased with temperature regardless of coal rank. The study also found a positive correlation between hydrogen adsorption capacity and coal vitrinite and fixed carbon contents. Micropore analysis and Fourier-transform infrared spectroscopy measurements were conducted to explore the microstructural and surface chemistry associated with the adsorption trends.