Controls of Geological Factors on H₂ Adsorption in the Subsurface

Area of Science:

• Geochemistry
• Subsurface Energy Storage

Background:

• Underground hydrogen storage is crucial for a stable hydrogen economy.
• Understanding geological factors affecting hydrogen (H2) recovery and sorption is vital for safe and efficient storage.

Purpose of the Study:

• To investigate the impact of geological factors on H2 sorption in organic-rich and lean rock samples.
• To compare H2 and methane (CH4) adsorption in coals and smectite under varying conditions.

Main Methods:

• Adsorption measurements of H2 and CH4 on coals and smectite at temperatures of 35–65 °C and pressures up to 15 MPa.
• Langmuir monolayer modeling to analyze adsorption data.
• Comparison of sorption behavior between different rock types.

Main Results:

• Coal samples exhibited significantly higher H2 and CH4 adsorption than smectite.
• BET surface area is important for H2 sorption, but chemical structure, particularly organic oxygen-containing functional groups, plays a critical role.
• Coal seams can store at least 30% more H2 compared to the free phase under similar geological conditions, primarily through physical sorption.

Conclusions:

• Geological factors, including surface area and chemical composition, control H2 sorption in subsurface formations.
• Hydrogen storage in coal seams is a promising option, with enhanced capacity due to physical sorption mechanisms.
• Further understanding of these interactions is essential for optimizing geological hydrogen storage.