Hydrogen diffusion in coal: Implications for hydrogen geo‐storage

Hypothesis Hydrogen geo-storage is considered as an option for large scale hydrogen storage in a full-scale hydrogen economy. Among different types of subsurface formations, coal seams look to be one of the best suitable options as coal’s micro/nano pore structure can adsorb a huge amount of gas (e.g. hydrogen) which can be withdrawn again once needed. However, literature lacks fundamental data regarding H2 diffusion in coal. Experiments In this study, we measured H2 adsorption rate in an Australian anthracite coal sample at isothermal conditions for four different temperatures (20°C, 30°C, 45°C and 60°C), at equilibrium pressure ∼13 bar, and calculated H2 diffusion coefficient ( D H 2 ) at each temperature. CO2 adsorption rates were measured for the same sample at similar temperatures and equilibrium pressure for comparison. Findings Results show that H2 adsorption rate, and consequently D H 2 , increases by temperature. D H 2 values are one order of magnitude larger than the equivalent D C O 2 values for the whole studied temperature range 20-60 °C. D H 2 / D C O 2 also shows an increasing trend versus temperature. CO2 adsorption capacity at equilibrium pressure is about 5 times higher than that of H2 in all studied temperatures. Both H2 and CO2 adsorption capacities, at equilibrium pressure, slightly decrease as temperature rises.