Hydrogen Underground Storage in Silica-Clay Shales: Experimental and Density Functional Theory Investigation

In the context of reducing the global emissions of greenhouse gases, hydrogen (H₂) has become an attractive alternative to substitute the current fossil fuels. However, its properties, seasonal fluctuations, and the lack of extended energy stability made it extremely difficult to be economically and safely stored for a long term in recent years. Therefore, this paper investigated the potential of shale gas reservoirs (rich and low clay-rich silica minerals) to store hydrogen upon demand. Density functional theory molecular simulation was employed to explore hydrogen adsorption on the silica-kaolinite interface, and the physisorption of hydrogen on the shale surface is revealed. This is supported by low adsorption energies on different adsorption configurations (0.01 to -0.21 eV), and the lack of charge transfer showed by Bader charge analysis. Moreover, the experimental investigation was employed to consider the temperature (50-100 °C) and pressure (up to 20 bar) impact on hydrogen uptake on Midra shale, specifically palygorskite (100%), which is rich in silicate clay minerals (58.83% SiO₂). The results showed that these formations do not chemically or physically maintain hydrogen; hence, hydrogen can be reversibly stored. The results highlight the potential of shale gas reservoirs to store hydrogen as no hydrogen is adsorbed on the shale surface, so there will be no hydrogen loss and no adverse effect on the shale's structural integrity, and it can be safely stored in shale reservoirs and recovered upon demand.