Porous nanosheets have attracted significant attention as viable options for energy storage materials because of their exceptionally large specific surface areas. A recent study (Int. J. Hydrogen Energy, 2024, 66, 33-39) has demonstrated that Li/Na-metalized inorganic BP-biphenylene (b-B3P3) and graphenylene (g-B6P6) analogues possess suitable functionalities for hydrogen (H2) storage. Herein, we evaluate the H2 storage performance of alkaline earth metal (AEM = Be, Mg, Ca)-decorated b-B3P3 and g-B6P6 structures based on first-principles density functional theory (DFT) calculations. Our investigations revealed that individual Be and Mg atoms are not stable on pure b-B3P3 and g-B6P6 sheets, and the formation of aggregates is favored due to their low binding energy to these surfaces. However, the binding energy improves for Ca-decorated b-B3P3 (b-B3P3(mCa)) and g-B6P6 (g-B6P6(nCa)) structures, forming stable and uniform mCa(nCa) (m and n stand for the numbers of Ca atom) coverages on both sides. Under maximum hydrogenation, the b-B3P3(8Ca) and g-B6P6(16Ca) structures exhibited the ability to adsorb up to 32H2 and 48H2 molecules with average adsorption energy (E a) values of -0.23 eV per H2 and -0.25 eV per H2, respectively. Gravimetric H2 uptakes of 7.28 wt% and 5.56 wt% were found for b-B3P3(8Ca)@32H2 and g-B6P6(16Ca)@48H2 systems, exceeding the target of 5.50 wt% set by the US Department of Energy (DOE) to be reached by 2025. Our findings indicate the importance of these b-B3P3 and g-B6P6 sheets for H2 storage technologies.
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