Calcium-atom-modified boron phosphide (BP) biphenylene as an efficient hydrogen storage material.

Porous nanosheets have attracted significant attention as viable options for energy storage materials because of their exceptionally large specific surface areas. A recent study (, 2024, , 33-39) has demonstrated that Li/Na-metalized inorganic BP-biphenylene (b-BP) and graphenylene (g-BP) analogues possess suitable functionalities for hydrogen (H) storage. Herein, we evaluate the H storage performance of alkaline earth metal (AEM = Be, Mg, Ca)-decorated b-BP and g-BP 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-BP and g-BP 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-BP (b-BP(Ca)) and g-BP (g-BP(Ca)) structures, forming stable and uniform Ca(Ca) ( and stand for the numbers of Ca atom) coverages on both sides. Under maximum hydrogenation, the b-BP(8Ca) and g-BP(16Ca) structures exhibited the ability to adsorb up to 32H and 48H molecules with average adsorption energy ( ) values of -0.23 eV per H and -0.25 eV per H, respectively. Gravimetric H uptakes of 7.28 wt% and 5.56 wt% were found for b-BP(8Ca)@32H and g-BP(16Ca)@48H 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-BP and g-BP sheets for H storage technologies.