Hexagonal boron nitride (h-BN) is a two-dimensional (2D) layered material with a structure similar to graphite and it has potential as a hydrogen and ammonia storage material. However, dense packing in the standard h-BN structure limits its surface area and prevents the B and N from being adsorption sites. In this study, the addition of Mg²⁺ during h-BN synthesis facilitated the growth of lattice dislocations and led to a cross-linked three-dimensional (3D) porous structure. A proposed formation mechanism for porous h-BN was confirmed by several characterization routes, most clearly by high-resolution transmission electron microscopy (HRTEM). Porous Mg/BNs exhibited high H₂ and NH₃ uptakes and showed potential for H₂ and NH₃ storage.